This disclosure relates to the field of amplifiers for multi-level optical communication and more particularly to techniques for trans-impedance amplifiers (TIA) with gain control. The claimed embodiments address the problem of implementing a low cost TIA that exhibits high linearity, low noise, low power, and wide bandwidth. More specifically, some claims are directed to approaches for providing TIA gain control using a plurality of inverter-based replica gain control cells controlled by a feedback loop to manage the current into the amplifying output stage and thereby the TIA output voltage.

Methods and circuits for maximizing gain of a voltage follower circuit are provided. The method includes using a NMOS voltage replica generation circuit, a PMOS voltage replica generation circuit, a NPN BJT voltage replica generation circuit, a n-channel JFET voltage replica generation circuit, a P-Channel JFET voltage replica generation circuit and a PNP BJT voltage replica generation circuit. The overall gain for the various transistor families is almost equal to unity.

A method and system for amplifying small optical currents in an optical receiver front end system may employ multiple transimpendance amplifiers (TIAs) and feedback control loops. For example, the front end system may include a main feedback control loop (having a main TIA) and a replica feedback control loop (having a replica TIA) that, collectively, generate an optimum input common mode level for a differential amplifier operating at high data rates (e.g., speeds up to tens of gigabits per second). The replica TIA may track the noise from the power supply of the optical receiver in the substantially same manner as the main TIA. Therefore, the differential signals produced by the main control loop may not be degraded at the input to the high-speed differential amplifier. The outputs of the high-speed differential amplifier may be symmetric about the common mode level and may be suitable inputs for voltage sampling.

A circuit includes a bias circuit for a biased transistor. The bias circuit includes a master-slave source follower circuit, a reference transistor, and a bias circuit voltage output coupled to the biased transistor and configured to provide a bias voltage. The reference transistor has a transconductance substantially identical to a transconductance of the biased transistor. A signal ground circuit may be coupled between the biased transistor and one or more components of the bias circuit that do not generate significant return currents to a power supply ground. A method includes generating a current in a reference transistor according to a first voltage generated using a master source follower circuit, generating a second voltage substantially identical to the first voltage using a slave source follower circuit, and providing the second voltage to a biased transistor. The reference transistor has a transconductance substantially identical to a transconductance of the biased transistor.

A digital-to-analog converter (DAC) may include a conversion block providing a first analog value. The DAC may also include an amplification block for receiving the first analog value and providing a second analog value amplified by an amplification factor. The amplification block may include a first input terminal for receiving the first analog value, a second input terminal, and an output terminal for providing the second analog value. The amplification block may also include a first capacitive element and a second capacitive element. The first and second capacitive elements may determine the amplification factor. The amplification block may further include a control unit for recovering a charge at a first terminal of the second capacitive element, and based thereon, the second analog value.

A transmitter circuit comprises: an input, an encoder circuit, and a transmitter. During operation, the transmitter circuit receives an input signal. The encoder circuit encodes the received input signal into an encoded signal. The encoder circuit produces the encoded signal: i) to indicate changing states of the input signal, and ii) to include a supplemental transient signal with respect to the received input signal. The transmitter transmits the encoded signal from an output of the first circuit over a link to a second circuit such as a receiver circuit. A receiver decodes the encoded signal to reproduce a rendition of the input signal to control remote power supply circuitry. Presence of the supplemental transient signal in the encoded signal indicates to the receiver circuit that the first circuit actively transmits the output signal even though there may not be any change to a current state of the input signal.

A peak detector using a charge pump is provided. The peak detector includes a differential amplifier configured to receive an input signal to be detected through an input node and amplify the received signal; a current control logic configured to create two or more current control signals by comparing a signal output from the differential amplifier with two or more reference voltages; a mirror current source portion comprising two or more mirror current sources configured to be driven respectively by the current control signals from the current control logic; a capacitor configured to be charged or discharged by currents output from the mirror current sources; and a reset circuit configured to reset a voltage of the capacitor.

A bias circuit comprises: a first circuit that comprises a first resistor and a decoupling capacitor; a bias voltage generation circuit that comprises a first transistor being connected to the first circuit; one or more switches; a first replica circuit comprising a second circuit and a second transistor, the second circuit comprising a second resistor and a capacitor, the second transistor being connected to the second circuit; a second replica circuit comprising a third transistor; a comparator that makes a comparison between a pseudo-bias voltage and a reference voltage; and a control circuit that controls the one or more switches on the basis of the comparison result to reduce the amount of the current flowing through the first transistor.

Embodiments herein include a replica communication path and monitor circuit to provide increased common mode transient immunity. As its name suggests, the monitor circuit monitors the replica communication path and produces an adjustment signal (common mode transient adjustment signal) to cancel presence of a common mode transient signal in one or more other communication paths conveying data signals.

The disclosure relates to a system and method for controlling a common mode voltage of an output differential signal of a differential signal processing circuit using a replica circuit and feedback control. The differential signal processing circuit includes two load devices, two input transistors, and two current-source transistors coupled in series between voltage rails, respectively. The replica circuit includes replica load device, replica input transistor, and replica current-source transistor coupled in series between the voltage rails. The common mode voltage of the input differential signal is applied to the replica input transistor to generate a replica output common mode voltage. A feedback circuit generates a bias voltage for the replica current-source transistor and the current-source transistors of the differential circuit to set and control the replica output common mode voltage and the output common mode voltage of the differential signal processing circuit to a target common mode voltage.