A wideband variable gain amplifier (VGA) having a low phase change is disclosed. The first VGA amplifies an input signal by a current steering manner so that an amplification gain is variable. The larger a variable gain amount of the first output signal amplified by the first VGA is, the more a relative phase change amount gradually increases in either positive direction or negative direction. The second VGA further amplifies the first amplified output signal in the current steering manner so as to vary the amplification gain. As a variable gain amount of a second output signal amplified by the second VGA becomes larger, a relative phase change amount gradually increases in a direction opposite to the phase change direction of the first VGA. This opposing phase changes of the first and second VGAs are canceled against each other to provide a variable amplification gain over the wideband frequency range with a low phase change.

The present invention is directed to electrical circuits and techniques thereof. In various embodiments, the present invention provides a variable gain amplifier architecture that includes a continuous-time linear equalizer (CTLE) section and a variable gain amplifier (VGA) section. The CTLE section provides both a pair of equalized data signals and a common mode voltage. A DAC generates a control signal based on a control code. The VGA section amplifies the pair of equalized data signals by an amplification factor using a transistor whose resistance value is based on both the common mode voltage and the control signal. There are other embodiments as well.

In conventional optical receivers the dynamic range is obtained by using variable gain amplifiers (VGA) with a fixed trans-impedance amplifier (TIA) gain. To overcome the SNR problems inherent in conventional receivers an improved optical receiver comprises an automatic gain control loop for generating at least one gain control signal for controlling gain of both the VGA and the TIA. Ideally, both the resistance and the gain of the TIA are controlled by a gain control signal.

A transimpedance amplifier includes a variable gain circuit configured to generate a pair of complementary signals in accordance with an input signal and a reference signal. A first differential circuit of the variable gain circuit includes a first transistor including a control terminal to receive the input signal, a second transistor including a control terminal to receive the reference signal, and a variable resistance circuit including a first field effect transistor (FET) and a second FET. A first timing when a voltage of a first linearity adjustment signal input to the first FET reaches a first threshold voltage of the first FET and a second timing when a voltage of a second linearity adjustment signal input to the second FET reaches a second threshold voltage of the second FET are different from each other.

Systems and methods for suppressing transient outputs from an amplifier system are provided. An amplifier having a plurality of bias levels may be controlled to initiate a change in the level of a bias signal provided to the amplifier. The level of the bias signal is ramped from an initial bias level to a final bias level over numerous steps. The steps include at least one step in which the level of the bias signal is between the initial bias level and the final bias level. An amplifier system having multiple stages may be controlled to enable each stage and selectively couple each stage in a sequence that couples an output stage to an output terminal at the completion of the sequence.

In accordance with embodiments of the present disclosure, a system may include a buffer and a switch coupled between the buffer and a voltage supply such that the switch controls a varying voltage at a varying voltage node coupled to the buffer.

A circuit comprises an amplifier network including a first amplifier and a second amplifier and a first transistor having a first base. The first transistor is thermally isolated from the second amplifier. The circuit further comprises a second transistor having a second base. The second transistor is thermally linked to the second amplifier. The circuit further comprises coupling circuitry configured to couple the first base to the second base.

In conventional optical receivers the dynamic range is obtained by using variable gain amplifiers (VGA) with a fixed trans-impedance amplifier (TIA) gain. To overcome the SNR problems inherent in conventional receivers an improved optical receiver comprises an automatic gain control loop for generating at least one gain control signal for controlling gain of both the VGA and the TIA. Ideally, both the resistance and the gain of the TIA are controlled by a gain control signal.

In accordance with embodiments of the present disclosure, a system may include a buffer and a switch coupled between the buffer and a voltage supply such that the switch controls a varying voltage at a varying voltage node coupled to the buffer.

This invention relates to a optical receiver circuit (200) comprising: at least one photo detector (207) configured to convert a received light signal to an input current signal, a transimpedance amplifier circuit (201) with an input to receive the input current signal from the at least one photo detector (207) and being configured to convert the received input current signal to an output voltage signal to generate an output signal of the transimpedance amplifier circuit (201), wherein the transimpedance amplifier circuit comprises a plurality of gain amplifier stages (209, 210, 211), a DC restoration component (205), wherein the DC restoration component (205) is configured to receive the output voltage signal of the transimpedance amplifier circuit (201) for restoring the DC component of the received current signal and configured for outputting a corresponding current signal, and an automatic gain control component (204) configured for controlling via at least one programmable feedback resistor (226, 227) the equivalent transimpedance of the transimpedance amplifier circuit based on the signal output by the DC restoration component (205) to provide a constant output voltage amplitude for different current ranges of the input current signal.