A voltage controlled amplifier with an amplitude limiting circuit, such as a clip limiter, that is separate from the signal path on which the input signal is received by a power amplifier can reduce both noise and power expenditure of the voltage controlled amplifier. The amplitude limiting circuit can include a transistor network that is controlled by a pair of utility operational amplifiers. These utility amplifiers may use less current than the audio amplifier of the voltage controlled amplifier. Further, the transistor network can be deactivated when a signal supplied to the voltage controlled amplifier is below a clipping or other voltage limiting threshold.

A boosted amplifier system may include a boost stage configured to boost an input voltage of the boost stage to an output voltage greater than the input voltage and an amplifier stage powered by the output voltage of the charge pump and configured to amplify an input signal to generate an output signal. The boost stage may have input current limiting circuitry for ensuring that an input current of the boost stage is maintained below a current limit and the amplifier stage may have an input for receiving an indication of whether the current-limiting circuitry of the boost stage is activated to maintain the input current of the boost stage below the current limit.

One embodiment is an apparatus including a detector circuit electrically coupled between a signal source and a second circuit, the signal source generating a first signal, the detector circuit detecting a level of the first signal and generating a first control signal when the detected level of the first signal exceeds a first threshold value, and a clamping switch electrically coupled to receive the first control signal from the detector circuit, the clamping switch including a multi-terminal active device. The first control signal controls a state of the clamping switch such that the clamping switch clamps a level of a signal applied to the second circuit when the level of the first signal exceeds the first threshold value.

A voltage controlled amplifier with an amplitude limiting circuit, such as a clip limiter, that is separate from the signal path on which the input signal is received by a power amplifier can reduce both noise and power expenditure of the voltage controlled amplifier. The amplitude limiting circuit can include a transistor network that is controlled by a pair of utility operational amplifiers. These utility amplifiers may use less current than the audio amplifier of the voltage controlled amplifier. Further, the transistor network can be deactivated when a signal supplied to the voltage controlled amplifier is below a clipping or other voltage limiting threshold.

One embodiment is an apparatus including a detector circuit electrically coupled between a signal source and a second circuit, the signal source generating a first signal, the detector circuit detecting a level of the first signal and generating a first control signal when the detected level of the first signal exceeds a first threshold value, and a clamping switch electrically coupled to receive the first control signal from the detector circuit, the clamping switch including a multi-terminal active device. The first control signal controls a state of the clamping switch such that the clamping switch clamps a level of a signal applied to the second circuit when the level of the first signal exceeds the first threshold value.

One embodiment is an apparatus including a detector circuit electrically coupled between a signal source and a second circuit, the signal source generating a first signal, the detector circuit detecting a level of the first signal and generating a first control signal when the detected level of the first signal exceeds a first threshold value, and a clamping switch electrically coupled to receive the first control signal from the detector circuit, the clamping switch including a multi-terminal active device. The first control signal controls a state of the clamping switch such that the clamping switch clamps a level of a signal applied to the second circuit when the level of the first signal exceeds the first threshold value.

A current feed-back instrumentation amplifier (CFIA) comprises a differential pair with degeneration for amplifying small differential voltages in the presence of large common-mode voltages. The CFIA includes input and feedback transconductors and a trimming circuit that trims the back-bias voltages of the transistors in each transconductor. The trimming circuit includes a plurality of selectable resistors disposed in the signal path of the tail current in each transconductor. Each of the plurality of selectable resistors has a switch coupled to it. When a switch is closed, only the resistors up to the respective switch are in the signal path of the bulk-to-source voltage of the differentially paired transistors. The resistor trimming circuit reduces the mismatch between transconductances of the respective differential pair transistors, in turn reducing mismatch of the overall transconductances of the transconductors, and thereby reducing the CFIA's gain error.

One embodiment is an apparatus including a detector circuit electrically coupled between a signal source and a second circuit, the signal source generating a first signal, the detector circuit detecting a level of the first signal and generating a first control signal when the detected level of the first signal exceeds a first threshold value, and a clamping switch electrically coupled to receive the first control signal from the detector circuit, the clamping switch including a multi-terminal active device. The first control signal controls a state of the clamping switch such that the clamping switch clamps a level of a signal applied to the second circuit when the level of the first signal exceeds the first threshold value.

A current feed-back instrumentation amplifier (CFIA) comprises a differential pair with degeneration for amplifying small differential voltages in the presence of large common-mode voltages. The CFIA includes input and feedback transconductors and a trimming circuit that trims the back-bias voltages of the transistors in each transconductor. The trimming circuit includes a plurality of selectable resistors disposed in the signal path of the tail current in each transconductor. Each of the plurality of selectable resistors has a switch coupled to it. When a switch is closed, only the resistors up to the respective switch are in the signal path of the bulk-to-source voltage of the differentially paired transistors. The resistor trimming circuit reduces the mismatch between transconductances of the respective differential pair transistors, in turn reducing mismatch of the overall transconductances of the transconductors, and thereby reducing the CFIA's gain error.

An amplification system can include a bias booster circuit and an amplifier that amplifies an input signal to drive a load. The bias boosting circuit can include a negative bias booster that applies a charge to an input node of the amplifier in response to a negative half-cycle of the input signal that exceeds a boost threshold level. The bias boosting circuit can also include a positive bias booster that discharges the input node of the amplifier during a positive half-cycle of the input signal that exceeds the boost threshold level. The discharging by the positive bias booster is slower than the charging by the negative bias booster to induce a bias voltage increase from a quiescent bias voltage on the input node of the amplifier.