Transmitter digital-to-analog converter (DAC)-baseband filter (BBF) common mode interface

A method for removing common-mode current from a pair of complementary current signals from a DAC in a transmitter, the method comprising:

• generating a common-mode voltage of the pair of complementary current signals comprising at least a first current signal and a second current signal output from the DAC of the transmitter;
• measuring and outputting a difference voltage between the generated common-mode voltage and a common-mode reference voltage;
• and
• removing at least a portion of the common-mode current from the first current signal and the second current signal directly from an output of DAC based on the difference voltage.

An apparatus for a transmitter for removing common-mode current from a pair of complementary current signals from a DAC, the apparatus comprising:

• means for generating a common-mode voltage of the pair of complementary current signals comprising at least a first current signal and a second current signal output from the DAC of the transmitter;
• means for measuring and outputting a difference voltage between the generated common-mode voltage and a common-mode reference voltage;
• and
• means for removing the common-mode current from the first current signal and the second current signal directly from an output of the DAC based on the difference voltage.

An interface circuit of a transmitter for removing common-mode current from a pair of complementary current signals received from a digital-to-analog converter (DAC) and sent to a baseband filter (BBF) of a transmitter, the circuit comprising:

• a first node configured to receive a first current signal of the pair of complementary current signals from the DAC, the first node coupled to a positive terminal of a first operational amplifier in the BBF;
• a second node configured to receive a second current signal of the pair of complementary current signals from the DAC, the second node coupled to a negative terminal of the first operational amplifier in the BBF;
• first and second resistors coupled in series across the first node the second node;
• a third node disposed between the first and second resistors and outputting a common mode voltage;
• a second operational amplifier configured to receive the common mode voltage and a common-mode reference voltage, and output a difference voltage at an output terminal;
• first and second transistors, wherein drain terminals of the first and second transistors are coupled to the first and second nodes, respectively, and
• wherein gate terminals of the first and second transistors are connected to the output terminal of the second operational amplifier.