Broadband cable modem amplifier with programmable bias current

A bias current-setting circuit for a programmable gain amplifier (PGA), the bias-current setting circuit comprising:

• a bandgap generator coupleable to a bias input of the PGA;
• an external resistor coupled to an input of the bandgap generator;
• a variable gain amplifier (VGA) having an input and an output, the VGA output coupled to a power amplifier stage bias input, the VGA input coupled to a bandgap generator output, the VGA adapted to provide bias current for the power amplifier stage, the bias current-setting circuit adapted to generate a nominal bias current;
• a digital-to-analog converter (DAC) having an input and an output adapted to receive a digital signal at the input and produce an analog signal at the output, the DAC output coupled to a bias input of the VGA;
• and
• a bias code generator coupled to the DAC input adapted to program the bias current of the power amplifier stage.

A cable modem for transmitting data signals between a cable modem termination system (CMTS) over a cable network, the cable modem comprising:

• a cable modem integrated circuit (IC) adapted to receive upstream data signals from a personal computing device, the cable modem IC having an output;
• a programmable gain amplifier (PGA) having an input and an output, the PGA input coupled to the cable modem IC output, the PGA having a programmable bias current and being adapted to amplify the upstream data signals;
• the PGA comprising:
• a power amplifier stage having an input, an output, and a bias input;
• and
• a bias current-setting circuit having coupled to the power amplifier stage bias input, wherein the power amplifier stage bias current is adapted to be programmed by the bias current-setting circuit;
• the PGA bias current-setting circuit comprising:
• a bandgap generator having an input and an output, the bandgap generator output coupled to the power amplifier stage bias input;
• an external bias resistor coupled to the input of the bandgap generator;
• a variable gain amplifier (VGA) having an input and an output, the VGA output coupled to the power amplifier stage input, the VGA input coupled to the bandgap generator, the VGA adapted to supply bias current for the power amplifier stage;
• a digital-to-analog converter (DAC) having an input and an output adapted to receive a digital signal at the input and produce an analog signal at the output, the DAC output coupled to a bias Input of the VGA;
• and
• a bias code generator coupled to the DAC input;
• and
• a tuner coupled to the PGA output adapted to modulate and demodulate the amplified upstream data signals in preparation for transmission to the CMTS.

A tuner adapted to modulate and demodulate data signals in preparation for transmission to a cable modem termination system (CMTS), the tuner comprising a programmable gain amplifier (PGA) for amplifying data signals before submission to the CMTS, the PGA comprising:

• a power amplifier stage having an input, an output, and a bias input;
• and
• a bias current-setting circuit, coupled to the power amplifier stage bias input, wherein the bias current-setting circuit is adapted to program a power amplifier stage bias current;
• the bias current-setting circuit comprising:
• a bandgap generator having an input and an output, the bandgap generator output coupled to the power amplifier stage bias input;
• an external bias resistor coupled to the input of the bandgap generator;
• a variable gain amplifier (VGA) having an input and an output, the VGA output coupled to the power amplifier stage input, the VGA input coupled to the bandgap generator output, the VGA adapted to supply bias current for the power amplifier stage;
• a digital-to-analog converter (DAC) having an input and an output adapted to receive a digital signal at the input and produce an analog signal at the output, the DAC output coupled to a bias input of the VGA;
• and
• a bias code generator coupled to the DAC input.