Abstract:
A power detector for measuring the power transfer between a circuit for emitting an electrical signal and a first conductor that receives the emitted electrical signal. The emitted signal causes a magnetic field to be generated in the first conductor. A coupling detection circuit measures an electric current that arises in a second conductor that is proximate and electrically coupled to the first conductor. The measured electric current in the second conductor is used to determine the power transfer between the emitting circuit and the first conductor. The first and second conductors can be bond wires within an integrated circuit package, and the coupling detection circuit can be disposed in a semiconductor substrate within the integrated circuit package.

Description:
FIELD OF THE INVENTION 
   This invention relates to the area of measuring of power coupling and more specifically to the area of measuring power coupling between a circuit and a load using induced current flow. 
   BACKGROUND OF THE INVENTION 
   Power amplifiers (PAs) are used to amplify an input signal prior to providing an amplified output signal to a load. For instance, PAs are used for RF applications, where the PAs are typically coupled to an antenna arrangement. In other cases, PAs are for example used for delivering the amplified signal to a speaker. 
   In delivering power from the PA to a load coupled thereto, an impedance match between the PA, coupling circuit and the load is important in order to facilitate maximum power transfer therebetween. Transferring less then the maximum power results in unnecessary energy consumption by the PA, since this extra energy not transferred is lost. For instance, when antennas are coupled to PAs, then proper impedance matching is preferable because maximum power transfer occurs therebetween. 
   A Voltage Standing Wave Ratio (VSWR) is used for antenna systems to measure the coupling efficiency between the PA and the antenna arrangement. Typically, most antennas are not directly connected to the PAs. The antenna is usually located some distance from the transmitter, in the form of a PA, and requires a feedline, in the form of a coupling circuit, to transfer power therebetween. If the feedline has no loss, and is impedance matched to both the PA output impedance and the antenna input impedance, then maximum power is delivered to the antenna. In this case the VSWR is 1:1 and the voltage and current are constant over the whole length of the feedline. Any deviation from this situation causes a “standing wave” of voltage and current to exist on the feedline therebetween. This standing wave results in energy used for driving the PA to be wasted and thus leads to system inefficiencies. 
   Measuring of the VSWR is typically performed using voltage detectors disposed within the PA. Unfortunately, voltage detectors do not take into account load mismatching between the power amplifier and a device coupled thereto. Therefore, coupling values obtained using the voltage detectors may not be representative of actual coupling therebetween. As a result, reliable values for the VSWR may not be provided. 
   A need therefore exists for a way of measuring power coupling between a PA and a load that uses other than voltage detectors. It is therefore an object of the invention to provide a method of measuring power coupling between a circuit for emitting an electrical signal and a load coupled thereto by using induced current flow. 
   SUMMARY OF THE INVENTION 
   In accordance with the invention there is provided a power detector for measuring power transfer between a circuit for emitting an electrical signal and a first load for receiving the electrical signal comprising: a first conductor for having a magnetic field generated thereabout in response to propagation of the electrical signal therein; a second conductor disposed in proximity of the first conductor, the first and the second conductors disposed having a coupling length therebetween; and, a coupling detection circuit electrically coupled to the second conductor, the coupling detection circuit for receiving an electric current representative of power transfer between the circuit and the first load induced to flow in the second conductor in response to the coupled magnetic field and for measuring power transfer between the circuit for emitting an electrical signal and the first load. 
   In accordance with the invention there is provided a power detector for measuring power transfer between a circuit for emitting an electrical signal and a first load for receiving the electrical signal comprising: a first conductor coupled to a first output port of the circuit; a second conductor coupled to a second output port of the circuit, the first and second conductors for each having a magnetic field generated thereabout in response to propagation of the electrical signal therein; a third conductor disposed in proximity of the first conductor; a fourth conductor disposed in proximity of the second conductor, the third and fourth conductors disposed each having a coupling length therebetween; and, a coupling detection circuit having first and second input ports electrically coupled to the third and fourth conductors, respectively, the coupling detection circuit for receiving an electric current in each conductor coupled thereto, the electric current representative of power transfer between the circuit and the first load induced to flow in the third and fourth conductors in response to the coupled magnetic field and for measuring power transfer between the circuit for emitting an electrical signal and the first load. 
