A system for split-frequency amplification, preferably including: one or more primary-band amplification stages, one or more secondary-band amplification stages, one or more band-splitting filters, and/or one or more signal couplers. An analog canceller including one or more split-frequency amplifiers. A mixer including one or more split-frequency amplifiers. A voltage-controlled oscillator including one or more split-frequency amplifiers. A method for split-frequency amplification, preferably including: receiving an input signal, separating the input signal into signal portions, and/or amplifying the signal portions, and optionally including combining the amplified signal portions and/or providing one or more output signals.

An operational amplifier includes a voltage terminal; a common terminal; a first amplification stage for receiving a differential signal pair to generate a single-end amplification signal; a first buffer for generating a first voltage according to the single-end amplification signal; a first diode for reducing the first voltage to generate a second voltage; a second amplification stage for amplifying the second voltage to generate a third voltage; a voltage stabilizing circuit for stabilizing the third voltage; a second diode coupled between the second amplification stage and the common terminal; a second buffer for generating an output voltage according to the third voltage; and a current mirror coupled to the common terminal, the first amplification stage, the first diode and the second amplification stage.

A microphone system includes a microphone and a pre-amplification conditioning circuit configured within a housing and comprising a pair of matched JFETs configured in a differential pair with common-source configuration and, when biased, are operable to receive and amplify the differential microphone output signal. The microphone further includes a pair of BJTs configured as a complimentary feedback transistor pair with each of the pair of BJTs coupled in parallel to a corresponding one of the pair of matched JFETs, and a current sink coupled to the matched JFETs and corresponding emitter electrodes of the BJTs and operable to maintain a fixed total direct current through each of the matched JFETs and BJTs, which reduces the JFETs corresponding electrical load, reduces signal noise, and increases a maximum amplified microphone output signal level at the drains of the matched JFETs.

A microphone system includes a microphone and a pre-amplification conditioning circuit configured within a housing and comprising a pair of matched JFETs configured in a differential pair with common-source configuration and, when biased, are operable to receive and amplify the differential microphone output signal. The microphone further includes a pair of BJTs configured as a complimentary feedback transistor pair with each of the pair of BJTs coupled in parallel to a corresponding one of the pair of matched JFETs, and a current sink coupled to the matched JFETs and corresponding emitter electrodes of the BJTs and operable to maintain a fixed total direct current through each of the matched JFETs and BJTs, which reduces the JFETs corresponding electrical load, reduces signal noise, and increases a maximum amplified microphone output signal level at the drains of the matched JFETs.

A system for split-frequency amplification, preferably including: one or more primary-band amplification stages, one or more secondary-band amplification stages, one or more band-splitting filters, and/or one or more signal couplers. An analog canceller including one or more split-frequency amplifiers. A mixer including one or more split-frequency amplifiers. A voltage-controlled oscillator including one or more split-frequency amplifiers. A method for split-frequency amplification, preferably including: receiving an input signal, separating the input signal into signal portions, and/or amplifying the signal portions, and optionally including combining the amplified signal portions and/or providing one or more output signals.

An operational amplifier includes a voltage terminal; a common terminal; a first amplification stage for receiving a differential signal pair to generate a single-end amplification signal; a first buffer for generating a first voltage according to the single-end amplification signal; a first diode for reducing the first voltage to generate a second voltage; a second amplification stage for amplifying the second voltage to generate a third voltage; a voltage stabilizing circuit for stabilizing the third voltage; a second diode coupled between the second amplification stage and the common terminal; a second buffer for generating an output voltage according to the third voltage; and a current mirror coupled to the common terminal, the first amplification stage, the first diode and the second amplification stage.

A system for split-frequency amplification, preferably including: one or more primary-band amplification stages, one or more secondary-band amplification stages, one or more band-splitting filters, and/or one or more signal couplers. An analog canceller including one or more split-frequency amplifiers. A mixer including one or more split-frequency amplifiers. A voltage-controlled oscillator including one or more split-frequency amplifiers. A method for split-frequency amplification, preferably including: receiving an input signal, separating the input signal into signal portions, and/or amplifying the signal portions, and optionally including combining the amplified signal portions and/or providing one or more output signals.

A system for split-frequency amplification, preferably including: one or more primary-band amplification stages, one or more secondary-band amplification stages, one or more band-splitting filters, and/or one or more signal couplers. An analog canceller including one or more split-frequency amplifiers. A mixer including one or more split-frequency amplifiers. A voltage-controlled oscillator including one or more split-frequency amplifiers. A method for split-frequency amplification, preferably including: receiving an input signal, separating the input signal into signal portions, and/or amplifying the signal portions, and optionally including combining the amplified signal portions and/or providing one or more output signals.

A variable gain amplifier circuit includes a main circuit including a differential current circuit, a current divider circuit connected to a high potential side of the differential current circuit, and a load circuit connected to a high potential side of the current divider circuit, the main circuit being configured to generate differential output voltage signals by the load circuit in accordance with either differential input voltage signals or first differential current signals; and a gain adjustment circuit configured to adjust a gain of the main circuit. The gain adjustment circuit includes a generation circuit configured to generate a first control voltage and a second control voltage in accordance with a setting signal, and a limit circuit configured to limit, by detecting an amplitude of the differential output voltage signals, the voltage difference to a limit value or greater so that the amplitude does not become lower than a setting voltage.

A circuit may include first and second input nodes, first and second output nodes, first and second intermediate nodes, first and second resistances, a first amplification transistor coupled to the first input node, the first resistance, and the first intermediate node and a second amplification transistor coupled to the second input node, the second resistance, and the second intermediate node. The circuit may also include a first active device coupled to the first output node and the first intermediate node, a second active device coupled to the second output node and the second intermediate node, a first output transistor coupled to the first output node and configured to conduct based on a second intermediate signal on the second intermediate node, and a second output transistor coupled to the second output node and configured to conduct based on a first intermediate signal on the first intermediate node.