Variable gain amplifiers for communication systems
The present invention is directed to electrical circuits and techniques thereof. In various embodiments, the present invention provides a variable gain amplifier architecture that includes a continuous-time linear equalizer (CTLE) section and a variable gain amplifier (VGA) section. The CTLE section provides both a pair of equalized data signals and a common mode voltage. A DAC generates a control signal based on a control code. The VGA section amplifies the pair of equalized data signals by an amplification factor using a transistor whose resistance value is based on both the common mode voltage and the control signal. There are other embodiments as well.
1. A variable-gain amplifier device comprising:
an equalizer section comprising:
a first input switch coupled to a first input terminal, the first input switch comprising a first intermediate terminal;
a second input switch coupled to a second input terminal, the second input switch comprising a second intermediate terminal;
a first common resistor directly coupled to the first intermediate terminal;
a second common resistor directly coupled to the second intermediate terminal;
a common node directly coupled to the first common resistor and a second common resistor;
a digital-to-analog converter (DAC) including a control signal terminal coupled to the common node, the DAC being configured to generate a control signal based on a gain control code; and
an amplifier section comprising:
a third switch coupled to the first intermediate terminal;
a fourth switch coupled to the second intermediate terminal;
a transistor coupled to the third switch and the fourth switch, a resistance of the transistor being based on control signal.
2. The device of claim 1 wherein the transistor comprises a triode region transistor, a gate of the transistor being directly coupled to the control signal terminal.
3. The device of claim 2 further comprising a current source coupled to a source terminal of the transistor.
4. The device of claim 2 wherein the gain control code is stored in a lookup table.
5. The device of claim 1 further comprising:
a first load capacitor coupled to the first intermediate control terminal;
a second load capacitor coupled to the second intermediate control terminal.
6. The device of claim 1 wherein a sum of a common voltage and the control voltage is greater than a threshold voltage of the transistor.
7. The device of claim 1 wherein the gain control code is calibrated according to a voltage at the common node and a threshold voltage of the transistor.
8. The device of claim 6 wherein the threshold voltage is associated with a gate-source voltage differential.
9. The device of claim 1 wherein a gain control code is calibrated using a feedback mechanism.
10. The device of claim 1 further comprising a control module for generating the gain control code.
11. A variable gain amplifier device comprising:
a first transistor and a second transistor, the first transistor comprising a first gate terminal coupled to a first input signal and a first drain terminal coupled to a first output node, the second transistor comprising a second gate terminal coupled to a second input signal and a second drain terminal coupled to a second output node;
a first common mode resistor coupled to the first output node;
a second common mode resistor coupled to the second output node and the first common mode resistor;
a common node configured between the first common mode resistor and the second common mode resistor, the common node is characterized by a common mode voltage;
a digital-to-analog converter coupled to the common node;
a first switch coupled to the first output node;
a second switch coupled to the second output node; and
a transistor coupled to the third switch and the fourth switch, a resistance of the transistor being based on the common voltage.
12. The device of claim 11 wherein the first transistor comprises a PMOS transistor.
13. The device of claim 11 wherein the common node voltage is controlled by the digital-to-analog converter.
14. The device of claim 11 wherein the digital-to-analog converter is configured to generate a control voltage based on a code word.
15. The device of claim 14 wherein the common node voltage is greater than the control voltage.
16. A data communication system comprising:
a data communication interface for receiving a first input signal and a second input signal from a data transmission source via a communication channel, the data communication interface comprising a positive input resistor and a positive input coil, the data communication interface further comprising a negative input resistor and a negative input coil;
a continuous-time linear equalizer (CTLE) section configured for providing a common mode voltage and a first equalized signal and a second equalized signal based at least on the first input signal and the second input signal, the CTLE section comprising a pair of common mode resistors, the common mode voltage being configured between the pair of common mode resistors; and
a variable gain amplifier (VGA) section comprising a transistor and configured to generate a first amplified signal and a second amplified signal based on the first equalized signal and the second equalized signal, the VGA section being characterized by a gain ratio being at least based on a degeneration resistance value of the transistor, the degeneration resistance value being a function of the common mode voltage and a control signal.
17. The system of claim 16 further comprising a loss of signal detection module, wherein the clock data recovery module operates in a standby mode if the loss of signal detection module fails to detect signal presence.
18. The system of claim 16 wherein the data communication interface is coupled to a wired communication lane.
19. The system of claim 16 wherein the control signal is determined using a feedback mechanism.
20. The system of claim 16 wherein the control signal is determined using a lookup table.