Linearity correction in high voltage transmit switches

An ultrasonic transceiver system, comprising:

• a transducer;
• ultrasonic receiver circuitry, coupled to the transducer;
• ultrasonic transmitter circuitry, having an output terminal coupled to the transducer;
• a transmit/receive switch, coupled to the ultrasonic transmitter circuitry and to the ultrasonic receiver circuitry, and configured to isolate the ultrasonic receiver circuitry from the ultrasonic transmitter circuitry while the ultrasonic transmitter circuitry is transmitting;
• wherein the ultrasonic transmitter circuitry comprises:
• a linear amplifier, comprising:
• a first amplifier stage having a signal input, a feedback input, and an output;
• and
• a second amplifier stage having an input and an output, the input of the second amplifier stage coupled to the output of the first amplifier stage;
• an output stage having an input and an output, the input of the output stage coupled to the output of the second amplifier stage, and the output of the output stage coupled to the feedback input of the first amplifier stage;
• a transistor having a first current path terminal coupled to the output of the second amplifier stage and the input of the output stage;
• control circuitry having a first terminal coupled to a control terminal of the transistor;
• a current compensation circuit having a current terminal and a control terminal, the current terminal of the current compensation circuit coupled to the output of the first amplifier stage and the input of the second amplifier stage;
• and
• a multiplexer having a first terminal coupled to a second current path terminal of the transistor, having a second terminal coupled to the control terminal of the current compensation circuit, and having a third terminal coupled to a bias terminal of the ultrasonic transmitter circuitry, the multiplexer configured to couple the second current path terminal of the transistor to the bias terminal responsive to the transistor turning on, and to couple the second current path terminal of the transistor to the control terminal of the current compensation circuit responsive to the transistor turning off.

A method, comprising:

• generating a first signal with a transconductance amplifier;
• amplifying the first signal with a driver stage, thereby generating a second signal;
• generating an output signal responsive to the second signal with an output stage, the output stage having an output coupled to a transducer;
• turning off a transistor in response to initiating a transmit interval, the transistor having a first current path terminal coupled to an output of the driver stage;
• coupling a second current path terminal of the transistor to a control terminal of a compensation circuit with a multiplexer in response to turning off the transistor;
• sensing a current through the first and second current path terminals of the transistor with the compensation circuit in response to coupling the second current path terminal of the transistor to the control terminal of the compensation circuit;
• generating a compensation current responsive to the sensed current with the compensation circuit;
• and
• modifying the first signal with the compensation current.