System and method for linearization of a mixer
View Patent ↗A mixer may include a linearization circuit. The linearization circuit may include and operation amplifier, a first pass device, a second pass device, a first feedback resistor, and a second feedback resistor. Each of the first pass device and the second pass device may have a gate terminal, a first non-gate terminal, and a second non-gate terminal and coupled to its gate terminal to an output terminal of the operational amplifier and configured to be coupled at its first non-gate terminal to a high potential source. Each of the first feedback resistor and the second feedback resistor may have a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal coupled to the second non-gate terminal of an associated pass device and the positive polarity of the differential baseband output.
1. A mixer, comprising:
a Gilbert cell comprising:
a transconductance stage having a differential baseband input and differential baseband output, the differential baseband output having a positive polarity and a negative polarity; and
a mixer stage configured to modulate a signal present at the differential baseband output;
a linearization circuit comprising:
an operational amplifier having an output terminal, a positive input terminal, and a negative input terminal, and configured to receive a common-mode bias voltage at the negative input terminal;
a first pass device having a gate terminal, a first non-gate terminal, and a second non-gate terminal and coupled to its gate terminal to the output terminal of the operational amplifier and configured to be coupled at its first non-gate terminal to a high potential source;
a second pass device having a gate terminal, a first non-gate terminal, and a second non-gate terminal and coupled to its gate terminal to the output terminal of the operational amplifier and configured to be coupled at its first non-gate terminal to the high potential source;
a first feedback resistor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal coupled to the second non-gate terminal of the first pass device and the positive polarity of the differential baseband output; and
a second feedback resistor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal coupled to the second non-gate terminal of the second pass device and the negative polarity of the differential baseband output.
2. The mixer of claim 1 , wherein any of the first pass device and the second pass device comprises a transistor.
3. The mixer of claim 1 , wherein any of the first pass device and the second pass device comprises a p-type metal-oxide-silicon field-effect transistor.
4. The mixer of claim 1 , wherein the first resistor and the second resistor have approximately the same resistance.
5. The mixer of claim 1 , the linearization circuit further comprising a capacitor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal configured to be coupled to a low-potential source.
6. The mixer of claim 5 , wherein a capacitance of the capacitor and a resistance of at least one of the first resistor and the second resistor are selected to set a bandwidth for a common-mode feedback loop formed by the linearization circuit.
7. The mixer of claim 1 , the Gilbert cell further comprising an output stage comprising a cascoded common-gate current buffer.
8. The mixer of claim 1 , the Gilbert cell further comprising an output stage comprising an output balun and at least one tuning capacitor for tuning the output stage.
9. A wireless communication element, comprising:
a transmit path configured to convert a first digital signal into a first modulated wireless communication signal and transmit the first modulated wireless communication signal; and
a receive path configured to receive a second modulated wireless communication signal and convert the second wireless communication signal into a second digital signal;
wherein at least one of the transmit path and the receive path comprises a mixer comprising:
a Gilbert cell comprising:
a transconductance stage having a differential baseband input and differential baseband output, the differential baseband output having a positive polarity and a negative polarity; and
a mixer stage configured to modulate a signal present at the differential baseband output;
a linearization circuit comprising:
an operational amplifier having an output terminal, a positive input terminal, and a negative input terminal, and configured to receive a common-mode bias voltage at the negative input terminal;
a first pass device having a gate terminal, a first non-gate terminal, and a second non-gate terminal and coupled to its gate terminal to the output terminal of the operational amplifier and configured to be coupled at its first non-gate terminal to a high potential source;
a second pass device having a gate terminal, a first non-gate terminal, and a second non-gate terminal and coupled to its gate terminal to the output terminal of the operational amplifier and configured to be coupled at its first non-gate terminal to the high potential source;
a first feedback resistor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal coupled to the second non-gate terminal of the first pass device and the positive polarity of the differential baseband output; and
a second feedback resistor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal coupled to the second non-gate terminal of the second pass device and the negative polarity of the differential baseband output.
10. The wireless communication element of claim 9 , wherein any of the first pass device and the second pass device comprises a transistor.
11. The wireless communication element of claim 9 , wherein any of the first pass device and the second pass device comprises a p-type metal-oxide-silicon field-effect transistor.
12. The wireless communication element of claim 9 , wherein the first resistor and the second resistor have approximately the same resistance.
13. The wireless communication element of claim 9 , the linearization circuit further comprising a capacitor having a first terminal and a second terminal, the first terminal coupled to the positive input terminal of the operational amplifier and the second terminal configured to be coupled to a low-potential source.
14. The wireless communication element of claim 13 , wherein a capacitance of the capacitor and a resistance of at least one of the first resistor and the second resistor are selected to set a bandwidth for a common-mode feedback loop formed by the linearization circuit.
15. The wireless communication element of claim 9 , the Gilbert cell further comprising an output stage comprising a cascoded common-gate current buffer.
16. The wireless communication element of claim 9 , the Gilbert cell further comprising an output stage comprising an output balun and at least one tuning capacitor for tuning the output stage.