Amplitude regulating circuit

An amplitude regulating circuit for an oscillator with an input for a supply signal having an electrical quantity depending on an amplitude of an oscillation of the oscillator has a supply circuit with a control input for a first control signal and a supply output for the supply signal based on the first control signal, a reference circuit with an input for a reference supply signal having a reference quantity, a reference supply circuit with a reference control input for a second control signal and a reference supply output for the reference supply signal based on the second control signal and a comparator circuit with a first control signal output for the first control signal based on the electrical quantity and the electrical reference quantity and a second control signal output for the second control signal based on the electrical quantity and the electrical reference quantity.

This application claims priority from German Patent Application No. 10 2006 032 276.2, which was filed on Jul. 12, 2006, and is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an amplitude regulating circuit, in particular an amplitude regulating circuit for an oscillator, which may, for example, be a voltage-controlled oscillator (VCO).

BACKGROUND

Nowadays, radio frequency switching circuits or RF switching circuits are implemented in many electronic apparatuses and utilized, for example, as clock generators or basic frequency generators for receiving and/or transmitting units for data transfer by radio. Respective radio frequency switching circuits are employed both in mobile apparatuses and in apparatuses, which tend to be used in the non-mobile field. Examples of respective mobile apparatuses are portable minicomputers such as PDAs (PDA=personal data assistant) or cell phones.

Frequently, fully integrated phase-locked circuits or PLL circuits (PLL=phase-locked loop) are realized in the respective RF switching circuits. Often, the core of such a phase-locked circuit is a voltage-controlled oscillator or VCO, which is dimensioned such that it tolerates scatterings regarding the frequency, which may occur, for example, as a result of productional and/or operational parameters (temperature variations or variations in the supply voltage), and still constantly generates the desired frequency. Next to balancing the scattering due to production, temperature and supply voltage, the VCO or the corresponding RF switching circuit must also often cope with various frequency bands, which is why an integrated VCO must generally be controllable across a large frequency range. Therefore, the VCO tolerates these scatterings and is capable of balancing the (current) frequency such, with the aid of adjustable components (tuning components), that in the end it will generate the correct frequency.

With voltage-controlled oscillators covering a large frequency and temperature range, it is therefore advisable to pay particular attention to an amplitude of an oscillation provided by the voltage-controlled oscillator (output amplitude) as same basically largely depends on the respective operating conditions. In order to ensure safe functioning of the overall circuit it is therefore generally necessary that the output amplitude or amplitude be large enough to be able to drive subsequent circuits. At the same time, in a corresponding design of the respective RF switching circuit, it must be taken into consideration that often only a limited amount of energy is available for the operation of the respective IC (IC=integrated circuit). This particularly applies to mobile applications, in which battery-powered or accumulator-powered ICs are often employed. In order to maximize the battery or accumulator lifetime, it is therefore advisable to provide a minimum amount of current for the operation of the respective RF switching circuit, which may lead to significant limitation of the specified parameters of the RF switching circuit.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, an amplitude regulating circuit for an oscillator with an input for a supply signal having an electrical quantity depending on an amplitude of an oscillation of the oscillator comprises a supply circuit with a control input for a first control signal and a supply output for the supply signal based on the first control signal, a reference circuit with an input for a reference supply signal having a reference quantity, a reference supply circuit with a reference control input for a second control signal and a reference supply output for the reference supply signal based on the second control signal, and a comparator circuit with a first input coupled to the supply output, a second input coupled to the reference supply output, a first control signal output for the first control signal based on the electrical quantity and the electrical reference quantity coupled to the control input, and a second control signal output for the second control signal based on the electrical quantity and the electrical reference quantity coupled to the reference control signal input.

According to an embodiment of the present invention, an amplitude regulating circuit for a voltage-controlled oscillator with an input for a supply current having a voltage value depending on an amplitude of an oscillation of the voltage-controlled oscillator, comprises a supply circuit with a control input for a first control signal and a supply output for the supply current based on the first control signal, a reference circuit with an input for a reference supply current and a resistive element coupled to the input of the reference circuit, a reference supply circuit with a reference control input for a second control signal and a reference supply output for the reference supply current based on the second control signal and a comparator circuit with a comparator circuit and a voltage source, one output of the comparator circuit being coupled to the control input of the supply circuit and/or the reference control input of the reference control circuit, the input of the oscillator being connected to a non-inverting input of the comparator circuit320, and the input of the reference circuit being coupled to a first terminal of the voltage source and a second terminal of the voltage source being coupled to an inverting input of the comparator circuit.

According to an embodiment of the present invention, an amplitude regulating circuit for an oscillator with an input for a supply signal having an electrical quantity depending on an amplitude of an oscillation of the oscillator comprises supply means for providing the supply signal based on a control signal, reference means for a reference supply signal having an electrical reference quantity, reference supply means for providing the reference signal based on the control signal, and comparison means for comparing the electrical quantity to the electrical reference quantity and for providing the control signal based on the comparison of the electrical quantity with the electrical reference quantity.

According to an embodiment of the present invention, a method for regulating an amplitude of an oscillation of an oscillator with an input for a supply signal having an electrical quantity depending on an amplitude of the oscillation of the oscillator and with a reference circuit with an input for a reference supply signal having an electrical reference quantity comprises a step of comparing the electrical quantity with the electrical reference quantity in order to obtain a comparison result, and a step for providing the supply signal and the reference supply signal based on the comparison result.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Before in the further course of the present application further embodiments of the present invention in the form of amplitude regulating circuits are discussed with respect toFIGS. 4-6b, first, a first embodiment of an amplitude regulating circuit is discussed with respect toFIG. 1, and a structure of a typical voltage-controlled oscillator is discussed in greater detail with respect toFIGS. 2,3a, and3b.

