| Micrel, Inc.'s SY88149HL is a high-sensitivity, burst-mode capable limiting post amplifier designed for optical line terminal (OLT) receiver applications. The SY88149HL satisfies the strict timing restrictions of the GPON standards by providing ultra-fast loss-of-signal (LOS) or signal-detect (SD) output. Auto reset and manual reset options are provided to control LOS/SD output timing. For increased flexibility, this device also includes an option to select between LOS or SD output. The device can be connected to burst-mode capable transimpedance amplifiers (TIAs) using AC or DC coupling.
The SY88149HL generates a high-gain LOS or SD LVTTL output. A programmable LOS/SD level pin (LOS/SD LVL) sets the sensitivity of the input amplitude detection. This device also offers the option to choose between an LOS and SD output from the LOS/SD pin based the LOS/SDSEL pin setting. To select SD output, leave LOS/SDSEL pin open or connect to Vcc; to select LOS output, tie LOS/SDSEL-to-ground. If the input signal amplitude falls below the threshold set by LOS/SD LVL, LOS will assert high (or SD will de-assert low). Once the input signal rises above the threshold set by LOS/SD LVL, LOS will de-assert low (or SD output will assert high). The SY88149HL also features a JAM function, which, when active, disables the LVPECL outputs. JAM is active LOW when SD is selected and active HIGH when LOS is selected. The LOS/SD output should be fed back to the JAM input to maintain output stability under an invalid signal condition. Typically, 3dB SD hysteresis is provided to prevent chattering.
The SY88149HL operates from a single +3.3V power supply over temperatures ranging from -40°C to +85°C. With its wide bandwidth and high gain, signals up to 1.25Gbps and as small as 4mVpp can be amplified to drive devices with LVPECL inputs.