   In accordance with the invention there is provided a method of measuring power transfer between a circuit for emitting an electrical signal and a first load for receiving the electrical signal comprising the steps of: providing the electrical signal within a conductor to drive the first load; magnetically coupling a radiated portion of the electrical signal to a second other conductor, the second other conductor other than forming part of the first load; providing the magnetically coupled signal to a detector for measuring thereof; and, determining power transfer between the circuit and the first load in dependence upon the measured magnetically coupled signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the drawings in which: 
       FIG. 1  illustrates a prior art microstrip parallel line coupler in the form of first and second parallel microstrip lines and disposed on a same substrate; 
       FIG. 2  illustrates a cross-sectional view of the prior art microstrip parallel line coupler; 
       FIG. 3   a  illustrates even mode propagation in the prior art microstrip parallel line coupler; 
       FIG. 3   b  illustrates odd mode propagation in the prior art microstrip parallel line coupler; 
       FIG. 4   a  illustrates an embodiment of the invention, a dual bond-wire power coupler; 
       FIG. 4   b  outlines operating steps in accordance with embodiments of the invention shown in  FIGS. 4   a ,  5  and  6 ; 
       FIG. 5  illustrates another embodiment of the invention, a four bond-wire power coupler; and, 
       FIG. 6  illustrates yet another embodiment of the invention, a four circuit trace PCB power coupler. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   When two transmission lines are close enough together, then it is possible to couple power between the transmission lines. The coupling of power is a result of interactions between electromagnetic fields from each transmission line. To those of skill in the art it is known that power can be coupled between microstrip lines, as is disclosed in the reference found at Bilkent University, Department of Electrical and Electronics Engineering, in the microwave problems and tutorials section, within the EM applications section, entitled “Directional Coupler Design &amp; Analysis,” incorporated herein by reference. 
   Referring to prior art  FIG. 1 , a microstrip parallel line coupler  100  is shown, in the form of first and second parallel microstrip lines  101  and  102  disposed on a same substrate  103  having a ground plate thereunder. The first microstrip line  101  has a first input port  101   a  and a first output port  101   b  and the second microstrip line  102  has a second input port  102   a  and a second output port  102   b . The first and second parallel microstrip lines have a coupling region therebetween, designated as  105 . 
   To those of skill in the art it is known that microstrip transmission lines do not support quasi transverse electric modes (TEM) of operation. Furthermore, those of skill in the art appreciate that parallel line couplers have both odd and even modes of operation. The odd and even modes provide the microstrip parallel line coupler  100  with an even mode impedance (Z oe ) and an odd mode impedance (Z oo ). Additionally, each microstrip line has a microstrip line impedance (Z o ). Odd and even modes for the microstrip parallel line coupler  100  are shown in prior art  FIGS. 3   a  and  3   b , respectively. 
   A cross-sectional view of the prior art microstrip parallel line coupler  100  is shown in prior art  FIG. 2 . In terms of analyzing the operation of the coupler shown in prior art  FIG. 1 , the following design parameters are important: a width of each microstrip line (w)  203 , a height of the substrate (h)  201 , and a separation between the microstrip lines (s)  202 . Furthermore, other parameters that are of importance are the relative dielectric constant of the substrate (ε r ) and the effective permittivity (ε eff ), as well as coupling (C) between the parallel microstrip lines. From the aforementioned parameters, a shape ratio w/h and a spacing ratio s/h are determined for coupling between the parallel microstrip lines  101  and  102 . 
   Of course, the shape ratios only deal with the cross-sectional parameters of the microstrip parallel line coupler  100 . However, as is seen in prior art  FIG. 1 , microstrip parallel line coupler  100  also has another parameter, length. In determining an optimum length of the microstrip parallel line coupler  100 , a predetermined design frequency is chosen and the length is determined accordingly using this design frequency. In this case, for the purposes of improved coupling between microstrip lines, a length of λ/4 is chosen. 
