An example apparatus includes: a first voltage source, a first amplifier having a noninverting input adapted to be coupled to a photodiode anode and coupled to the first voltage source, an inverting input adapted to be coupled to a photodiode cathode, and an output, a first resistor coupled to the first amplifier inverting input and to the first amplifier output, a first capacitor coupled to the inverting input of the first amplifier and the first amplifier output, and a second voltage source different from the first voltage source. There is a second amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to the output of the first amplifier, the inverting input is coupled to the second voltage source, and there is a second resistor coupled to the inverting input and the output of the second amplifier.

A measuring current generation circuit coupled to a setting resistor is disclosed. The generation circuit includes a first measuring terminal, a second measuring terminal, a first transconductance amplifier, a second transconductance amplifier and an output circuit. The first transconductance amplifier has a first input terminal and a second input terminal. The first input terminal is coupled to one terminal of the setting resistor. The second input terminal is coupled to another terminal of the setting resistor and coupled to the first measuring terminal. The second transconductance amplifier has a third input terminal and a fourth input terminal. The output circuit is coupled to output terminals of the first transconductance amplifier and the second transconductance amplifier respectively and has a first output terminal and a second output terminal. The first output terminal is coupled to the first input terminal. The second output terminal is coupled to the second measuring terminal.

A differential amplifier is provided. The differential amplifier includes: a differential input circuit, adjusting a second current and a third current flowing into the differential input circuit according to a first input voltage, a second input voltage, and a first current; a first current source circuit, generating the first current according to a first reference voltage; a current-mirror circuit, generating a fifth current according to a fourth current; a second current source circuit, generating a sixth current and a seventh current according to a second reference voltage; and an impedance circuit, coupled to the current-mirror circuit and a ground terminal, the differential amplifier having a low output voltage error.

An example apparatus includes: a first voltage source, a first amplifier having a noninverting input adapted to be coupled to a photodiode anode and coupled to the first voltage source, an inverting input adapted to be coupled to a photodiode cathode, and an output, a first resistor coupled to the first amplifier inverting input and to the first amplifier output, a first capacitor coupled to the inverting input of the first amplifier and the first amplifier output, and a second voltage source different from the first voltage source. There is a second amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to the output of the first amplifier, the inverting input is coupled to the second voltage source, and there is a second resistor coupled to the inverting input and the output of the second amplifier.

A measuring current generation circuit coupled to a setting resistor is disclosed. The generation circuit includes a first measuring terminal, a second measuring terminal, a first transconductance amplifier, a second transconductance amplifier and an output circuit. The first transconductance amplifier has a first input terminal and a second input terminal. The first input terminal is coupled to one terminal of the setting resistor. The second input terminal is coupled to another terminal of the setting resistor and coupled to the first measuring terminal. The second transconductance amplifier has a third input terminal and a fourth input terminal. The output circuit is coupled to output terminals of the first transconductance amplifier and the second transconductance amplifier respectively and has a first output terminal and a second output terminal. The first output terminal is coupled to the first input terminal. The second output terminal is coupled to the second measuring terminal.

A differential amplifier is provided. The differential amplifier includes: a differential input circuit, adjusting a second current and a third current flowing into the differential input circuit according to a first input voltage, a second input voltage, and a first current; a first current source circuit, generating the first current according to a first reference voltage; a current-mirror circuit, generating a fifth current according to a fourth current; a second current source circuit, generating a sixth current and a seventh current according to a second reference voltage; and an impedance circuit, coupled to the current-mirror circuit and a ground terminal, the differential amplifier having a low output voltage error.

Techniques are described for ground-intermediating buffering that can effectively use the reference grounds of the circuit domains on either side of a buffer stage to generate one or more intermediated grounds for one or more signal buffers. For example, one of the reference grounds has a first amount of ground noise, the other of the reference grounds has a second amount of ground noise that is greater than or less than the first amount, and the intermediated grounds are generated to have respective amounts of ground noise that are between the first and second amounts. The ground intermediating buffer can perform signal buffering with respect to the intermediated ground(s), thereby reducing ground noise coupling across the circuit domains through both the signal and ground paths of the buffer stage.

Techniques are described for ground-intermediating buffering that can effectively use the reference grounds of the circuit domains on either side of a buffer stage to generate one or more intermediated grounds for one or more signal buffers. For example, one of the reference grounds has a first amount of ground noise, the other of the reference grounds has a second amount of ground noise that is greater than or less than the first amount, and the intermediated grounds are generated to have respective amounts of ground noise that are between the first and second amounts. The ground intermediating buffer can perform signal buffering with respect to the intermediated ground(s), thereby reducing ground noise coupling across the circuit domains through both the signal and ground paths of the buffer stage.

Techniques are described for ground-intermediating buffering that can effectively use the reference grounds of the circuit domains on either side of a buffer stage to generate one or more intermediated grounds for one or more signal buffers. For example, one of the reference grounds has a first amount of ground noise, the other of the reference grounds has a second amount of ground noise that is greater than or less than the first amount, and the intermediated grounds are generated to have respective amounts of ground noise that are between the first and second amounts. The ground intermediating buffer can perform signal buffering with respect to the intermediated ground(s), thereby reducing ground noise coupling across the circuit domains through both the signal and ground paths of the buffer stage.

A compensation circuit of a power amplifier includes a varactor, a voltage sensor and a control circuit. The varactor is coupled to an input terminal of the power amplifier. The voltage sensor is arranged for detecting an amplitude of an input signal of the power amplifier to generate a detecting result. The control circuit is coupled to the varactor and the voltage sensor, and is arranged for controlling a bias voltage of the varactor to adjust a capacitance of the varactor according to the detecting result.