Gain boosting for tuned differential LC circuits
A gain boost circuit and methodology are described for providing improved gain boosting with tuned amplifier circuits, such as differential low noise amplifier circuits having output resonant tank circuits. By selectively controlling the current source for a negative transconductance stage coupled between the differential amplifier output and the output resonant tank circuits, the amplifier gain may be adjusted to compensate for temperature variations. In addition, the amplifier gain boost may be selectively added, removed or even incrementally adjusted by using a current source control circuit in the negative transconductance stage to adjust the negative transconductance value generated by the negative transconductance stage.
1. A gain boost amplifier circuit, comprising:
a signal amplifier circuit for amplifying an input signal by a gain value to generate an amplified signal at an output;
an output resonant circuit coupled to the output that is tuned to provide a first impedance level for the signal amplifier circuit; and
an adjustable negative transconductance stage coupled between the output resonant circuit and the signal amplifier circuit for generating an adjustable negative transconductance value, thereby boosting the gain value of the signal amplifier circuit.
2. The gain boost amplifier circuit of claim 1 , wherein the adjustable negative transconductance stage comprises:
a current source transistor;
a current source control circuit coupled to the current source transistor; and
a pair of cross-coupled transistors coupled between the current source transistor and the output of the signal amplifier circuit, where the current source control circuit controls the current through the current source transistor to adjust the adjustable negative transconductance value.
3. The gain boost amplifier circuit of claim 2 , where the current source control circuit comprises a current source coupled through a power down circuit and diode-connected transistor to the current source transistor, whereby the power down circuit is used to control the adjustable negative transconductance stage.
4. The gain boost amplifier circuit of claim 3 , where the power down circuit comprises at least one switch control transistor coupled between the current source and the diode-connected transistor.
5. The gain boost amplifier circuit of claim 2 , where the current source control circuit comprises a PTAT current source for controlling the current through the current source transistor to reduce the adjustable negative transconductance value as the temperature increases.
6. The gain boost amplifier circuit of claim 5 , where the current source control circuit comprises a power down circuit coupled to the PTAT current source.
7. The gain boost amplifier circuit of claim 2 , where the current source control circuit comprises a digitally controlled current source coupled through a diode-connected transistor to the current source transistor, whereby the digitally controlled current source controls the current through the current source transistor to provide different current levels for the adjustable negative transconductance stage.
8. The gain boost amplifier circuit of claim 7 , where the current source control circuit comprises a power down circuit coupled between the digitally controlled current source and the diode-connected transistor.
9. The gain boost amplifier circuit of claim 8 , wherein the power down circuit comprises a pair of switch control transistors coupled between the digitally controlled current source and the diode-connected transistor.
10. The gain boost amplifier circuit of claim 1 implemented as a low noise amplifier in a receiver.
11. A method for boosting a gain level for a signal amplifier, comprising selectively coupling an adjustable negative transconductance circuit between an amplifier circuit and an output tank circuit to selectively generate an adjustable negative transconductance value to compensate for any losses generated by the output tank circuit.
12. The method of claim 11 , where the adjustable negative transconductance circuit comprises:
a current source transistor;
a current source control circuit coupled to the current source transistor; and
a pair of cross-coupled transistors coupled between the current source transistor and the signal amplifier, where the current source control circuit controls the current through the current source transistor to adjust the adjustable negative transconductance value.
13. The method of claim 11 , where selectively coupling the adjustable negative transconductance circuit comprises turning the adjustable negative transconductance circuit off in response to a power down signal and turning the adjustable negative transconductance circuit on in response to a power up signal.
14. The method of claim 11 , where selectively coupling the adjustable negative transconductance circuit comprises applying a PTAT current source to the adjustable negative transconductance circuit to increase the amount of current supplied to the adjustable negative transconductance circuit in response to temperature changes.
15. The method of claim 11 , where the selectively coupling the adjustable negative transconductance circuit comprises applying a digitally controlled current source to the adjustable negative transconductance circuit to provide different current levels to the adjustable negative transconductance circuit.
16. A receiver comprising:
an amplifier circuit coupled to receive and amplify a signal by a gain factor,
an output tank circuit coupled to the amplifier circuit and tuned to increase the gain of the amplifier circuit, and
an adjustable negative transconductance circuit selectively coupled to the output tank circuit.
17. The receiver of claim 16 , further comprising a temperature controlled current source for controlling the amount of current provided to the negative transconductance circuit in response to temperature.
18. The receiver of claim 16 , further comprising a switchable current source circuit for providing a plurality of different current levels to the negative transconductance circuit.
19. The receiver of claim 16 , where the amplifier circuit comprises a differential low noise amplifier circuit in an integrated circuit receiver front end.
20. The receiver of claim 16 , further comprising a connection circuit for selectively coupling the adjustable negative transconductance circuit to the output tank circuit in response to a power up signal.