FIG. 1shows a block diagram of a first embodiment of the present invention in the form of an amplitude regulating circuit100for an oscillator110with an input for a supply signal. The oscillator110may, for example, be a voltage-controlled oscillator (VCO) or another type of oscillator, which can be controlled or regulated at least with respect to one amplitude of a frequency signal output thereby. A supply output of a supply circuit120is connected to the input for the supply signal of the oscillator110. In addition to the supply output, the supply circuit120also comprises a control input coupled to a first control signal output of a comparator circuit130. In addition, a first input for the supply signal of the comparator circuit130is coupled to an input of the oscillator and the supply output of the supply circuit120.

Moreover, the comparator circuit130is coupled to a reference supply circuit140via a second control signal output and a second input. More precisely, a reference control input of the reference supply circuit140is coupled to the second control signal output of the comparator circuit130. In addition, the reference supply circuit140moreover comprises a reference supply output coupled to the second input of the comparator circuit130. Moreover, an input of a reference circuit150is coupled to the reference supply output of the reference supply circuit140.

In the context of the present invention, a coupling of two components means a direct or indirect connection of the respective components, for example, via one or more further electrical switching elements.

The supply circuit120provides to the oscillator110a supply signal having an electrical quantity, i.e., for example, a current value or a voltage value depending on an amplitude of an oscillation of the oscillator110. The supply signal is also provided to the comparator circuit130via the first input thereof.

In a quasi mirror-inverted manner with respect to the supply circuit120and the oscillator110, the reference supply circuit140provides to the reference circuit150a reference supply signal, which is also provided to the comparator circuit130via the second input.

Here, the reference supply signal also comprises an electrical reference quantity, which again may be a current value or a voltage value. On the basis of the electrical quantity of the supply signal and the electrical reference quantity of the reference supply signal, the comparator circuit130now generates a first control signal and a second control signal, which are provided to the two supply circuits, more precisely, to the supply circuit120and the reference supply circuit140, via their control signal input and reference control signal input respectively.

Via the supply signal, the supply circuit120provides an energy necessitated for the oscillation to the oscillator110. If, for example, a certain amount of energy is drawn off the oscillator110in each oscillation or during each period of an oscillation via an output not shown inFIG. 1for a frequency signal generated by the oscillator110comprising the respective oscillation, and by a circuit also not shown inFIG. 1, same can be re-supplied to the oscillator110via the supply signal of the supply circuit120. Moreover, energy losses resulting from internal losses of the oscillator110may also be compensated for via the supply signal.

The oscillator110is configured such or comprises the feature that the electrical quantity of the supply signal, i.e., for example, a voltage value or a current value of the supply signal, is dependent on the amplitude of the oscillation of the oscillator110. If the supply signal provided to the oscillator110is, for example, a current, the oscillator110may be configured or designed such that a voltage value at its input depends on the amplitude of the oscillation. In this case, the voltage value of the current acting as the supply signal is the electrical quantity of the supply signal. Analogously, in the case of an oscillator110to which a voltage is provided, i.e. in which the supply signal represents an electrical voltage, a current value may indicate the amplitude of the oscillation of the oscillator110.

The reference circuit150and the reference supply circuit140are commonly configured such that same enable a regulation of the supply circuit120and the oscillator110via the comparator circuit130, without the oscillator110being loaded at its output not shown inFIG. 1. In other words, the reference supply circuit140and the reference circuit150are adapted to the oscillator110and the supply circuit120with respect to a characteristic quantity such as a voltage curve or current curve. Still in other words, a stable reference quantity is generated by means of the reference circuit150, by which the amplitude of the oscillation, for example, the VCO amplitude, is determined with no load applied.

The comparator circuit130drives the two supply circuits120,140based on the supply signal and the reference supply signal such that a (quasi) constant oscillation amplitude of the oscillator110across a large temperature range is achieved. If, moreover, the oscillator110is an oscillator with a variable frequency, for example, a voltage-controlled oscillator or VCO, the embodiment of an amplitude regulating circuit shown inFIG. 1may guarantee a (quasi) constant oscillation amplitude of the VCO110as a whole across a large frequency and temperature range.

One advantage of an embodiment of the present invention is the fact that the amplitude of the oscillator110may be controlled and regulated without having to load the output of the oscillator110by a measurement of the amplitude. Therefore, the embodiment of the present invention enables a regulation of the amplitude of the oscillator110, wherein no load must be placed on the output of the oscillator110. This makes it possible to operate the oscillator110in a particularly energy-saving mode of operation, as a change of the amplitude of the oscillation provided by the oscillator in the form of a frequency signal may be compensated for by operational parameters such as the frequency of the oscillator110or by environmental influences such as the temperature or the supply voltage.

This makes it possible to configure the oscillator110such that the amplitude of the oscillation may be optimally adjusted to the requirements of the subsequent switching elements. It is therefore no longer necessary to operate the oscillator110, among all (specified) operating conditions, in a mode of operation guaranteeing a lower limiting value of the amplitude of the oscillation, which in general results in an excessive amplitude of the oscillation compared to the lower limiting value and, therefore, in excessive energy consumption of the oscillator110.

This is achieved by connecting a reference circuit150“in parallel” or “in a mirror-inverted manner” to the oscillator110on the supply side, the reference circuit150, together with the reference supply circuit140, being adapted thereto with respect to a characteristic quantity of the oscillator110and the supply circuit120so that the reference circuit150provides a stable reference quantity, based on which the comparator circuit130may provide the two supply circuits120,140with control signals.

