Differential output circuits with configurable harmonic reduction circuits and methods of operation thereof

A transmitter comprising:

• an amplifier with a differential output, wherein the differential output includes first and second differential output terminals, and wherein the amplifier is configured to amplify an input signal and to produce a differential output signal at the differential output during operation of the amplifier;
• a balun with a primary winding and a secondary winding, wherein the primary winding has a first balun terminal coupled to the first differential output terminal, and a second balun terminal coupled to the second differential output terminal;
• a configurable harmonic reduction circuit that includes
• a first configurable shunt capacitance circuit coupled between the first differential output terminal and a ground reference node, and
• a second configurable shunt capacitance circuit coupled between the second differential output terminal and the ground reference node;
• a control circuit configured to receive tuning data associated with a calibrated tuning state, wherein the tuning data indicates a first calibrated capacitance value for the first configurable shunt capacitance circuit and a second calibrated capacitance value for the second configurable shunt capacitance circuit, and wherein the control circuit is further configured to control the first configurable shunt capacitance circuit to have the first calibrated capacitance value, and to control the second configurable shunt capacitance circuit to have the second calibrated capacitance value;
• and
• a calibration circuit coupled to the differential output, wherein the calibration circuit is configured to
• generate a duty cycle measurement of the differential output signal for a plurality of tuning states, and
• identify the calibrated tuning state as one of the plurality of tuning states for which the duty cycle measurement is closest to 50 percent.

A transmitter comprising:

• an amplifier with a differential output, wherein the differential output includes first and second differential output terminals, and wherein the amplifier is configured to amplify an input signal and to produce a differential output signal at the differential output during operation of the amplifier;
• a balun with a primary winding and a secondary winding, wherein the primary winding has a first balun terminal coupled to the first differential output terminal, and a second balun terminal coupled to the second differential output terminal;
• a configurable harmonic reduction circuit that includes
• a first configurable shunt capacitance circuit coupled between the first differential output terminal and a ground reference node, and
• a second configurable shunt capacitance circuit coupled between the second differential output terminal and the ground reference node;
• and
• a control circuit configured to receive tuning data associated with a calibrated tuning state, wherein the tuning data indicates a first calibrated capacitance value for the first configurable shunt capacitance circuit and a second calibrated capacitance value for the second configurable shunt capacitance circuit, and wherein the control circuit is further configured to control the first configurable shunt capacitance circuit to have the first calibrated capacitance value, and to control the second configurable shunt capacitance circuit to have the second calibrated capacitance value, and
• wherein the first configurable shunt capacitance circuit includes a first input coupled to the first differential output terminal, and a number, N, of first capacitance legs coupled between the first input and the ground reference node, wherein each of the first capacitance legs includes a capacitor coupled in series with a switching element, and wherein the control circuit is configured to control the first configurable shunt capacitance circuit to have the first calibrated capacitance value by controlling the switching element in each of the first capacitance legs to connect or disconnect, from the first configurable shunt capacitance circuit, the capacitor in each of the first capacitance legs, and
• the second configurable shunt capacitance circuit includes a second input coupled to the second differential output terminal, and the number, N, of second capacitance legs coupled between the second input and the ground reference node, wherein each of the second capacitance legs includes a capacitor coupled in series with a switching element, and wherein the control circuit is configured to control the second configurable shunt capacitance circuit to have the second calibrated capacitance value by controlling the switching element in each of the second capacitance legs to connect or disconnect, from the second configurable shunt capacitance circuit, the capacitor in each of the second capacitance legs.

An electronic circuit comprising:

• a differential output circuit that includes a differential output, wherein the differential output includes first and second differential output terminals, and wherein the differential output circuit is configured to produce a differential output signal at the differential output during operation of the electronic circuit;
• a balun with a primary winding and a secondary winding, wherein the primary winding has a first balun terminal coupled to the first differential output terminal, and a second balun terminal coupled to the second differential output terminal;
• a configurable harmonic reduction circuit that includes
• a first configurable shunt capacitance circuit coupled between the first differential output terminal and a ground reference node, and
• a second configurable shunt capacitance circuit coupled between the second differential output terminal and the ground reference node;
• memory configured to store, for each of a plurality of tuning states, tuning data indicating a combination of first and second capacitance values for the first and second configurable shunt capacitance circuits, respectively, wherein the combination of capacitance values for at least some of the plurality of tuning states indicates that the first and second capacitance values are different from each other;
• and
• a control circuit configured to receive, from the memory, the tuning data associated with a calibrated tuning state selected from the plurality of tuning states, wherein the tuning data indicates a first calibrated capacitance value for the first configurable shunt capacitance circuit and a second calibrated capacitance value for the second configurable shunt capacitance circuit, and wherein the control circuit is further configured to control the first configurable shunt capacitance circuit to have the first calibrated capacitance value, and to control the second configurable shunt capacitance circuit to have the second calibrated capacitance value.

A method of operating an electronic circuit that includes a differential output circuit with a differential output, and a balun with a primary coil coupled across the differential output, the method comprising:

• storing, in a memory, tuning data for each of a plurality of tuning states, wherein the tuning data indicates a combination of first and second capacitance values for first and second configurable shunt capacitance circuits, respectively, and wherein the combination of capacitance values for at least some of the plurality of tuning states indicates that the first and second capacitance values are different from each other;
• receiving, by a control circuit from the memory, the tuning data associated with a calibrated tuning state selected from the plurality of tuning states, wherein the tuning data indicates a first calibrated capacitance value for the first configurable shunt capacitance circuit and a second calibrated capacitance value for the second configurable shunt capacitance circuit, wherein the first configurable shunt capacitance circuit is coupled to a first differential output terminal of the differential output, and the second configurable shunt capacitance circuit is coupled to a second differential output terminal of the differential output;
• controlling, by the control circuit, the first configurable shunt capacitance circuit to have the first calibrated capacitance value;
• controlling, by the control circuit, the second configurable shunt capacitance circuit to have the second calibrated capacitance value;
• providing an input signal to the differential output circuit, resulting in generation of a differential output signal at the differential output;
• and
• conveying the differential output signal to the primary coil of the balun.