An apparatus is described which uses directly modulated InGaN Light-Emitting Diodes (LEDs) or InGaN lasers as the transmitters for an underwater data-communication device. The receiver uses automatic gain control to facilitate performance of the apparatus over a wide-range of distances and water turbidities.

An example optical receiver may have an optical receiver front-end, four slicers, and a logic block. The optical receiver front-end may include a transimpedance amplifier to convert a photodiode output signal to a voltage signal. Three of the slicers may be data slicers, and one of the slicers may be an edge slicer. The slicers may each: shift the voltage signal based on an offset voltage set for the respective slicer, determine whether the shifted voltage signal is greater than a threshold value and generate a number of comparison signals based on the determining, and generate multiple digital signals by demuxing the comparison signals. The logic block may perform PAM-4 to binary decoding based on the data signals output by the data slicers and clock-and-data-recovery based on the digital signals output by the edge slicer.

Embodiments describe a transadmittance amplifier comprising an inverting output port and a non-inverting output port. The transadmittance amplifier comprising a first differential transistor pair having a first transistor comprising an inverting input port. The first transistor is configured to provide an output current to the inverting output port. A second transistor comprising a non-inverting input port. The second transistor is configured to provide an output current to the non-inverting output port. A second differential transistor pair having a third transistor comprising an inverting input port and a fourth transistor comprising a non-inverting input port. A first current source and a second current source. The transadmittance amplifier comprises a first current mirror which is configured to mirror an output current of the fourth transistor to the inverting output port and a second current mirror which is configured to mirror an output current of the third transistor to the non-inverting output port.

Embodiments describe a transadmittance amplifier comprising an inverting output port and a non-inverting output port. The transadmittance amplifier comprising a first differential transistor pair having a first transistor comprising an inverting input port. The first transistor is configured to provide an output current to the inverting output port. A second transistor comprising a non-inverting input port. The second transistor is configured to provide an output current to the non-inverting output port. A second differential transistor pair having a third transistor comprising an inverting input port and a fourth transistor comprising a non-inverting input port. A first current source and a second current source. The transadmittance amplifier comprises a first current mirror which is configured to mirror an output current of the fourth transistor to the inverting output port and a second current mirror which is configured to mirror an output current of the third transistor to the non-inverting output port.

One example of a receiver includes a first stage, a second stage, a third stage, and an automatic gain controller. The first stage amplifies an input signal to provide a first signal. The second stage amplifies or attenuates the first signal to provide a second signal based on a tunable gain of the second stage. The tunable gain is adjusted in response to a differential signal. The third stage amplifies the second signal to provide an output signal. The automatic gain controller provides the differential signal based on a comparison between a peak voltage of the output signal and the sum of a common mode voltage of the output signal and an offset voltage.

A method. The method may include transmitting an optical noise signal to a first photodetector and a second photodetector within an optical receiver circuit that includes a transimpedance amplifier circuit. The method may further include measuring, in response to transmitting the optical noise signal, a power output from the optical receiver circuit. The method may further include determining, using the power output, a difference in photodetector responsivity between the first photodetector and the second photodetector. The method may further include adjusting, using a transimpedance gain controller, an amplifier gain within the optical receiver circuit to decrease a difference in photodetector responsivity between the first photodetector and the second photodetector.

A transimpedance amplifier (TIA) structure includes an input node with a variable inductance component serving to reduce variation in peak amplitude over different gain conditions. According to certain embodiments, an inductor at the TIA input has a first node in communication with a Field Effect Transistor (FET) drain, and a second node in communication with the FET source. A control voltage applied to the FET gate effectively controls the input inductance by adding a variable impedance across the inductor. Under low gain conditions, lowering of inductance afforded by the control voltage applied to the FET reduces voltage peaking. TIAs in accordance with embodiments may be particularly suited to operate over a wide dynamic range to amplify incoming electrical signals received from a photodiode.

Per-port performance optimization may be provided. First, performance data may be received corresponding to each of a plurality of ports. Then it may be determined that performance of at least one of the plurality of ports can be improved based on the received performance data corresponding to the least one of the plurality of ports. Next, in response to determining that the performance of the at least one of the plurality of ports can be improved, at least one of a plurality of components may be adjusted corresponding to the at least one of the plurality of ports to improve performance of the least one of the plurality of ports.

A transimpedance amplifier (TIA) structure includes an input node with a variable inductance component serving to reduce variation in peak amplitude over different gain conditions. According to certain embodiments, an inductor at the TIA input has a first node in communication with a Field Effect Transistor (FET) drain, and a second node in communication with the FET source. A control voltage applied to the FET gate effectively controls the input inductance by adding a variable impedance across the inductor. Under low gain conditions, lowering of inductance afforded by the control voltage applied to the FET reduces voltage peaking. TIAs in accordance with embodiments may be particularly suited to operate over a wide dynamic range to amplify incoming electrical signals received from a photodiode.

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.