An object of the disclosure is to provide a slope enhancement circuit, comprising an amplifier and a specific arrangement of capacitors and switches, further comprising a current digital to analog converter (IDAC), in a switched regulated current mirror. A method of sample and hold exploits the transient dynamics of the switched current mirror, to enhance the output current slope during PWM operation. A further object of the disclosure is to provide a low power, high speed switching type of regulated current mirror architecture. Still further, another object of the disclosure is to provide quick response to a sudden demand in current with a high degree of accuracy. Still further, another object of the disclosure is to provide a significant savings in circuit area.

Design of ultra broadband transimpedance amplifiers (TIA) for optical fiber communications is disclosed. In one embodiment, a TIA comprises a g.sub.m-boosted dual-feedback common-base stage, a level shifter and an RC-degenerated common-emitter stage, and a first emitter-follower stage, wherein the first emitter follower stage is inductively degenerated. An output of the TIA is buffered using a second emitter-follower stage.

Design of ultra broadband transimpedance amplifiers (TIA) for optical fiber communications is disclosed. In one embodiment, a TIA comprises a g.sub.m-boosted dual-feedback common-base stage, a level shifter and an RC-degenerated common-emitter stage, and a first emitter-follower stage, wherein the first emitter follower stage is inductively degenerated. An output of the TIA is buffered using a second emitter-follower stage.

A first circuit unit of an audio amplifier includes a first emitter follower connected to an pre stage input terminal, a second emitter follower connected to an pre stage input terminal, a main transistor connected to an output path of the first emitter follower and an output path of the second emitter follower, a first resistor and a second resistor, which are series-connected between the output path of the first emitter follower and a DC voltage source, and a zener diode connected to a series-connection point between the first resistor and the second resistor. A second circuit unit has a circuit configuration that is complementary to the first circuit unit. A path leading to a collector of each transistor configuring the first and second emitter followers in one of the circuit units is connected to the series-connection point in the other circuit unit.

A first circuit unit of an audio amplifier includes a first emitter follower connected to an pre stage input terminal, a second emitter follower connected to an pre stage input terminal, a main transistor connected to an output path of the first emitter follower and an output path of the second emitter follower, a first resistor and a second resistor, which are series-connected between the output path of the first emitter follower and a DC voltage source, and a zener diode connected to a series-connection point between the first resistor and the second resistor. A second circuit unit has a circuit configuration that is complementary to the first circuit unit. A path leading to a collector of each transistor configuring the first and second emitter followers in one of the circuit units is connected to the series-connection point in the other circuit unit.

Provided is a condenser microphone circuit that can support variation in power supply voltage of a phantom power supply using a wiring system of two lines. A condenser microphone circuit includes a microphone unit, an FET, a constant current diode, a collector grounding first transistor that generates an operation power supply of the FET, a first resistor that sets base potential of the first transistor, a collector grounding second transistor that amplifies an output signal from the FET, a second resistor that sets base potential of the second transistor, and an output circuit. A base of the first transistor is connected to a source of the FET, an emitter of the first transistor is connected to a drain of the FET, a base of the second transistor is connected to the drain of the FET, an emitter of the second transistor is connected to the output circuit, and the second resistor divides voltage on a cathode side of the constant current diode.

The disclosed technology relates to a method for improving performance of a feedback circuit comprising an amplifier and a feedback network, wherein the feedback circuit has at least one tunable component. In one aspect, the method comprises measuring first amplitude values at an input of the amplifier and second amplitude values at an output of the amplifier, estimating a linear open-loop gain of the amplifier based on both the amplitude values, estimating a linear finite gain error based on the estimated gain and the second amplitude values, subtracting the linear finite gain error from the first amplitude values to derive a set of samples containing second error information, deriving an signal-to-noise-plus-distortion ratio estimate based on the variance of the set of samples and a variance of the second amplitude values, and adjusting the feedback circuit in accordance with the signal-to-noise-plus-distortion ratio estimate.

A transconductance circuit has an input terminal (V.sub.IN) and an output terminal (Out), a first current source (4) having a gate connected to said input terminal (V.sub.IN); and a second current source (5), in parallel with said first current source, and having a higher transconductance and a wider dynamic range than the first current source. The current sources are configured so that at a low input voltage only the first current source (4) is on. A voltage drop circuit provides a lower bias voltage for the second current source than for the first current source.

A power amplifier bias circuit with embedded envelope detection includes a bias circuit stage coupled to an envelope detector circuit to increases a bias provided to a power amplifier as a function of an incoming envelope signal. The envelope detector circuit includes a first source/emitter follower transistor, a current source, and a filter to generate a baseband envelope signal. The current source is coupled to an output node of the first source/emitter follower transistor and the filter is also coupled to the output node of the first source/emitter follower transistor. The bias circuit stage includes one or more replica transistors that replicate transistors of the power amplifier or power amplifier core stage, an envelope detector replica transistor and a replica of the current source of the envelope detector circuit.

A bidirectional amplifier includes first and second ports, with a first summing node connected to the first port and a second summing node connected to the second port. First and second gain stages are connected between the first and second summing nodes, respectively, and a first node. First and second feedback stages are also connected between the first and second summing nodes, respectively, and the first node. The amplifier operates in a first mode in which an amplified version of a signal applied to the first port is provided at the second port, or a second mode in which an amplified version of a signal applied to the second port is provided at the first port. The first and second gain stages are preferably first and second common emitter cascode arrangements, and the first and second feedback stages are preferably first and second emitter followers.