In an embodiment of the present invention, the reference circuit thus comprises, for example, a resistive element coupled to the input of the reference circuit150and the reference supply signal is applied. Moreover, in a further embodiment of the present invention, the reference circuit150may also comprise a reference transistor being adapted to one or more transistors comprised in the oscillator110with regard to its dimensioning and configuration. Hereby, the reference circuit150is able to simulate, for example, a temperature dependence or other environmental influences of the oscillator110, which represents a significant advantage of the respective embodiments.

A further advantage of an embodiment of the present invention is the fact that the reference circuit150and the reference supply circuit140are configured such with respect to the supply circuit120and the oscillator110that the reference supply signal and the supply signal have a predetermined ratio to each other. Thereby, the amplitude of the oscillation may be regulated very precisely if, as in the typical case, the ratio of a value of the supply signal to the value of the reference supply signal is in a range between 0.75 and 1.25 or else in a range between 0.9 and 1.1.

In the further course of the present invention the same reference numerals are used for objects, which are equal or similar in function. Sections of the description referring to objects equal or similar in function may be interchanged among the individual embodiments unless explicitly claimed otherwise.

Before further embodiments of the present invention in the form of amplitude regulating circuits are discussed in the further course of the present application, first a voltage-controlled oscillator, oscillator110, will be discussed with respect to the equivalent circuit diagram shown inFIG. 2and the curves of an amplitude of an oscillation of the voltage-controlled oscillator illustrated inFIGS. 3aand3b.

Thus,FIG. 2shows an equivalent circuit diagram of a conventional realization of a voltage-controlled oscillator110, which may be utilized, for example, as the oscillator110in the embodiment shown inFIG. 1. Like the oscillator110in the embodiment shown inFIG. 1, the voltage-controlled oscillator or VCO110comprises an input for a supply signal, to which inFIG. 2a current source160is connected impressing upon the VCO110a direct current with a current value IVCO. In addition, the current source160is connected to a supply terminal170for a positive supply voltage Vdd.

The VCO110comprises a parallel oscillator circuit, which may be connected via two cross-coupled transistors180,190to a terminal for a reference potential200, which may, for example, be ground (GND) or a negative supply voltage Vss. More precisely, the (parallel) oscillator circuit comprises a coil or inductivity210comprising a mid-connection or mid tap the input of the oscillator110is coupled to. The inductivity210has an inductivity value L. The inductivity210may exist in the form of a coil or an oscillator circuit coil, a correspondingly shaped conductive trace on a chip or, for example, a semiconductor circuit such as a gyrator. Depending on the actual design of the inductivity210, the same may also comprise a series connection of two of the above-mentioned switching elements or circuits, wherein between the two switching elements the mid tap or central tap may be implemented in the form of a node. In addition, the inductivity210serves to decouple the oscillation from the (direct) current source160as the inductivity here also represents a low-pass filter for the current source160.

A capacity220, which may be adjusted or trimmed with respect to its capacity value, is connected in parallel to the inductivity210. In the VCO110shown inFIG. 2, the capacity220has a capacity value Ctune, which may be adjusted by applying a control voltage Vtuneto a control terminal of the capacity220. A respective adjustable capacity220, which is also referred to as Ctune trim capacity, may be realized, for example, by means of varactors or capacity diodes. A respective trim capacity may, for example, be embodied in the form of a series connection of two capacity diodes, the cathode terminals of the two capacity diodes each being connected via a node, and the node being coupled to the control terminal of the trim capacity. It may be advisable to integrate additional isolation capacitances and/or capacities connected in parallel into the trim capacity.

Moreover, in the VCO110shown inFIG. 2, one drain terminal of one of the two transistors180,190each, which are (normally off) n-channel field-effect transistors and/or (enhancement) NMOS transistors, are shown. In addition, the two transistors180,190are each connected to a reference potential terminal200via their source terminals. The gate terminals of the two transistors180,190are connected crosswise to the respective drain terminals of the respective other transistor180,190. More precisely, the gate terminal of the transistor180is connected to the drain terminal of the transistor190, and the gate terminal of the transistor190is connected to the drain terminal of the transistor180. Here, the two field-effect transistors180,190have ratios of the widths W of the channels of the two transistors to a length LKof the two channels, which are identical for both transistors180,190within the production tolerances.

It should be noted here that the two NMOS transistors180,190may also be replaced by npn bipolar transistors. In this case, the two NMOS transistors180,190must be substituted by the two npn bipolar transistors such that the two drain terminals must be replaced by the collector terminals, the source terminals must be replaced by the emitter terminals, and the gate terminals of the NMOS transistors must be replaced by the base terminals of the npn bipolar transistors. On this basis of the n-channel field-effect transistors and the npn bipolar transistors being symmetrical, in the further course of the present application, a source terminal may be a source terminal or an emitter terminal, a drain terminal may be a drain terminal or a collector terminal, and a gate terminal may be a gate terminal or a base terminal or the respective transistor, depending on the type of transistor used.

The oscillator circuit of the VCO110shown inFIG. 2in addition comprises a loss resistor230, which is represented inFIG. 2by its conductance G and into which, for the sake of simplification all circuit losses of the VCO110occurring, are integrated. Moreover, the oscillator circuit of the VCO110comprises two output terminals240-1,240-2, which are connected to a terminal of each inductivity210, loss resistor230, and capacity220. During the operation of the VCO110, a (partial) frequency signal in the form of a voltage with the voltage value u(t), may be tapped at each of the two output terminals240-1,240-2. Herein, the frequency signal with the voltage values:
u(t)=Û·sin(2π·f·t)  (1)

may be tapped at the output terminal240-1, Û being the amplitude of the oscillation, f being the frequency, t being the time, and π being the Ludolph's constant. Accordingly, a frequency signal with the voltage values:
u(t)=Û·sin(2π·f·t)  (2)

may be tapped for reprocessing at the second output terminal240-2. The VCO110illustrated inFIG. 2in addition enables doubling the amplitude of the frequency signal as compared to the use of only a single output terminal240-1,240-2by using both output terminals240-1,240-2as the output of the VCO110in a differential manner, wherein direct current portions, which may occur at the two output terminals240-1,240-2, are eliminated simultaneously.

