Digitally-controlled transimpedance amplifier (tia) circuit and methods

A digitally-controlled transimpedance amplifier (TIA) circuit comprising:

• a first TIA having a first input terminal and a first output terminal;
• a first variable impedance having first and second terminals electrically coupled to the first input and first output terminals, respectively;
• at least a first variable gain amplifier (VGA) circuit having a second input terminal and a second output terminal, the second input terminal being electrically coupled to the first output terminal, the VGA circuit having N variable gain stages where N is a positive integer;
• an output driver circuit having a third input terminal and a third output terminal, the third input terminal being electrically coupled to the second output terminal;
• and
• digital loop-control circuitry comprising analog-to-digital conversion (ADC) circuitry, digital controller circuitry and digital-to-analog conversion (DAC) circuitry, the ADC circuitry being electrically coupled to the first, second and third output terminals and to an output terminal of a received signal strength indicator (RSSI) circuit that measures a signal strength of an electrical analog signal produced by a photodetector that is electrically coupled to the first input terminal of the first TIA and outputs an RSSI output signal from an RSSI output terminal of the RSSI circuit, the ADC circuitry converting first, second, third output signals and the RSSI output signals out from said first, second, third output terminals and from the RSSI output terminal into at least first, second, third and fourth digital signals, the digital controller circuitry processing the first, second, third and fourth digital signals and producing P digital control signals, where P is equal to at least N+2, the DAC converting the P digital control signals into P analog control signals, respectively, and wherein P−2 of the analog control signals are fed back to the VGA circuit and used to vary gains of one or more of the N variable gain stages, respectively, and wherein one of the P analog control signals is fed back to direct current (DC) offset cancellation circuitry for use as a DC offset cancellation value by the DC offset cancellation circuitry, and wherein one of the P−2 analog control signals is fed back to the TIA and used to vary an impedance of the first variable impedance.

A method of performing digital feedback loop control in a transimpedance amplifier (TIA) circuit, the method comprising:

• in digital loop-control circuitry, receiving first, second, third and fourth output signals from a first TIA, a first variable gain amplifier (VGA) circuit, an output driver circuit, and a received signal strength indicator (RSSI) circuit, respectively, the first TIA having a first input terminal and a first output terminal, wherein a variable impedance is electrically coupled to the TIA in a feedback loop interposed between the first input terminal and the first output terminal, the VGA circuit having a second input terminal and a second output terminal, the second input terminal being electrically coupled to the first output terminal, the VGA circuit having N variable gain stages where N is a positive integer, the output driver circuit having a third input terminal and a third output terminal, the third input terminal being electrically coupled to the second output terminal;
• with analog-to-digital conversion (ADC) circuitry of the digital loop-control circuitry electrically coupled to the first, second and third output terminals and to an output terminal of a received signal strength indicator (RSSI) circuit that measures a signal strength of an electrical analog signal produced by a photodetector, receiving first, second, third and fourth signals output from the TIA, the VGA circuit, the output driver circuit and the RSSI circuit, respectively, and converting the first, second, third and fourth output signals into at least first, second, third and fourth digital signals;
• in a digital controller of the digital loop-control circuitry, processing the first, second, third and fourth digital signals and producing P digital control signals, where P is equal to at least N+2;
• with a digital-to-analog converter (DAC) of the digital loop-control circuitry, converting the P digital control signals into P analog control signals, respectively;
• and
• with the digital loop control circuitry, feeding P−2 of the analog control signals back to the VGA circuit for use in varying a gain of one or more of the N variable gain stages, respectively, feeding one of the P analog control signals back to direct current (DC) offset cancellation circuitry for use as a DC offset cancellation value by the DC offset cancellation circuitry, and feeding one of the P−2 analog control signals back to the TIA for use in varying the variable impedance.