Amplitude-stabilized even order pre-distortion circuit
View Patent ↗An amplitude-stabilized second-order predistortion circuit includes a main cell having a differential input for receiving a differential input voltage, a differential output for providing a differential output voltage, and a load control input for receiving a load control voltage; a replica cell having a differential input for receiving a differential level of peak input voltage, a differential peak output voltage, and a load control input; and a control circuit coupled to the differential output of the replica cell and driving the load control inputs of the main cell and the replica cell. The main cell and the replica cell are multiplier cells each having a variable load. The control circuit includes a first amplifier for generating a single-ended peak signal and a second amplifier for generating the load control voltage from the difference between the replica cell single-ended peak output signal and a single-ended peak reference signal.
1. An amplitude-stabilized second order predistortion circuit comprising:
a main cell having a differential input for receiving a differential input voltage, a differential output for providing a differential output voltage, and a load control input for receiving a load control voltage;
a replica cell having a differential input for receiving a differential peak input voltage, a differential output, and a load control input; and
a control circuit coupled to the differential output of the replica cell and driving the load control inputs of the main cell and the replica cell,
wherein the main cell comprises a variable load.
2. The circuit of claim 1 wherein the replica cell comprises a variable load.
3. The circuit of claim 1 wherein the main cell comprises a multiplier cell.
4. The circuit of claim 1 wherein the replica cell comprises a multiplier cell.
5. The circuit of claim 1 wherein the control circuit comprises a first amplifier for generating a single-ended peak signal and a second amplifier for generating the load control voltage from the difference between the first single-ended peak signal and a single-ended reference signal.
6. The circuit of claim 1 wherein the control circuit comprises a differential amplifier.
7. The circuit of claim 1 wherein the control circuit comprises:
a first transistor having a control terminal, and coupled to a first current source at a first intermediate terminal;
a second transistor having a control terminal, and coupled to a second current source at a second intermediate terminal; and
a differential amplifier coupled to the first and second intermediate terminals for generating the load control voltage.
8. The circuit of claim 7 further comprising a sub-circuit interposed between the second transistor and the second current source to generate an adjustable voltage drop.
9. The circuit of claim 8 where the sub-circuit interposed between the second transistor and the second current source is a variable resistor device.
10. An amplitude-stabilized second order predistortion circuit comprising:
a first second-order predistortion circuit having an input for receiving an input signal, an output for providing a correction output signal, and a variable load;
a second second-order predistortion circuit having an input for receiving a peak input signal, an output for providing a correction peak output signal, and a variable load; and
a gain and loop stabilization circuit having a first input for receiving the correction peak output signal, a second input for receiving a correction amplitude set point, and an output coupled to the variable load of the first and second second-order predistortion circuits.
11. The circuit of claim 10 wherein the variable load of the first and second-order predistortion circuits comprises an active load.
12. The circuit of claim 10 wherein the first second-order predistortion circuit comprises a multiplier cell.
13. The circuit of claim 10 wherein the second second-order predistortion circuit comprises a multiplier cell.
14. The circuit of claim 10 wherein the gain and loop stabilization circuit comprises a differential amplifier.
15. An amplitude-stabilized even order predistortion circuit comprising:
a first even-order predistortion circuit having an input for receiving an input signal, an output for providing a correction output signal, and a variable load;
a second even-order predistortion circuit having an input for receiving a peak input signal, an output for providing a correction peak output signal, and a variable load; and
a gain and loop stabilization circuit having a first input for receiving the correction peak output signal, a second input for receiving a correction amplitude set point, and an output coupled to the variable load of the first and second even-order predistortion circuits.
16. The circuit of claim 15 wherein the variable load of the first and second even-order predistortion circuits comprises an active load.
17. The circuit of claim 15 wherein the first even-order predistortion circuit and the second even-order predistortion circuit comprise a cascade of a plurality of multiplier cells.
18. The circuit of claim 15 wherein the first even-order predistortion circuit and the second even-order predistortion circuit comprise a plurality of multiplier cell coupled according to a binary tree topology.
19. The circuit of claim 15 wherein the gain and loop stabilization circuit comprises a differential amplifier.