Here, the frequency signal of the oscillator or VCO110has an oscillating frequency f, which is inversely proportional to the root of the product of the inductivity value L of the inductivity210and the capacity value C=Ctune of the adjustable capacity220. Therefore,

As for many adjustable capacities220their capacity values C are inversely proportional to the square of the control voltage Vtunepresent at the gate terminal, i.e., as:
C˜1/vtune2(4),

the oscillating frequency or natural frequency of the VCO110results in being substantially proportional to the control voltage Vtunein the case of an ideally controlled capacity, so that:
f˜Vtune(5).

Moreover, the oscillator circuit of the VCO110has a quality value Q or an oscillator circuit quality Q, which is essentially proportional to the root of the quotient of the inductivity value L of the inductivity210and the capacity value C of the capacity220, so that:

Moreover, the oscillation amplitude Û is essentially proportional to the square of the oscillator circuit quality Q and the current IVCOprovided to the VCO110by the current source160, so that furthermore:
Û˜IVCO, Q2(7).

Together with the equations (4) and (5), the oscillation amplitude or the amplitude of the oscillation Û results in being dependent on the control voltage Vtuneof the capacity220. More precisely, the amplitude of the oscillation Û is proportional to the square of the control voltage Vtuneso that:
Û˜Vtune2(8).

If the VCO110is operated in a small environment of a predetermined operating point with respect to the control voltage Vtune, both the dependence of the oscillator circuit frequency or natural frequency of the VCO110and the amplitude of the oscillation Û may be approximated by a linear approximation. In the case of relatively small frequency changes, caused by a change of the control voltage Vtune, the following approximations with respect to the natural frequency or oscillator circuit frequency or frequency f of the oscillation and with respect to the oscillation amplitude or amplitude of the oscillation Û are yielded:
f˜Vtune(9)
Û˜Vtune(10)

If an operating current IVCOis fed to the oscillator circuit or VCO110by the current source160at the mid tap of the oscillator circuit coil or inductivity210, a direct current potential or DC potential VCO_dc forms in dependence on the exact current value IVCO, the DC potential being in the order of the threshold voltages of the two NMOS transistors180,190. The DC potential VCO_dc here has a value of VCO-dc0. If the current IVCOis large enough, a permanent vibration or oscillation is generated in the oscillator circuit. As soon as an oscillation is present, the voltage VCO_dc drops.

As has already been discussed in the introductory sections of the present application, the output amplitude or amplitude Û of the oscillation of the VCO110is dependent on the frequency f, as the equation (10) has already shown.FIG. 3athus illustrates the dependence of the VCO amplitude Û of the oscillation of the VCO110as a function of the frequency f in a frequency range between a minimum frequency fminand a maximum frequency fmax. In this range of the VCO frequency, the VCO amplitude rises substantially linearly from a minimum value Ûminto a maximum value Ûmax. Here, the VCO amplitude behaviour shown inFIG. 3ais based on a constant current of the current source160(IVCO=const.).

In addition,FIG. 3billustrates the behaviour of the VCO amplitude in the case of a constant current of the current source160with respect to a variation of the temperature of the VCO110, as has already been indicated in the introductory sections of the present application. If the temperature of the VCO110is increased from a minimum temperature value Tempminup to a maximum temperature value Tempmax, the VCO amplitude Û falls substantially linearly from a maximum amplitude value Ûmaxto a minimum VCO amplitude value Ûmin. Therefore, inFIGS. 3aand3b, the output amplitude Û of the VCO110is represented above the frequency f and the temperature for the case that the VCO and/or the VCO core110has a constant current or such is impressed thereon.

With VCOs110covering a large frequency and temperature range, it is therefore advisable to pay special attention to the output amplitude Û as same, as has been shown, strongly depends on the respective operating conditions. In the case of providing the VCO110with a constant current IVCO, for a safe functioning of the overall circuit, it is mostly essential that the amplitude Û be selected large enough so that the subsequent circuit may be driven with respect to all operating states within the specification. In the case of mobile and therefore energy-critical systems having integrated circuits (ICs) in particular, this is a serious problem in providing a constant current IVCO. In order to maximize a battery lifetime or accumulator lifetime of such a battery-powered or accumulator-powered system, it has so far been essential to limit the specified operating range of the VCO110so that the amount of current or energy necessitated to maintain a minimum oscillation amplitude is not too large. In other words, the precision or stability of the oscillation amplitude determines the optimal efficiency of the battery energy or accumulator energy in the case of charging the VCO110with a constant current.

FIG. 4shows a further embodiment of the present invention in the form of an amplitude regulating circuit100with a voltage-controlled oscillator or VCO110having a structure that has already been discussed in the context of the VCO110inFIG. 2. For this reason, please refer to the respective sections of the present specification with respect to the VCO110in the context ofFIG. 2. The VCO or oscillator110also has an input for a supply signal being provided by a supply circuit120with a supply signal output. Here, the supply circuit120comprises a controllable or regulatable current source300which is connected to the supply signal output of the supply circuit120on the one hand and to a supply voltage terminal310providing a positive supply voltage Vdd to the current source300on the other hand. The current source300, in addition comprises a control input coupled to a control input of the supply circuit120and further to a first control signal output of a comparator circuit130.

