Programmable gain trim circuit

A programmable gain amplifier circuit comprising:

• a differential amplifier that includes an inverting input terminal, a non-inverting input terminal, and an output terminal, wherein the inverting input terminal is coupled to a feedback node, the non-inverting input is arranged to receive an input signal, and wherein the output terminal is coupled to an output node;
• a first gain setting feedback circuit that includes a first terminal that is coupled to a the output node, a second terminal that is coupled to a first intermediate node, and a third terminal that is coupled to a circuit ground, wherein the first gain setting feedback circuit has an associated first gain value (G1), wherein the first gain setting feedback circuit comprises:
• a first resistor circuit (RF1) that is coupled between the output node and the first intermediate node, and a second resistor circuit (RA1) that is coupled between the first intermediate node and the circuit ground;
• a second gain setting feedback circuit that includes a first terminal that is coupled to the output node, a second terminal that is coupled to a second intermediate node, and a third terminal that is coupled to the circuit ground, wherein the second gain setting feedback circuit has an associated second gain value (G2) that is different from the first gain value (G1), and wherein the second gain setting feedback circuit comprises:
• a third resistor circuit (RF2) that is coupled between the output node and the second intermediate node and a fourth resistor circuit (RA2) that is coupled between the second intermediate node and the circuit ground;
• a trim adjustment circuit that includes a first terminal that is coupled to the first intermediate node, a second terminal that is coupled to the second intermediate node, and a third terminal that is coupled to the feedback node, wherein the trim adjustment circuit is arranged to adjust a gain trim associated with the programmable gain amplifier in response to a digital control signal (DCTL) such that a gain factor associated with the programmable gain amplifier is a blend of the first gain value (G1) and the second gain value (G2);
• and
• a gain skewing resistor circuit that is arranged in parallel with one of the first resistor circuit (RF1), the second resistor circuit (RA1), the third resistor circuit (RF2), and the fourth resistor circuit (RA2).

A method for adjusting gains in a programmable gain amplifier, comprising:

• selecting a first gain setting for the programmable gain amplifier from a first set of gain settings such that a first gain corresponds to G1=[1+(RF1/RA1)];
• selecting a second gain setting for the programmable gain amplifier from a second set of gain settings such that a second gain setting corresponds to G2=[1+(RF2/RA2)];
• cycling through each available trim setting for the selected first gain setting and the selected second gain setting by adjusting a blending factor between the first gain setting (G1) and the second gain setting (G2) in response to the trim setting such that the overall gain (G) is given by:
• G=G1*a+G2*b, where a+b=1, and wherein the value of a and b are determined by the blending factor;
• determining a non-ideal gain factor associated with each available trim setting;
• comparing the non-ideal gain factors to an ideal gain factor associated with selected gain setting;
• selecting an appropriate trim setting from the available trim settings based on the comparison;
• storing the value associated with the trim setting in a trim map;
• and
• indexing the stored value in the trim map according to the selected gain setting.

A method for adjusting a gain in a programmable gain amplifier, comprising:

• identifying a gain change in the programmable gain amplifier;
• adjusting a first gain setting in response to the identified gain change, wherein the first gain setting is associated with a first gain setting feedback circuit that has a first gain setting given by G1=[1+(RF1/RA1)];
• adjusting a second gain setting in response to the identified gain change, wherein the second gain setting is associated with a first gain setting feedback circuit that has a second gain setting given by G2=[1+(RF2/RA2)];
• retrieving a trim setting from a trim map in response to the identified gain change;
• and
• adjusting a blending factor between the first gain setting (G1) and the second gain setting (G2) in response to the identified gain change such that the overall gain (G) is given by:
• G=G1*a+G2*b, where a+b=1, and wherein the value of a and b are determined by the blending factor.

An apparatus for adjusting a gain in a programmable gain amplifier, comprising:

• a means for selected a first gain (G1) in a first gain feedback circuit in response to a gain setting such that G1=[1+(RF1/RA1)];
• a means for selecting a second gain (G2) in a second gain feedback circuit in response to the gain setting such that G2=[1+(RF2/RA2)];
• a means for identifying a predetermined trim setting in response to the gain setting;
• and
• a means for adjusting a blending factor between the first gain and the second gain in response to at least one of the gain setting and the trim setting such that the overall gain (G) is given by:
• G=G1*a+G2*b, where a+b=1, and wherein the value of a and b are determined by the blending factor.