Abstract:
A frequency divider, which has a cross-coupled inductor-capacitor (LC) structure or a ring structure, is inputted with a direct current (DC) control voltage from an input terminal. By doing so, the frequency divider can adjust an oscillation frequency; and further compensate the input power sensitivity, lower the power consumption and increase the division range. The frequency divider can be used in high-band/high-speed digital or analog communication systems.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a frequency divider; more particuiarly, relates to, without changing a circuit structure, ad justing an oscillation frequency to obtain a compensation to a power sensitivity of an input, to reduce a power consumption of the input and to increase a frequency range for division.  
       DESCRIPTION OF THE RELATED ARTS  
       [0002]     A general injection locked frequency divider has a structure of an oscillator, an LC structure or a ring structure, where signals are injected from an in injection terminal. When an injected signal has a phase synchronization to an inner oscillation signal, a division is done. The operative frequency of the circuit is decided by an oscillator, where the power required is low enough to be used in circuits with low power. Such a circuit is characterized in a big division ratio, a small locked frequency and a small phase noise.  
         [0003]     Generally speaking, the injection locked frequency divider has a smaller locked frequency than that of a static frequency divider so that an operation under a frequency deviated from the oscillation frequency requires an increased input signal power level to get a correct state of a division. Yet, regarding the operation under the deviated frequency, because the inner oscillating signal is no more synchronization with the input signal, a division is impossible even through the power level of the input signal is increased. Therefore, the injection locked frequency divider is only suitable for narrow-band communication systems with low transferring rates.  
         [0004]     A prior art is proclaimed in Taiwan, called “A frequency divider circuit”, where a multi-phase signal according to an input signal is outputted and the outputted signal has a frequency obtained by equally dividing a period (integer) of the frequency of the in put signal. The prior art comprises an N-stage ringed-amplifier circuit and a current-deviation modulator circuit, where the current-deviation modulator circuit produces an alternating current having the same frequency as that of the input signal. Then the alternating current is injected into the ringed-amplifier circuit to obtain a fixed oscillation frequency. After the ringed-amplifier circuit obtains a state of a steady oscillation, an output terminal of the ringed-amplifier circuit outputs a signal equally dividing the period and the frequency is a 1/N part of the reference frequency.  
         [0005]     Another prior art is revealed in Taiwan, named “A frequency divider”, comprising a divider to produce a first clock and a second clock according to an input clock; a switching device to out putting an output clock of the first clock upon an input switching signal of a first state, or of the second clock upon an output switching signal of a second state; and a switching control device to produce the input or output switching signal for the first state or the second state and to output the input or output switching signal to the switching device according to the frequency of the output clock from the switching device.  
         [0006]     Although the prior arts have the frequency-division function, the ranges for frequency division are narrow. For a wider range for frequency division, a bigger input power or a change in circuit structure is required. Hence, the prior arts do not fulfill users&#39; requests on actual use.  
       SUMMARY OF THE INVENTION  
       [0007]     The main purpose of the present invention is to ad just an oscillation frequency by in putting a DC control voltage without changing the circuit structure to maintain a lowest power strength of an in put signal, to reduce a power consumption of the input signal and to increase the frequency range for dividing the input signal.  
         [0008]     To achieve the above purpose, the present invention is a high frequency divider with input-sensitivity compensation, comprising an input terminal, an injection transistor, a first inductance, a second inductance, a first transistor, a second transistor, a third transistor, a fourth transistor, a first output buffer, a second output buffer, a first output terminal, a second output terminal, and a voltage control terminal, where the above components are connected electrically to form a cross-coupled LC structure; a DC control voltage is inputted from the voltage control terminal to change capacities of the third transistor and the fourth transistor to adjust an oscillation frequency. Or, the frequency divider can be comprised of a plurality of inverters, an input terminal, an injection transistor, an output buffer, an output terminal and a voltage control terminal, where the above components are connected electrically to form a ring structure; the inverter comprises a fifth transistor, a sixth transistor and a seventh transistor connected electrically; a DC control voltage is inputted from the voltage control terminal to change an RC time of each inverter to adjust an oscillation frequency. Accordingly, a novel high frequency divider with input-sensitivity compensation is obtained.  
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0009]     The present invention will be better understood from the following detailed descriptions of the preferred embodiments according to the present invention, taken in conjunction with the accompanying drawings, in which  
         [0010]      FIG. 1  is a structural view showing a first preferred embodiment according to the present invention;  
         [0011]      FIG. 2A  is a structural view of the second preferred embodiment;  
         [0012]      FIG. 2B  is a structural view of the inverter;  
         [0013]      FIG. 3  is a view showing a range of input sensitivity for the frequency division under a fixed oscillation frequency;  
         [0014]      FIG. 4  is a view showing the relation between the DC control voltage and the oscillation frequency obtained thereby; and  
         [0015]      FIG. 5  is a view showing a range of spectrum for the frequency division with an adjusted oscillation frequency. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     The following descriptions of the preferred embodiments are provided to understand the features and the structures of the present invention.  
         [0017]     Please refer to  FIG. 1 , which is a structural view showing the first preferred embodiment according to the present invention. As shown in the figure, the present invention is a high frequency divider with input-sensitivity compensation, comprising an input terminal  11 , an injection transistor  12 , a first inductance  131 , a second inductance  132 , a first transistor  141 , a second transistor  142 , a third transistor  151 , a fourth transistor  152 , a first output buffer  161 , a second output buffer  162 , a first output terminal  171  (out+), a second output terminal  172  (out−), and a voltage control terminal, where the above components are connected electrically to form a cross-coupled inductor-capacitor (LC) structure.  