Analogously to the embodiment shown inFIG. 1, in the amplitude regulating circuit100shown inFIG. 2, the input of the VCO110and the supply output of the supply circuit120are also coupled to a first input of the comparator circuit130. The same is connected to a non-inverting input of a comparator circuit320, which comprises the comparator circuit130. The comparator circuit320also comprises an output which is connected to the first control signal output of the comparator circuit130and therefore to the control input of the current source300. An inverting input of the comparator circuit320is connected to a second input of the comparator circuit130via a voltage source330providing a (constant) voltage value Vdiff.

As in the embodiment shown inFIG. 1, the second input of the comparator circuit130is coupled to a reference supply output of a reference supply circuit140. Like the supply circuit120, the reference supply circuit140also comprises a controllable or regulatable current source340, which is coupled to the reference supply output of the reference supply circuit140on the one hand and to a supply voltage terminal310providing a positive supply voltage Vdd to the current source340on the other hand. Furthermore, the current source340has a control input which is connected to the output of the comparator circuit320via the reference control input of the reference supply circuit140and the second control signal output of the comparator circuit130.

As the embodiment of the present invention shown inFIG. 1has already shown, in the embodiment in the form of an amplitude regulating circuit100also shown inFIG. 4, the reference supply circuit140is connected via the reference supply output to a reference circuit150comprising a series connection of a resistive element350with a resistance value R and a transistor360. More precisely, the resistive element350is connected to an input of the reference circuit on the one hand and to a drain terminal of the transistor360on the other hand. A source terminal of the transistor360is further connected to a reference potential terminal200. A gate input of the transistor360is also connected to the drain terminal of the transistor and therefore to the resistive element350.

As has already been discussed in connection with the two transistors180,190of the VCO110, the transistor360shown inFIG. 4may be, just like the transistors180,190, an n-channel field-effect transistor such as an NMOS transistor or an npn bipolar transistor. InFIG. 4, the three transistors180,190, and360are each plotted as (normally off) n-channel field-effect transistors, the two field-effect transistors180,190having an identical ratio of the channel width W to the channel length LKto an extent possible in the production process. In this case, the transistor360has a ratio of channel width to channel length double the ratio of the two transistors180,190. In other words, the transistor360has a ratio of channel width to channel length of 2 W/LK.

FIG. 4therefore shows an embodiment of an amplitude regulating circuit100for an oscillator in the form of a VCO110or a VCO core110, which for amplitude regulation is coupled to a regulation comprising the supply circuit120, the comparator circuit130, and the reference supply circuit140. The reference supply circuit140is, as has been discussed, connected to the reference circuit150.

Therefore, the amplitude regulating circuit100for an oscillator110, represented inFIG. 4, offers the possibility of a regulation maintaining on a constant level the oscillation amplitude or amplitude of the oscillator110across a large operating range of the VCO110and does not load the VCO signal or frequency signal, which may be tapped via one or both of the output terminals240-1,240-2of the VCO110. The fact that there is no load on the VCO signal due to the amplitude regulating circuit100is an important advantage of the present embodiment, especially in the case of high frequencies. Depending on the concrete implementation or terms of reference, the missing of a load on the output of the VCO is particularly advantageous with frequencies above the typical 10 MHz. With modern technologies in particular, this advantage explicitly shows in frequencies of approx. 500 MHz and more.

A further advantage of the present embodiment of an amplitude regulating circuit100is the fact that a high degree of regulation accuracy regarding the amplitude regulation may be achieved. This accuracy, which may also be referred to as matching, is achieved by generating the reference quantity for the regulation by means of the reference circuit150, which in the embodiment shown inFIG. 4is constructed similar to the VCO or VCO core110and has the same current density as far as the transistors180,190, and360are concerned.

As has already been explained in connection withFIG. 4, the regulation or the amplitude regulating circuit100for a VCO110comprising a cross-coupled pair of NMOS transistors180,190, and a parallel oscillator circuit is represented. This oscillator circuit comprises an inductivity or coil210with an inductivity value L, a controllable capacity220comprising one or more varactors or trim capacitances, and comprising a capacitance value Ctune, and a loss resistor230, which is in turn represented inFIG. 4by its reference value G. For the sake of simplification, all circuit losses of the VCO core110occurring are combined in this loss resistor230. The operating current IVCOprovided by the supply circuit120is fed at the mid tap or central tap of the oscillator circuit coil210.

Here, a direct current potential or DC potential with a value VCO_dc in the order of the threshold voltages of the normally-off NMOS transistors180,190is created in dependence on the exact current value IVCO. If the current IVCOis large enough, i.e., if it exceeds a value typical for the concrete implementation, a permanent oscillation is generated in the oscillator circuit. As soon as this oscillation is present, the voltage VCO_dc at the mid tap of the inductivity120drops in dependence on the amplitude of the oscillation. This tapping of the voltage VCO_dc may amount to up to 1 V, typically up to 200 mV and is the crucial point for the regulation of the amplitude of the oscillation of the VCO110. The voltage at the mid tap of the inductivity210, before the oscillation in the parallel oscillator circuit of the VCO110begins, is referred to as the voltage VCO_dc0.

In the embodiment of an amplitude regulating circuit shown inFIG. 4, therefore, the current IVCOrepresents the supply signal, which is provided to the oscillator110by the supply circuit120. As has already been explained, the supply signal in the embodiment shown inFIG. 4has a voltage value VCO_dc, which depends on the amplitude of the oscillation of the oscillator110. Thus, the voltage value of the supply current represents the electrical quantity of the supply signal in the amplitude regulating circuit100shown inFIG. 4.

