A RF control circuit is provided and includes a controller, a divider, and a RF sensor. The controller selects a RF, which is a frequency of a reference LO signal. The divider receives a first RF signal detected in a substrate processing chamber and outputs a second RF signal. The first RF signal is generated by a RF generator and supplied to the substrate processing chamber. The RF sensor includes a lock-in amplifier, which includes: a RF path that receives the second RF signal; a LO path that receives the reference LO signal; a first mixer that generates an IF signal based on the second RF signal and the reference LO signal; and a filter that filters the IF signal. The controller generates a control signal based on the filtered IF signal and transmits the control signal to the RF generator to adjust the first RF signal.

A RF control circuit is provided and includes a controller, a divider, and a RF sensor. The controller selects a RF, which is a frequency of a reference LO signal. The divider receives a first RF signal detected in a substrate processing chamber and outputs a second RF signal. The first RF signal is generated by a RF generator and supplied to the substrate processing chamber. The RF sensor includes a lock-in amplifier, which includes: a RF path that receives the second RF signal; a LO path that receives the reference LO signal; a first mixer that generates an IF signal based on the second RF signal and the reference LO signal; and a filter that filters the IF signal. The controller generates a control signal based on the filtered IF signal and transmits the control signal to the RF generator to adjust the first RF signal.

Single controller automatic calibrating circuits for reducing or canceling offset voltages in operational amplifiers (op-amps) in an instrumentation amplifier are disclosed. An automatic calibrating op-amp system is provided that includes an instrumentation amplifier, which includes a front-end amplifier circuit comprising at least one front-end op-amp and a final-stage amplifier circuit comprising a final-stage op-amp. The op-amp(s) can include auxiliary differential inputs for offset voltage cancellation. The automatic calibrating op-amp system also includes an automatic calibration circuit employing a single controller to generate calibration signals on a calibration output to an auxiliary differential input(s) of an op-amp(s) in the instrumentation amplifier for offset voltage cancellation. The automatic calibration circuit includes a single controller to generate calibration signals to the instrumentation amplifier to reduce or cancel offset voltage, thereby eliminating the need to provide multiple automatic calibration circuits or an automatic calibration circuit employing multiple controllers.

An apparatus for power amplifier control is provided, applied to a multi-stage power amplifier. The apparatus controls an input voltage of an amplification triode in the first amplification stage, by using a detected current change at a base of an amplification triode in the last amplification stage, achieving control of output power and a maximum output current of the multi-stage power amplifier, greatly reducing an influence of current detection on maximum output power and maximum output efficiency of the power amplifier.

One example includes a differential amplifier, a voltage weighting element, coupled to a voltage source which provides an input voltage, to provide a reference voltage with a constant power limit when the input voltage varies, an error amplifier configured to receive and compare the reference voltage provided from the voltage weighting element and a feedback sensed voltage provided from the differential amplifier to identify whether the sensed voltage exceeds the reference voltage, and a pulse width modulation (PWM) controller, coupled to a power transformer and the error amplifier, that reduces a transformer input current provided to the power transformer based on the comparison of the reference voltage from the voltage weighting element and the feedback sensed voltage from the differential amplifier.

A preamplifier for musical instruments includes: an operational amplifier 40 to amplify an inputted analog audio signal; a dual-unit variable resistor 30 to change an amplification factor of the operational amplifier 40 by manually operating an operation unit; an A/D converter 51 to convert the amplified analog audio signal to a digital audio signal; and a digital signal processor 60 to digital-signal process the digital audio signal, wherein the dual-unit variable resistor 30 includes a second variable resistor 32 to output a detection signal in accordance with an amount of operation of the operation unit, and the digital signal processor 60 is capable of implementing, based on a value of the detection signal, a first digital gain process to amplify the digital audio signal and/or a second digital gain process to attenuate the digital audio signal.

In a general aspect, a system can include a fully differential amplifier circuit that includes a first amplifier, and first and second feedback paths. The first feedback path can provide a feedback path from a positive output of the first amplifier to a negative input of the first amplifier. The second feedback path can provide a feedback path from a negative output of the first amplifier to a positive input of the first amplifier. The system can include a chopper clock circuit configured to output a variable duty cycle chopper clock signal. The system can include a common mode loop circuit including a second amplifier and chopper switches. The common mode loop circuit can be configured as a local feedback loop for the first amplifier. The chopper switches can be configured to receive the chopper clock signal and control current flow into the positive and negative inputs.

A circuit includes a pair of high side transistors, a pair of low side transistors, a first sense resistor coupled to one of the low side transistors at a first sense node, and a second sense resistor coupled to another of the low side transistors at a second sense node. The first and second sense resistors couple together at a ground node. The circuit includes a first switch network coupled to the first sense resistor, a second switch network coupled to the second sense resistor, a first pair of switches configured to selectively provide a potential of the ground node or a potential of the first sense node as a ground potential to the first switch network, and a second pair of switches configured to selectively provide the potential of the ground node or a potential of the second sense node as a ground potential to the second switch network.

An amplifier system may include a first feedback loop coupled between an output of an amplifier to an input of a modulator for regulating an output voltage driven at the output of the amplifier to a first terminal of a load of the amplifier system, a sense resistor for sensing a physical quantity associated with the amplifier, a second control loop coupled to the sense resistor such that the sense resistor is outside of the second control loop, the second control loop configured to regulate a common-mode voltage at a second terminal of the load, and a common-mode feedforward circuit coupled to the sense resistor and configured to minimize effects of a signal-dependent common-mode feedback of the sense resistor.

One example includes a differential amplifier, a voltage weighting element, coupled to a voltage source which provides an input voltage, to provide a reference voltage with a constant power limit when the input voltage varies, an error amplifier configured to receive and compare the reference voltage provided from the voltage weighting element and a feedback sensed voltage provided from the differential amplifier to identify whether the sensed voltage exceeds the reference voltage, and a pulse width modulation (PWM) controller, coupled to a power transformer and the error amplifier, that reduces a transformer input current provided to the power transformer based on the comparison of the reference voltage from the voltage weighting element and the feedback sensed voltage from the differential amplifier.