This disclosure describes techniques for selecting one of a plurality of modes in which to operate an amplifier. The techniques include configuring input routing circuitry, coupled to first and second inputs of the amplifier, based on the selected one of the plurality of modes; selectively applying a resistance to an output of the amplifier, using feedback routing circuitry, based on the selected one of the plurality of modes; and selectively applying one of a plurality of reference voltages, using reference voltage routing circuitry, coupled to the first and the second inputs of the amplifier, based on the selected one of the plurality of modes.

This disclosure describes techniques for selecting one of a plurality of modes in which to operate an amplifier. The techniques include configuring input routing circuitry, coupled to first and second inputs of the amplifier, based on the selected one of the plurality of modes; selectively applying a resistance to an output of the amplifier, using feedback routing circuitry, based on the selected one of the plurality of modes; and selectively applying one of a plurality of reference voltages, using reference voltage routing circuitry, coupled to the first and the second inputs of the amplifier, based on the selected one of the plurality of modes.

A controlled active resistance. The active resistance is implemented on an integrated circuit. In some embodiments, the active resistance includes a MOSFET. In alternate embodiments, the active resistance includes a MOSFET and a resistor. The control for the active resistance includes a reference resistor and an operational amplifier. The control for the active resistance further includes two current sources: i) a current source producing a current that is proportional to absolute temperature, and ii) another current source that is produced by a bandgap voltage reference. In one aspect, the active resistance generates an effective resistance that is proportional to thermal voltage. In another aspect, the active resistance generates an effective resistance that is proportional to inverse of the thermal voltage. In an alternate aspect, the current sources have various dependencies, and the active resistance generates an effective resistance that is proportional to those dependencies.

An ultrasound circuit comprising a single-ended trans-impedance amplifier (TIA) is described. The TIA is coupled to an ultrasonic transducer to amplify an electrical signal generated by the ultrasonic transducer in response to receiving an ultrasound signal. The TIA is followed by further processing circuitry configured to filter, amplify, and digitize the signal produced by the TIA.

A pseudo-resistor structure, comprises: a first and a second PMOS transistor or PN diode configured as two-terminal devices, wherein the positive terminal of the first PMOS transistor or PN diode is connected to the positive terminal of the second PMOS transistor or PN diode, and wherein the negative terminal of the first PMOS transistor or PN diode is connected to an input (A) of the pseudo-resistor structure and wherein the negative terminal of the second PMOS transistor or PN diode is connected to an output (C) of the pseudo-resistor structure, and a dummy transistor or dummy diode connected to the input (A), wherein the dummy transistor or dummy diode is further connected to a bias voltage for compensating a leakage current through the first and the second PMOS transistors or PN diodes. A closed-loop operational amplifier circuit comprising the pseudo-resistor structure is provided. Also, a bio-potential sensor comprising the closed-loop operational amplifier circuit is provided.

Transimpedance amplifiers with feedforward current are provided herein. In certain embodiments, an amplifier system includes a transimpedance amplifier that amplifies an input current received at an input to generate an output voltage at an output. The amplifier system further includes a controllable current source that is coupled to the output of the transimpedance amplifier, and operable to provide a feedforward current that changes in relation to the input current of the transimpedance amplifier. By providing a feedforward current in this manner, gain and speed performance of the transimpedance amplifier is enhanced.

A controlled active resistance. The active resistance is implemented on an integrated circuit. In some embodiments, the active resistance includes a MOSFET. In alternate embodiments, the active resistance includes a MOSFET and a resistor. The control for the active resistance includes a reference resistor and an operational amplifier. The control for the active resistance further includes two current sources: i) a current source producing a current that is proportional to absolute temperature, and ii) another current source that is produced by a bandgap voltage reference. In one aspect, the active resistance generates an effective resistance that is proportional to thermal voltage. In another aspect, the active resistance generates an effective resistance that is proportional to inverse of the thermal voltage. In an alternate aspect, the current sources have various dependencies, and the active resistance generates an effective resistance that is proportional to those dependencies.

An amplifier for a receiver circuit is disclosed. The amplifier has an input node (V.sub.in) and an output node (V.sub.out). It comprises a tunable tank circuit connected to the output node (V.sub.out), a feedback circuit path connected between the output node (V.sub.out) and the input node (V.sub.in), and a tunable capacitor connected between an internal node of the feedback circuit path and a reference-voltage node. A receiver circuit and a communication apparatus is disclosed as well.

In optical receivers, extending the transimpedance amplifier's (TIA) dynamic range is a key to increasing the receiver's dynamic range, and therefore increase the channel capacity. Ideally, the TIA requires controllable gain, whereby the receiver can modify the characteristics of the TIA and/or the VGA to process high power incoming signals with a defined maximum distortion, and low power incoming signals with a defined maximum noise. A solution to the problem is to provide TIA's with reconfigurable feedback resistors, which are adjustable based on the level of power, e.g. current, generated by the photodetector, and variable load resistors, which are adjustable based on the change in impedance caused by the change in the feedback resistor.

Transimpedance amplifiers with feedforward current are provided herein. In certain embodiments, an amplifier system includes a transimpedance amplifier that amplifies an input current received at an input to generate an output voltage at an output. The amplifier system further includes a controllable current source that is coupled to the output of the transimpedance amplifier, and operable to provide a feedforward current that changes in relation to the input current of the transimpedance amplifier. By providing a feedforward current in this manner, gain and speed performance of the transimpedance amplifier is enhanced.