The regulation of the embodiment of an amplitude regulating circuit100illustrated inFIG. 4is based on comparing the decreased voltage VCO_dc at the VCO110, present at the input of the VCO110in the case of an oscillation, to a reference voltage VCO_Ref, which is generated at least partially in the reference cell or reference circuit150.

As has already been explained, the reference circuit150comprises one or more NMOS transistors360which are, within the limits of the production tolerances that may be achieved, identical to the transistors180,190of the VCO110and therefore have the same current density as the VCO core110. The transistor360may be realized both as a single transistor and a parallel connection of two transistors. If the transistors180,190, and360are, as is illustrated inFIG. 4, (normally off) NMOS transistors, the two transistors180,190each having a channel width W and a channel length LK, the transistor360may be constructed out of two transistors identical to the transistors180,190in the case of a parallel connection of two transistors. In other words, the transistor360may be embodied in the form of a parallel connection of two transistors having a ratio of channel width to channel length of W/LK. If, however, the transistor360is embodied as a single transistor, it should have a ratio of channel width to length of 2 W/LKin order to achieve a current density that is substantially identical to the VCO core110. This configuration of the transistor360also provides conditions in the reference circuit150similar to those in the VCO110.

The necessitated maximum voltage drop Vdiff, which may occur at the mid tap of the inductivity210and/or the input of the VCO110with respect to the voltage value VCO_dc0, represents a constant voltage value and is represented and/or realized by a voltage source330of the comparator circuit130in the embodiment of an amplitude regulating circuit100shown inFIG. 4. In order to achieve a constant amplitude of the oscillation of the oscillator110, it does not suffice to simply provide the voltage drop Vdiffcaused by the voltage source330, but the resistive element350with the resistance value R, also referred to as the matching resistance, is also necessitated. The resistor or resistive element350adjusts the amplitude curve across the operating range of the VCO110, as will be explained further on. Therefore, a voltage value VCO_Ref having a value (VCO_dc+Vdiff) appears at the input of the reference circuit150and/or at the reference supply output of the reference supply circuit140in the operation of the VCO110.

In other words, the regulation realized in the context of the VCO amplitude regulation by the supply circuit120, the reference supply circuit140, and the comparator circuit130makes sure that the voltages at the inverting and non-inverting inputs of the comparator circuit320are identical. If, as is illustrated inFIG. 4, the voltage provided at the inverting input of the comparator circuit320is referred to as VCO_Ref, and if the voltage VCO_dc is applied at the non-inverting input of the comparator circuit320based on the connection of the comparator circuit130in the embodiment represented inFIG. 4, the regulation yields an equality within the typical accuracies of a respective comparator circuit320, so that the relation
VCO_ref=VCO_dc   (11)
is valid.

Thus,FIG. 5shows a plot of a VCO characteristic curve field with four VCO characteristic curves370-1,370-2,370-3, and370-4, which are exemplarily selected from the VCO characteristic curve field. InFIG. 5, the current value IVCOprovided by the current source300of the supply circuit120is plotted on the abscissa. On the ordinate of the plot represented inFIG. 5, the voltage VCO_dc appearing at the input of the oscillator or VCO110is plotted, the voltage VCO_dc being, due to the regulation realized by the comparator circuit130, identical to the reference voltage VCO_Ref.

The VCO characteristic curves370-1to370-4represented inFIG. 5, differ from one another, like the VCO characteristic curve not shown inFIG. 5, which may be located in between the four curves represented, in that they depend on further parameters. As has already been discussed in connection withFIGS. 3aand3b, these comprise not least the temperature and the frequency of the oscillation of the VCO110caused by the change of the controllable capacity220. Thus, the VCO characteristic curve370-1, for example, corresponds to a low temperature and/or a high frequency with respect to a medium temperature and a medium frequency of the VCO110. In contrast to that, the VCO characteristic curve370-4relates to a high temperature and a low frequency.

Furthermore, to each characteristic curve, i.e. to each operating state of the VCO110, which is characterized not least by the temperature of the VCO and the frequency realized by the adjustable capacity220, an amplitude of the oscillation of the VCO110is allocated. In the plot chosen inFIG. 5, dots having a substantially identical or equal amplitude are arranged on one or more straight lines. A corresponding reference straight line380is drawn inFIG. 5. Based on this property of the plot represented inFIG. 5and the properties of the VCO110or the oscillator110, the intersection points of the reference straight line380and the characteristic curves370-1to370-4correspond to dots with (essentially) the same amplitude of the oscillation of the VCO110for different operating parameters of the oscillator, i.e., for different temperatures and frequencies. Such a reference straight line380may, for example, be obtained by a (numerical) fit of a respective VCO characteristic curve field.

The reference straight line380thus obtained, may now be simulated and/or implemented in terms of circuit engineering with respect to the embodiment of an amplitude regulation circuit100shown inFIG. 4, by correspondingly adapting on the one hand the voltage value Vdiffof the voltage source330and on the other hand and the resistance value R of the resistive element350. As is indicated inFIG. 5, based on the voltage value VCO_dc0given essentially by the transistors180,190, and/or transistor360, the voltage value Vdiffof the voltage source330determines the intersection point of the reference straight line380and the ordinate of the representation shown inFIG. 5. The gradient of the reference straight line380is determined by the resistance value R of the resistive element350from the ratio of the change of the voltage value VCO_dc and the change of the current value IVCO. While the gradient of the output voltage of the reference cell150, which is also basically given by the reference straight line380, is determined by the resistance value R of the resistive element350, the absolute level of the output voltage of the reference cell150is determined by the voltage value Vdiffof the voltage source330and the voltage VCO_dc0, which is given by the threshold voltages of the transistors180,190,360involved.