   Power detectors that are currently implemented on power amplifiers are essentially voltage detectors. Unfortunately, voltage detectors do not take into account load mismatching between the power amplifier and a device coupled thereto. Thus, a variation of the microstrip parallel line coupler  100  is used to facilitate more accurate measuring of power coupling. An example of this variation is shown in  FIG. 4   a  as an embodiment of the invention. 
   Referring to  FIG. 4   a , a semiconductor die  701  disposed within a semiconductor package  702  is illustrated. Bonding wires  703   a  through  703   b  are provided for connecting ports disposed on the semiconductor die to pins  704   a  through  704   c  at an outside thereof. Disposed within the semiconductor die  701  are an amplifier circuit  705  and a coupling detection circuit (CDC)  706 . The amplifier circuit output port is connected to the bond wire  703   b . Bond wires  703   a  is in proximity of bond wire  703   b  and preferably adjacent and preferably substantially parallel thereto. Of course, pin  704   a  is preferably of such a design that it does not penetrate the semiconductor package, but serve as a terminating point for the bond wire and is connected to an impedance (Z o )  709   a.    
   Referring to  FIG. 4   b , method steps are outlined detecting induced current flow in an electrical conductor in accordance with an embodiment of the invention. As electrical energy flows from the amplifier  705  through bond wire  703   b , a magnetic field is induced about the bond wire in response to electrons flowing through the bond wire  703   b . Because bond wire  703   a  is in close enough proximity to bond wire  703   b , an electric field is induced to flow in this adjacent bond wire  703   a . The CDC  706  detects this electric current and a determination is made as to an amount of electrical energy flowing through bond wire  703   b . A coupling length  708  between the bond wires  703   a  and  703   b  determines an amount of energy coupling therebetween. Preferably, along this coupling length  708  the bond wires are sufficiently close and sufficiently parallel to facilitate coupling of energy therebetween. 
   Of course, those skilled in the art appreciate that if a power amplifier, such as amplifier  705 , is misterminated at the output port thereof, a standing wave is generated between the amplifier output port and an input port of a device  707  coupled thereto. Having proper termination results in maximum power transfer between the amplifier  705  and the device  707  coupled thereto. Typically, if the power amplifier output port is misterminated, then an impedance of the input port of the device  707  and coupling circuit, coupling the device  707  to the amplifier output port, does not match the impedance of the amplifier output port. This impedance mismatch results in improper power transfer from the amplifier to the device  707 . This results in a standing wave to be generated along bond wire  703   b . This standing wave causes electrical energy to be induced in bond wire  703   a  through electromagnetic coupling occurring mostly along the coupling length  708  therebetween. An amount of electrical energy flowing in this bond wire  703   a  is related to the amount of impedance mismatch between the amplifier circuit output port and the device  707 . Thus, the higher the impedance mismatch between the amplifier output port and the input port of the device, the more electrical energy is provided to the CDC  706 . Conversely, having properly terminated coupling between the circuit  705  and the device  707  results in a minimal amount of electrical energy to be detected by the CDC  706 . 
   Detecting the magnetic field about the bond wire that delivers the signal to the device coupled thereto advantageously allows for monitoring of the radiated power. Of course, the more power that is radiated by bond wire  704   b , the less efficient the power transfer between the amplifier and device coupled thereto. Sensing of output voltage between the power amplifier and device coupled thereto is unfortunately not representative of the power transfer occurring therebetween, thus measuring of radiated power advantageously allows for more accurate measurements of power coupling. 