         [0018]     Each transistor  141 ,  142 ,  151 ,  152  in the components is a metal oxide semiconductor (MOS) transistor, a high electron mobility transistor (HEMT), a bipolar junction transistor (BJT) or a heterojunction bipolar transistor (HBT). The third transistor  151  and the fourth transistor  152  are va varactors or diodes. The first inductance  131  and the second inductance  132  are spiral or curved (meander type). And the first output buffer  161  and the second output buffer  162  both have a structure of an emitter-coupled logic (ECL), a common mode logic (CML), a positive-ECL (PECL) or a low voltage differential signaling (LVDS) circuit.  
         [0019]     The frequency divider  1  according to the present invention is an injection locked frequency divider with a cross-coupled LC structure. The frequency divider  1  can be an oscillator. A direct-current (DC) control voltage is inputted from the voltage control terminal  18  into the third transistor  151  and the fourth transistor  152  to change capacities of the third transistor  151  and the fourth transistor  152 . A first transistor  141  and a second transistor  142  are used coordinately with negative impedances to eliminate positive resistances of the first inductance  131  and the second inductance  132 . Thus, an oscillation frequency is obtained from the frequency divider  1 . By doing so, before inputting any signal, the frequency divider  1  obtains an oscillation frequency through inputting a DC control voltage for an adjustment in advance. Then, the oscillation frequency can be adjusted under different levels by controlling the DC control voltage.  
         [0020]     In the other hand, an input signal for frequency division is inputted from the input terminal  11 , whose frequency is an even times to the oscillation frequency of the frequency divider  1 . After the division, the frequency-divided input signal is amplified by the first output buffer  161  and the second output buffer  162  to be outputted from the first output terminal  171  and the second output terminal  172 , where the outputted divisor of the frequency divider  1  is an even number.  
         [0021]     But, if the frequency of the input signal is deviated from the oscillation frequency and therefore is not divided, a DC control voltage is in inputted from the voltage control terminal  18  to change the capacities of the third transistor  151  and the fourth transistor  152  to further adjust the oscillation frequency into a reciprocal of an even times of the frequency of the input signal.  
         [0022]     Please refer to  FIG. 2A  and  FIG. 2B , which are structural views of the second preferred embodiment and the inverter. As shown in the figures, the present invention is a high frequency divider with input-sensitivity compensation, comprising a plurality of inverters  19 , an input terminal  11   a , an injection transistor  12   a , an output buffer  161   a , an output terminal  171   a  and a voltage control terminal  18   a , where the inverters  19  are connected serially and the components are connected electrically to obtain an injection locked frequency divider  1   a  with a ring structure.  
         [0023]     The plurality of inverters  19  has an odd number of inverters; and each inverter  19  comprises a fifth transistor  191 , a sixth transistor  192  and a seventh transistor  193  connected electrically, where the fifth transistor  191  and the sixth transistor  192  are inverters to obtain RC time; and the seventh transistor  193  is a delay-time adjusting transistor. By inputting a DC control voltage to each inverter  19  from each voltage control terminal  18   a  to change the RC time, the oscillation frequency is changed into a reciprocal of an even times of frequency of an input signal so that a compensation to an input power sensitivity is obtained.  
         [0024]     Please refer to  FIG. 3 , which is a view showing a range of input sensitivity for the frequency division under a fixed oscillation frequency. As shown in the figure, a first sensitivity curve  3  shows a frequency range between 3 GHz (gigahertz) and 5 GHz for the input signal to be divided when the oscillation frequency is 2 GHz. When the input signal has a frequency of 4 GHz, which is 2 times (an even times) to the oscillation frequency, the input signal can be divided with a smallest power sensitivity (−30 dBm).  
         [0025]     Please refer to  FIG. 4 , which is a view showing the relation between the DC control voltage and the oscillation frequency obtained thereby. As shown in the figure, the curve  4  shows that the frequency divider according to the present invention ad adjusts an oscillation frequency by inputting a DC control voltage from the voltage control terminal. The oscillation frequency changes according to the value of the DC control voltage. Such as, a DC control voltage of 0.4 volt (V) being inputted obtains an oscillation frequency between 2.0 GHz and 2.25 GHz; a DC control voltage of 0.6V being inputted obtains an oscillation frequency between 1.75 Hz and 2.0 GHz.  
         [0026]     Please refer to  FIG. 5 , which is a view showing a range of spectrum for the frequency division with an adjusted oscillation frequency. As shown in the figure, with an oscillation frequency of 2 GHz and an output divisor of 2, a frequency between 3 GHz and 5 GHz is required for an input signal to be divided (as shown by a second spectrum curve  5 ). When the frequency for an input signal is 4 GHz, which is 2 times to the oscillation frequency, the required power sensitivity for the input signal is −30 dBm. And when the frequency of the input signal is greater than or smaller than the oscillation frequency, the oscillation frequency can be adjusted into a half of the frequency of the input signal to maintain the function of frequency division. For example, when the oscillation frequency is 2 GHz and the frequency of the input signal is 5 GHz, the oscillation frequency can be ad adjusted into 2.5 GHz (as shown by a third spectrum curve  5   a ) as a half of the oscillation frequency so that the power sensitivity of the input signal remains −30 dBm as a compensation to the power sensitivity.  
         [0027]     To sum up, the present invention is a high frequency divider with input-sensitivity compensation, where, without changing the circuit, a DC control voltage is controlled to adjust an oscillation frequency so that a power sensitivity of the input signals is lowered, the consumption of input power is reduced and the frequency range for division is increased.  
         [0028]     The preferred embodiments herein disclosed are not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.