Basically, thus an implementation of the transistor360in connection with the reference circuit150may be omitted if the respective voltage drop, i.e. substantially VCO_dc0, is considered in voltage provided by the voltage source330. Nonetheless, the implementation of the transistor360in connection with the reference circuit150is advantageous in the embodiment shown inFIG. 4through the fact alone that by the transistor360, the voltage drop VCO_dc0caused by the transistors180,190of the VCO110is simulated. This is true independently of the respective operating conditions, i.e., independently in particular of the temperature the VCO110is exposed to. In other words, one particular advantage of the embodiment shown inFIG. 4is the fact that the voltage source330must not take into consideration possible temperature influences on the voltage VCO_dc0.

A method for adapting the voltage value Vdiffof the voltage source330and for dimensioning the resistance value R of the resistive element350therefore comprises:

1. Determining a VCO characteristic curve field by measuring an amplitude of an oscillation of the VCO110and the voltage VCO_dc appearing at the input of the oscillator110in dependence on the current IVCOimpressed at the input of the oscillator110and other operating parameters such as the temperature and/or the frequency of the oscillator110, as far as the latter is controllable and/or adjustable.

2. Determining a reference straight line380by a (numerical) approximation of the VCO characteristic curve field.

3. Determining a resistance value R for the resistive element350and the voltage value Vdiffof the voltage source330, possibly in consideration of the voltage value VCO_dc0of the offset voltage or the zero point voltage or zero oscillation voltage caused by the two transistors180,190of the oscillator110by means of the gradient of the reference straight line380and the intercept and/or the absolute term of the mathematical representation of the reference straight line380.

4. Configuring or trimming the resistive element350and the voltage source330so that same comprise the resistance value R and the voltage value Vdiff.

Depending on the accuracy necessitated, the last point in particular of the method described above may be carried out in advance for a complete series production, wherein in this case the obtainable accuracy of the amplitude regulation falls short of individual trimming of single oscillators110and their amplitude regulating circuits100for the benefit of simpler and faster production and therefore less production costs. In this case, the voltage source330and the resistive element350may be designed such as early as during the dimensioning and configuring of the amplitude regulation that same nominally and/or in the production series average have the voltage value Vdiffand the resistance value R.

Alternatively or in addition, for example, in order to achieve higher accuracy of the amplitude regulation, an amplitude regulating circuit100and/or the entire integrated circuit, which comprises the oscillator110and the amplitude regulating circuit100, may be adjusted to values as optimal as possible by a conditioning and/or trimming process. In this case, the resistive element350would be adjusted with respect to its resistance value R during fourth step of the above method, for example, by means of a doping step, a change in a width of a conductive trace of the resistive element350, or any other process by which an electrical resistance value of a resistive element, produced, for example, in semiconductor technology, may be influenced. Exemplarily, a resistive semiconductor element on the basis of a polysilicon layer may be embodied, which may be adapted with respect to its width by the use of an etching process and/or radiation by means of a laser or a focusing ion beam. Hereby, the concrete resistance value R of the resistive element350may be adapted to the VCO characteristic curves370-1to370-4, which in this instance are experimental.

The same applies to the voltage source330that may be realized, for example, by providing the same by means of a voltage divider, relating to an external supply voltage. Hereby, the problem of an adjustable voltage source330is also traced back to adjusting or trimming resistive elements, as has been discussed above.

InFIG. 5, therefore, the curve of the reference voltage VCO_Ref is illustrated in the form of the reference straight line380above the current IVCOof the current source300. Therefore, based on the amplitude regulation, the following connection is yielded for the reference voltage VCO_Ref in the steady state of the VCO110:
VCO_Ref=VCO_dc0+R·IVCO−Vdiff=VCO_dc  (12).

Here, as has been discussed above, the VCO_dc0is the voltage forming at the NMOS transistor(s)180,190,360when the current IVCOpasses through them and there is no oscillation present at the output terminals240-1,240-2of the VCO110.

In addition, inFIG. 5, the characteristic curve field is illustrated with four exemplary VCO characteristic curves370-1to370-4of the VCO110for various operating ranges. The intersection points of the characteristic curve field with the reference straight line380yield the operating points of the regulation, which adjust in a stable manner depending on the respective load. This is feasible as the dots for a constant amplitude are situated approximately on a straight line in the VCO characteristic curve field. It is therefore possible to operate with a reference circuit150, as is shown by the embodiment illustrated inFIG. 4, and to design the regulation correspondingly by means of respective dimensioning of the switching elements involved.

The regulation in the embodiment shown inFIG. 4can therefore be changed via two quantities, once via the resistance value R of the resistive element350and then via the constant voltage value Vdiffof the voltage source330. Therefore, the amplitude height or the amplitude and its curve may be adjusted over the respective cases of loading and maintained constant by means of the amplitude regulating circuit100.

The function of this regulation with the help of the reference circuit150, which is constructed substantially matching the VCO core110, i.e. substantially has the same transistors and the same current densities at, could be operated by means of a (numerical) simulations on a realistic VCO circuit. Therefore,FIG. 6ashows a comparison of several curves of the amplitude of an oscillation as a function of the temperature in a temperature range from −50° C. to 150° C. for various frequencies, which were realized by correspondingly adjusting the capacity220. More precisely,FIG. 6ashows the result of a corresponding simulation with respect to the amplitude above the temperature in various frequency bands, wherein the curves390show a flat course of approx. 500 mV in the range of the VCO amplitude adjusted in the case of the regulation enabled and/or with a regulation. In good approximation, with the help of the amplitude regulation circuit100, the amplitude of the oscillation may be kept constant with very good accuracy in various frequency ranges in a large temperature range of 200° C. The curves400correspond to an operation of the VCO110in the case of a constant current IVCO, i.e., an operation of the VCO110without regulation. Here, the curves400show that the amplitude strongly depends on the temperature and the frequency. In other words, the curves400scan a large area in the case of a constant current provision. An arrow410indicates the direction of a rising frequency for the curves400.

