An avalanche photo-diode (APD) circuit includes a first APD and a bias circuit. The first APD is configured to detect light. The bias circuit is configured to control a gain of the first APD. The bias circuit includes a second APD, a reference voltage source, a bias voltage generation circuit, and a metal layer configured to shield the second APD from the light. The reference voltage source is configured to bias the second APD. The bias voltage generation circuit is configured to generate a bias voltage for biasing the first APD based on dark current output by the second APD.

An optical receiver can implement a transimpedance amplifier (TIA) to process received light using a closed loop optical pre-amplification. The optical receiver can use an average input value of the TIA to control an semiconductor optical amplifier (SOA) or pre-amplification as received average signal varies. The optical receiver can include a gain controller for the TIA that can measure the TIA swing to adjust the gain of the SOA to pre-amplify received light in a closed loop control configuration.

A receiver circuit includes an input terminal for receiving an input current signal, a transimpedance amplifier having an input node, the transimpedance amplifier converting a current signal input to the input node into a voltage signal, an inductor having a first terminal and a second terminal, and a bypass circuit. The first terminal is coupled to the input terminal and the second terminal is coupled to the input node. The bypass circuit includes a bias circuit supplying a bias voltage, a first variable resistor coupled between the first terminal and the bias circuit, a second variable resistor coupled between the second terminal and the bias circuit, and an impedance adjustment circuit including a resistor and a capacitor connected in parallel to the resistor, the impedance adjustment circuit connected in series to at least one of the first variable resistor and the second variable resistor.

This optical communication device (1) is provided with: a plurality of light-receiving elements (11) configured to receive communication light, the plurality of light-receiving elements being provided so as to correspond to a plurality of channels; and a controller (15) configured to perform control to invalidate output from a light-receiving element that has received high-intensity light higher in light intensity than a predetermined value among the plurality of light-receiving elements.

A communication system comprising a light source associated with a first item of interest; a visible light communications system operably coupled to the light source of the first item of interest, the visible light communications system configured to process information as an encoded signal and output the encoded signal via the light source; and a receiver associated with a second item of interest, the receiver configured to receive the encoded signal from the light source and process the encoded signal to obtain the information.

A transimpedance amplifier circuit (1) includes an amplifier (22) that amplifies a received signal, an automatic gain control (AGC) circuit (2) that controls the amplification gain of the amplifier by a first time constant in accordance with the level of the received signal, and a first selection circuit (25) that selects the first time constant from a plurality of predetermined values. This can simultaneously implement a short time constant of an AGC function necessary to instantaneously respond to a burst signal and a long time constant of the AGC function necessary to obtain a satisfactory bit error rate (BER) characteristic in a continuous signal by an inexpensive and compact circuit arrangement.

According to one example, errors in a logical signal from a data slicer are detected and a power supply voltage is adjusted based on the detected errors.

In order to further develop a circuit arrangement (CR; CR′) for receiving optical signals (SI) from at least one optical guide (GU), said circuit arrangement (CR; CR′) comprising: at least one light-receiving component (PD) for converting the optical signals (SI) into electrical current signals (I.sub.PD), at least one transimpedance amplifier (TA), being provided with the electrical current signals (I.sub.PD) from the light-receiving component (PD), at least one automatic gain controller (AG) for controlling the gain or transimpedance (R) of the transimpedance amplifier (TA), at least one integrator (IN) in a feedback path (FP), said integrator (IN) generating a control signal (V.sub.int), at least one voltage-controlled current source (CS), being provided with the control signal (V.sub.int) from the integrator (IN), at least one limiter (LI) acting as a comparator and generating in its output a logic level for positive or negative voltages in its input,
and a corresponding method in such a way that a multilevel optical link can be provided, at least one second transimpedance amplifier (TA2) arranged in parallel to the transimpedance amplifier (TA), and at least one automatic offset controller (AO) for setting the voltage (V.sub.offset) for the second transimpedance amplifier (TA2)
are proposed.

A digitally-controlled transimpedance amplifier (TIA) circuit is provided in which a plurality of feedback loops are digitally controlled, including, but not limited to, the DC offset cancellation loop, the variable gain control loop, and the TIA feedback impedance adjustment loop. The digitally-controlled TIA circuit includes digital loop-control circuitry that consumes less area on the TIA IC chip than the analog circuitry traditionally used to perform the feedback loop control in the analog domain. In addition, because digital logic continues to shrink as IC processes continue to evolve, the size of the IC chip packages will further decrease over time, leading to a smaller footprint in systems in which they are employed. The digital loop control circuitry is also capable of independently varying the gains of multiple gain stages of the variable gain control circuit to provide better control over the gain stages and better overall performance of the TIA circuit.

An avalanche photo-diode (APD) circuit includes a first APD and a bias circuit. The first APD is configured to detect light. The bias circuit is configured to control a gain of the first APD. The bias circuit includes a second APD, a reference voltage source, a bias voltage generation circuit, and a metal layer configured to shield the second APD from the light. The reference voltage source is configured to bias the second APD. The bias voltage generation circuit is configured to generate a bias voltage for biasing the first APD based on dark current output by the second APD.