   In  FIG. 5  a variation of the embodiment shown in  FIG. 4   a  is illustrated. In this case, a semiconductor die  801  disposed within a semiconductor package  802 . Bonding wires  803   a  through  803   d  are provided for connecting ports disposed on the semiconductor die  801  to pins  704   a  through  704   d  at an outside thereof. Disposed within the semiconductor die  801  are an amplifier circuit  805  having two output ports and a coupling detection circuit (CDC)  706 . Each of the amplifier circuit  805  output ports is connected to a respective bond wire  803   b  and  803   c . Bond wire  803   a  is in proximity to bond wire  803   b  and preferably adjacent and preferably substantially parallel thereto. Bond wire  803   d  is in proximity to bond wire  803   c  and preferably adjacent and substantially parallel thereto. Of course, pins  704   a  and  704   d  are preferably of such a design that they do not penetrate the semiconductor package, but serve as a terminating point for their respective bond wire, with each terminated to a respective impedance  709   a  and  709   d . As electrical energy flows from the amplifier  805  through bond wires  803   b  and  803   c , a magnetic field is induced about each of the bond wire in response to electrons flowing therethrough. Because bond wires  803   a  and  803   d  are in proximity to bond wires  803   b  and  803   c , an electric field is induced to flow in these adjacent bond wires  803   a  and  803   d . The electric field is induced along a coupling length  808   a  and  808   d , where preferably the bond wires are substantially parallel along this length and are sufficiently close to facilitate partial energy transfer therebetween. The CDC  706  detects this induced electric current and a determination is made as to an amount of radiated electrical energy that is lost in the coupling between the amplifier circuit and the device coupled thereto. The more electrical energy that is detected by the CDC, meaning the more energy that is radiated, the worse the coupling between the circuit  706  and the device  807  and as a result, the worse the power transfer therebetween. 
   In  FIG. 6 , a further variation of the embodiment of the invention is shown. In this case a circuit board  901  is provided with dual circuit traces  903   b  and  903   c  electrically coupled to output ports of an amplifier circuit  905  disposed within an integrated circuit  902 . Two additional circuit traces  903   a  and  903   d  are in proximity thereof and preferably adjacent to each of the dual circuit traces  903   b  and  903   c , respectively. The additional circuit traces  903   a  and  903   d  are coupled to an on-chip CDC  706  at an end thereof, and at an opposite end thereof are coupled to a respective impedance  909   a  and  909   d . The dual circuit traces  903   b  and  903   c  are further electrically coupled to a device  807  that acts as a load. 
   The two additional circuit traces  903   a  and  903   d  are preferably substantially parallel to traces  903   b  and  903   c  and sufficiently close thereto and have a sufficient coupling length  908   a  and  908   d  therebetween to facilitate coupling of radiated energy induced by traces  903   b  and  903   c . Thus, when the impedance of the amplifier circuit output ports does not match the input impedance of the device, then maximum power transfer does not occur therebetween and electrical energy is induced in traces  903   a  and  903   d . The CDC is coupled to traces  903   a  and  903   d  using pins disposed on the chip  902 . Having the CDC within the same chip as an amplifier circuit facilitates the determining of whether maximum power transfer is occurring between the amplifier circuit and the device. This advantageously allows for active monitoring of the power transfer between the amplifier and the device and allows for performance of the amplifier circuit to be modified, in response to the CDC, in order to facilitate improved power transfer therebetween. 
   Advantageously, packaging of the semiconductor die is repeatable in those embodiments shown in  FIGS. 7 and 8 , thus the power coupler performance is repeatable too. Of course, it may be preferable to calibrated the CDC for each different packaged semiconductor die to ensure that readings derived from the CDC are deterministic of the actual power coupling between the amplifier circuit and the device. 
   Preferably, the bond wire lengths  703   a  through  703   c  and  803   a  through  803   d  are approximately 1 mm in length, however this length is not that important. Of course, the length of the bond wires determines an amount of coupling therebetween. Typically, a signal level provided to the CDC from the bond wires is around 30 dB smaller than an amplified signal emitted from output ports of the amplifier circuit. 
   Of course, the CDC is used to determine power coupling between the circuit and the device. The manner in which the coupling is reported by the CDC is not of importance. In some cases if maybe preferable to have the CDC configured to provide VSWR measurements. Of course, other indications of power coupling may be preferable. 
   Advantageously, the embodiments of the invention provide for a device that is manufactured in such a manner that power sensors are integrated therein without significantly increasing the size of the semiconductor die and its cost. 
   Numerous other embodiments may be envisaged without departing from the spirit or scope of the invention.