FIG. 6bshows the resulting VCO current IVCOas a function of the temperature for various frequency bands for the parameters already shown inFIG. 6a. While the curves420shown inFIG. 6b, are based on a constant VCO current of approx. 3 mA and correspond to the amplitude curves400ofFIG. 6a, i.e. the case of an operation of the VCO110without any regulation, the VCO current curves430relate to the case of the amplitude of the oscillation of the VCO110being regulated. Here, too, an arrow440shows the direction of the rising frequency the curves430are based on.

While6ashows that the curves400of the amplitude without regulation significantly decrease as the temperature rises, asFIG. 3bhas already shown, an embodiment of an amplitude regulating circuit makes it possible to keep the amplitude of the oscillation of the VCO110fixed very well across a very large temperature range of 200° C. as it may occur, for example, in the automobile industry. In contrast to that, the curves400drop significantly in the temperature range between −50° C. and 150° C. as the temperature rises. As, as has already been explained, the curves400of the amplitude correspond to the VCO current curves420, the illustration inFIGS. 6aand6bin addition provides a direct comparison of the energy consumption of the VCO110in the cases with and without regulation by the amplitude regulating circuit100. The VCO current of approx. 3 mA, which the curves420also show, is rated such that the resulting amplitude of the VCO110does not drop to a value below approx. 500 mV with respect to the temperature and frequency in the parameter range shown inFIGS. 6aand6b.

As the curves390of the amplitude correspond to the curves430of the VCO current, and as the curves390are all in the range of approx. 500 mV, resulting energy savings may be read from a direct comparison of the VCO currents with and without regulation. Therefore, although the curves430of the VCO current exhibit increasing current requirements as the frequency drops and the temperature rises, their magnitude will be below the current curves420, with the only exception of the case of the lowest frequency and the highest temperature.

In other words,FIG. 6bshows that in the optimum case up to 2.2 mA may be saved with respect to the 3 mA when the amplitude is regulated to approx. 500 mV with the help of the amplitude regulating circuit100, as in the case of low temperatures and a high frequency only approx. 600 μV or 0.6 mA are necessitated to ensure this amplitude. In other words,FIGS. 6aand6bshow that, compared to a constant current provision, an embodiment of an amplitude regulating circuit according to the present invention may significantly reduce the energy consumption or energy requirements of a VCO110in general. In addition, as the output of the VCO110in the form of the output terminals240-1,240-2is not loaded in the embodiments of the present invention, which is advantageous particularly in the field of high frequencies, the embodiments of the present invention are advantageous also compared to controlled core currents with a trimming or regulation in the case of signal loading.

Embodiments of the present invention in the form of amplitude regulating circuits therefore enable an amplitude regulation for voltage-controlled oscillators with a large frequency range, which are also referred to as wide-band VCOs. A respective amplitude regulating circuit according to an embodiment of the present invention may, for example, be employed in connection with products having integrated VCOs as may be found, for example, in the field of radio transmitters and/or radio receivers that are battery-powered or accumulator-powered.

As has already been explained in the context of the discussions regarding the various embodiments of the present invention, the reference supply circuit140and the reference circuit150are adapted to the supply circuit120and the oscillator110such that a signal strength or an electrical reference quantity of the reference supply signal has a predetermined ratio to the signal strength or the electrical quantity of the supply signal. As in the embodiment shown inFIG. 4in particular, both the reference supply signal and the supply signal are currents having respective current values, the current value of the current source340and the current value of the current source300have a predetermined ratio to each other, which is, in the embodiment shown inFIG. 4, identical currents or equal currents, as both current sources300,340supply a current value IVCOeach. This also forms the basis of the relation of the reference voltage VCO_Ref in equation (12). In the context of the present application, equal or identical currents and signal strengths are understood as ones differing from one another by not more than a typical +/−25% and advantageously not more than +/−10%.

Basically, other predetermined ratios may also be used. In the case of the embodiment shown inFIG. 4, the current source340of the reference supply circuit140may output a correspondingly smaller current value with respect to the current value of the current source300of the supply circuit120, if the resistance value R of the resistive element350is increased to the same degree. In other words, the current of the current source340of the reference supply circuit140may be reduced as long as a voltage drop across the resistive element350remains substantially constant in the embodiment shown inFIG. 4. Moreover, in the case of reducing the current strength of the current source340, the transistor360of the reference circuit150, too, may be dimensioned correspondingly smaller, as long as the ratio of the channel width to the channel length corresponds to that of the parallel connection of the two transistors180,190of the VCO110. Accordingly, as a rule, the current value of the current source340may of course be increased, which would, however, lead to increased energy consumption of the overall circuit, which is normally not desired.

In addition, voltage sources may also be employed as the supply circuit120and the reference supply circuit140if the oscillator110correspondingly reacts by changing the current value at its input when the amplitude of the resulting oscillation changes.

Depending on the conditions, embodiments of the inventive method may be implemented in hardware or software. The implementation may be effected on a digital storage medium, particularly a floppy disc, CD or DVD, with electronically readable control signals, which may cooperate such with a programmable computer system that embodiments of the inventive methods are configured. In general, therefore, embodiments of the present invention also consist in a software program product or a computer program product or a program product with a program code stored on a machine-readable carrier for performing an embodiment of the inventive method if the software program product is run on a computer or a processor. In other words, an embodiment of the present invention may therefore be realized as a computer program or a software program or a program with a program code for performing an embodiment of the method if the program is run on a processor. The processor may be formed by a computer, a chip card (smart card) or any other integrated circuit.