| Micrel, Inc.'s SY88053AL limiting post amplifier is designed for use in fiber-optic receivers for applications up to 12.5Gbps. It features a decision threshold control that can be used for offset compensation or to optimize the bit error rate (BER) in noisy applications such as WDM where optical amplifiers like EDFAs and Raman amplifiers are used. This device connects to typical transimpedance amplifiers (TIAs). The signal from a TIA can contain significant amounts of noise unevenly distributed between its top and bottom rails due to the amplified spontaneous emission (ASE) noise generated by the optical amplifiers. In order to optimize the BER in such noisy conditions, the decision threshold between bit I and bit 0 needs to be moved to the rail that contains less noise. An external voltage applied at the VTHP pin on the SY88053AL will move the crossing point up and down, from 20 to 80 percent to achieve the best BER.
The SY88053AL operates from a single +3.3V power supply over temperatures ranging from -40°C to +85°C. It can detect and amplify signals up to 12.5Gbps and amplitude as low as 15mVPP.
The SY88053AL generates a loss-of-signal (LOS) open-collector TTL output. A programmable SOS level set pin (LOSLVL) sets the sensitivity of the input amplitude detection. LOS asserts high if the input amplitude falls below the threshold set by LOSLVL and de-asserts low otherwise. The enable input (lEN) de-asserts the true output signal without removing the input signal. The LOS output can be fed back to the /EN input to implement the squelch function that maintains output stability under a loss-of-signal condition.