In optical module products, realizing photoelectric conversion is one of the basic functions of optical modules. Since the received optical signal is a very weak current signal and needs to be converted into a voltage signal through an analog circuit, the mainstream solution is to use an operational amplifier to design. Then the response time, bandwidth, signal-to-noise ratio and other characteristics of the operational amplifier IC have become the focus of attention when converting optical signals into electrical signals. And what we recommend today is SGMICRO's operational amplifier SGM8541XN5/TR using low-noise CMOS technology, its amplification bandwidth is 1.1Mhz, and the rail-to-rail output with only 0.8mv voltage drop is completely suitable for optical module communication. Compared with the operational amplifiers of companies such as Maxim and ADI in the same industry, pin-pin compatible replacement can be achieved, and the BOM cost of the optical module can be reduced at the same time.

The block diagram of the optical module includes two parts: the transmitting end and the receiving end. The transmitting end includes the optical signal transmission circuit, the CDR clock data recovery circuit, the temperature control circuit and the control circuit, using the input equalizer, multi-rate CDR, EML (electro-absorption modulated laser) The driver and APC integrated chip-driven laser realizes electrical/optical conversion. The receiving end includes a light receiving circuit and an MCU control circuit. The front end uses APD (Avalanche Photodiode) to convert the detected optical signal into an electrical signal, and then amplifies and reshapes it through the op amp SGM8541XN5/TR and outputs it to the MCU. Take ADC sampling.

At the optical receiving end, in order to meet the requirement that the optical signal can be detected when it reaches 0.1%, it is required that the operational amplifier SGM8541XN5/TR can detect 0.1% of the optical signal within 5.3us under the condition of G=G+1.2. light signal. At the same time, when the operational amplifier gain exceeds the set value, the operational amplifier SGM8541XN5/TR will complete the self-recovery function within 2.6us.

Since the current signal at the receiving end is not allowed to introduce other interference signal sources when converting the voltage signal, it is required that the designed circuit has a high signal-to-noise ratio and ripple interference capability, and has the function of temperature compensation. Under the condition of f = 10kHz, the voltage-to-noise ratio of the operational amplifier SGM8541XN5/TR is 20nv/hz, and the operational amplifier SGM8541XN5/TR has its own function of input voltage compensation coefficient of 2.7uv/℃, which completely solves the problem of the optical module due to long-term problems. Using, the signal is disturbed by the technical problem of drifting.

At present, Shengbang Micro's operational amplifier SGM8541XN5/TR has been adopted by some optical module companies. From the actual test waveform, the output of the operational amplifier SGM8541XN5/TR can completely accept the current signal output by the front-end APD, and when the voltage waveform is relatively high When it is large, the output waveform of the operational amplifier SGM8541XN5/TR does not interfere greatly with it. Explain that the operational amplifier SGM8541XN5/TR can be used in optical module communication products.