Distributed quality factor adjustment
View Patent ↗A system includes a differential circuit, multiple cross-coupled transconductance circuits. In some implementations, the differential circuit may include an inductor coil in a balun or transformer. The cross-coupled transconductance circuits may act to reduce the internal resistance of the differential circuit to increase the quality factor of the differential circuit. The cross-coupled transconductance circuit may be connected at differential points along the differential circuit and be engaged and disengaged to linearize the quality factor of the differential circuit.
1. A device, comprising:
a differential circuit comprising:
a first pair of ports, the first pair of ports characterized by a first resistance; and
a second pair of ports, the second pair of ports characterized by a second resistance;
a first transconductance circuit (TC) coupled across the first pair of ports, the first TC configured to, when engaged, reduce the first resistance; and
a second TC coupled across the second pair of ports, the second TC configured to, when engaged, reduce the second resistance;
control circuitry configured to:
detect a signal incident on the differential circuit;
determine when the signal crosses a threshold; and
responsive to the signal crossing the threshold:
engage the first TC; and
disengage the second TC.
2. The device of claim 1 , where the first TC comprises a first path from a virtual ground to a first port of the first pair of ports, the first path comprising a first transistor.
3. The device of claim 2 , where the first path further comprises a second path from the virtual ground to a second port of the first pair of ports, the second path comprising a second transistor, the second port coupled to a first gate of the first transistor, the first port coupled to a second gate of the second transistor.
4. The device of claim 3 , where the first port is configured to drive, responsive to a signal at the first port, a response at the second port via the second gate of the second transistor.
5. The device of claim 1 , where a first signal at a first port of the first pair of ports is configured to receive an inverted signal with respect to a second signal at a second port of the first pair of ports.
6. The device of claim 1 , where the first pair of ports comprises a differential input port for the differential circuit.
7. The device of claim 1 , where the differential circuit comprises a differential inductor comprising a differential input port.
8. The device of claim 7 , where the differential inductor comprises:
a first coil of a balun; and
a second coil of the balun, inter-wound with the first coil.
9. The device of claim 8 , where the balun is configured to convert a differential input signal at the differential input port to a single-ended signal at the second coil.
10. A method, comprising:
detecting a voltage swing incident on a differential circuit, the differential circuit comprising a first pair of ports and a second pair of ports;
determining when the voltage swing has crossed a signal level threshold, and in response:
increasing an impedance across the first pair of ports by disengaging a first cross-coupled transconductance circuit (CCTC) across the first pair of ports; and
decreasing an impedance across the second pair of ports by engaging a second CCTC across the second pair of ports.
11. The method of claim 10 , where determining when the voltage swing has crossed a signal level threshold comprises determining that an amplitude of the voltage swing increased to a value above the signal level threshold.
12. The method of claim 10 , where determining when the voltage swing has crossed a signal level threshold comprises determining that an amplitude of the voltage swing decreased to a value below the signal level threshold.
13. The method of claim 10 , where engaging the second CCTC comprises engaging a finger transistor element within the CCTC.
14. The method of claim 10 , where disengaging the first CCTC comprises opening a switch along path between a virtual ground and a transistor of the first CCTC.
15. The method of claim 10 , where determining when the voltage swing has crossed a signal level threshold comprises:
receiving an indication of an amplification level of an amplifier producing the voltage swing; and
determining when the amplification level has crossed an amplification level threshold.
16. A device, comprising:
a differential inductor comprising:
a coil wound between a pair of differential ports configured to receive a differential signal;
a first virtual ground port connected to the coil at a point between the pair of differential ports;
a first pair of connection ports connected to the coil, the first pair of connections ports comprising a first resistance and first pair of connection ports configured to receive a first voltage swing responsive to the differential signal; and
a second pair of connection ports, between the first pair connection ports and the first virtual ground port, the second pair of connection ports comprising a second resistance and second pair of connection ports configured to receive a second voltage swing that is smaller than the first voltage swing;
a first cross-coupled transconductance circuit (CCTC) connected across the first pair of connection ports, the first CCTC configured to, when engaged, reduce the first resistance; and
a second CCTC connected across the second pair of connection ports, the second CCTC configured to, when engaged, reduce the second resistance;
circuitry, coupled to the first and second CCTCs, configured to:
determine if the differential signal has exceeded a signal level threshold;
responsive to the differential signal exceeding the signal level threshold, disengage the first CCTC; and
responsive to the differential signal exceeding the signal level threshold, engage the second CCTC.
17. The device of claim 16 , where the first CCTC comprises:
a first path from a second virtual ground port to a first connection port of the first pair of connection ports, the first path comprising a first transistor; and
a second path from the second virtual ground port to a second connection port of the first pair of connection ports, the second path comprising a second transistor, the second connection port coupled to a first gate of the first transistor, the first connection port coupled to a second gate of the second transistor.
18. The device of claim 17 , where a first switch is coupled along the first and second paths between the second virtual ground port and the first and second transistors; and
where the circuitry is further configured to disengage the first CCTC via operation of the first switch.
19. The device of claim 16 , where the first CCTC is configured to, when engaged, generate a nonlinear response to voltage swings across the first pair of connection ports corresponding to differential signals that exceed the signal level threshold.
20. The device of claim 19 , where the circuitry is configured to adjust a quality factor of the differential inductor by disengaging the first CCTC and engaging the second CCTC when the differential signal exceeds the signal level threshold.