The SY88903AL, burst mode, high-sensitivity limiting post amplifier is designed for use in fiber-optic receivers, specially optimized for passive optical networks (PONs). The device connects to typical transimpedance amplifiers (TIAs). The linear signal output from TIAs can contain significant amounts of noise and may vary in amplitude over time. The SY88903AL quantizes these signals and outputs PECL level waveforms.
The SY88903AL operates from a single +3.3V power supply, over temperatures ranging from -40°C to +85°C. Signals with data rates from 622Mbps up to 1.25Gbps, and as small as 5mVPP, can be amplified to drive devices with PECL inputs.
The SY88903AL generates a Loss-of-Signal (LOS) open-collector TTL output. A programmable Loss-of-Signal level set pin (LOS LVL) sets the sensitivity of the input amplitude detection. LOS asserts high if the input amplitude falls below the threshold set by LOS LVL and de-asserts low otherwise. The enable bar input (/EN) de-asserts the true output signal without removing the input signal. The LOS output can be fed back to the /EN input to maintain output stability under a loss-of-signal condition. Typically, 3.4dB LOS hysteresis is provided to prevent chattering.
The SY88903 limiting post amplifier with its high gain and wide bandwidth is ideal for use as a post amplifier in fiber-optic receivers with data rates up to 1.25Gbps. Signals as small as 5mVp-p can be amplified to drive devices with PECL inputs. The SY88903 generates a chatter-free Loss of Signal (LOS) open collector TTL output. The SY88903 incorporates a programmble level detect function to identify when the input signal has been lost. This information can be fed back to the /EN input of the device to maintain stability under loss of signal conditions. Using LOSLVL pin the sensitivity of the level detect can be adjusted. The LOS LVL voltage can be set by connecting a resistor divider between VCC and VREF, Figure 3. Figure 4 shows the relationship between input level sensitivity and the voltage set on LOSLVL. Figure 5 shows the relationship between input level sensitivity and resistor divider ratio. The LOS output is a TTL open collector output that requires pull-up resistor for proper operation, Figure 1. +5V 2k SY88903 LOS Figure 1. LOS Output with Desired Rise Time DOUT ECL Buffer DOUT Enable Level Detect EN