Gain adjustment for programmable gain amplifiers

A programmable gain amplifier circuit for receiving an input signal and providing an output signal with an adjustable gain corresponding to a user initiated gain setting, the programmable gain amplifier circuit comprising:

• an operation amplifier circuit including a non-inverting input terminal configured to receive the input signal, an inverting input terminal configured to receive a feedback signal, and an output terminal configured to provide the output signal;
• a digitally controlled potentiometer means that is coupled between the output terminal and a reference terminal, wherein the digitally controlled potentiometer means includes a wiper terminal that is coupled to the inverting input terminal, wherein the digitally controlled potentiometer has a first resistance value between the output terminal and an intermediate node, a second resistance value between the intermediate node and the wiper terminal, and a third resistance value between the wiper terminal and the reference terminal, wherein the second and third resistance values vary in response to a gain select control signal by adjusting a wiper setting for the digitally controlled potentiometer means;
• a first capacitor means that is coupled between the reference terminal and the intermediate node;
• a second capacitor means that is coupled between the output terminal and the intermediate node;
• a first resistor means;
• a switching means that includes a first switching terminal coupled to the intermediate node through the first resistor means, a second switching terminal coupled to the reference terminal, and a third switching terminal coupled to the output terminal, wherein the switching means is arranged to couple the first switching terminal to the reference terminal in a first position, wherein the switching means is also arranged to coupled to the first switching terminal to the output terminal in a second position, and wherein the switching means selects one of the first position and the second position in response to a gain trim control signal;
• and
• a control means that is arranged to provide the gain control signal and the gain trim control signal in response to the user initiated gain setting, wherein the gain trim control signal is modulated such that the switching means oscillates between the first position and the second position according to a duty cycle assigned to the user initiated gain setting, wherein the duty cycle corresponds to the time averaged modulation between the first position and the second position.

A method for trimming gain adjustments in a programmable gain amplifier circuit that receives an input signal and provides an output signal in response thereto, wherein the programmable gain amplifier has an adjustable gain corresponding to a user initiated gain setting, the method comprising:

• retrieving a duty cycle setting for a switching circuit from a look-up-table in response to the user initiated gain setting;
• adjusting a gain setting control signal for a digitally controlled potentiometer in response to the user initiated gain setting, wherein the digitally controlled potentiometer is coupled between an output terminal of an operational amplifier circuit and a reference terminal, wherein the digitally controlled potentiometer includes a wiper terminal that is coupled to an inverting input terminal of the operational amplifier circuit, wherein the digitally controlled potentiometer has a first resistance value between the output terminal and an intermediate node, a second resistance value between the intermediate node and the wiper terminal, and a third resistance value between the wiper terminal and the reference terminal, wherein the second and third resistance values vary in response to a gain select control signal by adjusting a wiper setting for the digitally controlled potentiometer;
• coupling a first capacitor between the intermediate node and the inverting input terminal;
• coupling a second capacitor between the intermediate node and the output terminal;
• selectively coupling the output terminal to the intermediate node through a resistor when a switching means is in a first position in response to a gain trim control signal;
• selectively coupling the reference terminal to the intermediate node through the resistor when the switching means is in a second position in response to the gain trim control signal;
• and
• dynamically adjusting the gain trim control signal such that the switching means modulates between the first position and the second position according to the retrieved duty cycle for the user initiated gain setting, wherein the duty cycle corresponds to the time averaged modulation between the first position and the second position.