Low Headroom X-Bridge Transconductor

A method for developing an input signal for an electronic device, the method comprising:

• providing a positive power supply voltage at a positive rail;
• providing a negative power supply voltage at a negative rail;
• developing at a pair of voltage inputs, one of inverting and one non-inverting, a differential voltage input signal having a common mode voltage range from one power rail and to within a volt or less of the other power rail;
• providing a pair of cross-coupled transconductor circuits, each transconductor circuit including:
• i. a source voltage follower responsive to one of the voltage inputs for sourcing relatively unbounded output current at unity voltage gain,
• ii. a sink voltage follower responsive to the other voltage input for sinking relatively unbounded output current to a current output terminal, and a transconductance resistor connected between the source voltage follower and the sink voltage follower for developing a differential output current, developing the differential output current with the cross-coupled transconductor circuits so as to be substantially constant over the range of the differential voltage input without limiting the differential output current.

An input circuit for an electronic device comprising:

• means for providing a positive power supply voltage at a positive rail;
• means for providing a negative power supply voltage at a negative rail;
• means for developing at a pair of voltage inputs, one of inverting and one non-inverting, a differential voltage input signal having a common mode voltage range from one power rail and to within a volt or less of the other power rail;
• means for providing a pair of cross-coupled transconductor circuits, each transconductor circuit including:
• i. a source voltage follower responsive to one of the voltage inputs for sourcing relatively unbounded output current at unity voltage gain,
• ii. a sink voltage follower responsive to the other voltage input for sinking relatively unbounded output current to a current output terminal, and a transconductance resistor connected between the source voltage follower and the sink voltage follower for developing a differential output current, and
• iii. means for developing the differential output current with the cross-coupled transconductor circuits so as to be substantially constant over the range of the differential voltage input without limiting the differential output current.