Power amplifier having a nonlinear output capacitance equalization
Power amplifier (PA), regardless of the process used for the manufacturing of its devices, suffers from a nonlinear output capacitance that has significant impact on various aspects of the PA performance. This output capacitance is dependent on the large output voltage swing. Accordingly a compensation capacitance is added at the output of the PA that has a behavior that is inverse respective of the output voltage of that of the output capacitance of the PA. Connecting the compensation capacitor in parallel to the PA output capacitance, results in a total capacitance that is the sum of the output capacitance and its compensation capacitance. The total output capacitance is therefore essentially stable throughout the output voltage swing.
1. A power amplifier (PA) system comprising:
a signal path comprising a plurality of gain stages;
an output stage the input of which is coupled to the output of the last gain stage of the signal path, the output stage having a nonlinear output capacitance; and
a capacitance equalization block connected to the output of the output stage that at least approximately compensates for the nonlinearity of the output stage output capacitance;
such that the total output capacitance of the PA is essentially constant.
2. The PA system of claim 1 , further comprising:
a capacitance equalization block connected to at least the last gain stage of the signal path.
3. The PA system of claim 1 , wherein the capacitance equalization block comprises at least one of: a nonlinear analog capacitance, a nonlinear mixed signal capacitance, a nonlinear digital capacitance.
4. The PA system of claim 3 , wherein the nonlinear analog capacitance comprises at least one of: diode junction capacitance, MOS inversion capacitance, MOS accumulation capacitance.
5. The PA system of claim 3 , wherein the nonlinear mixed-signal capacitance comprises at least one of: a sharply switched capacitance, a continuously switched capacitance.
6. The PA system of claim 3 , wherein the nonlinear digital capacitance comprises at least one of: switched capacitor, capacitive digital-to-analog convertor (DAC).
7. The PA system of claim 6 , wherein the capacitor DAC is used to implement a piecewise linear approximation of a nonlinear capacitance.
8. The PA system of claim 1 , wherein the capacitance equalization block is controlled by at least one of: an output voltage from the output stage, an input voltage to the output stage, an impedance of a load connected to the output stage, temperature, supply voltage, process corner, a detector.
9. The PA system of claim 1 , further comprising:
a voltage standing-wave ratio (VSWR) detector that controls the capacitance equalization block respective of detection of a load connected to the output of the PA system.
10. The PA system of claim 1 wherein the signal path is a radio frequency signal path.