sy88289hl Micrel Semiconductor, sy88289hl Datasheet - Page 6

• Manufacturer Part Number: sy88289hl
• Description: Ic Cml Limiting Amp 16mlf
• Manufacturer: Micrel Semiconductor

August 2007
Micrel, Inc.
Functional Block Diagram
Detailed Description
The SY88289HL high-sensitivity limiting post amplifier
operates from a single +3.3V power supply, over
temperatures from –40
rates up to 3.2Gbps and as small as 4mV
amplified. Figure 1 shows the allowed input voltage
swing. The SY88289HL generates a LOS output.
LOS
detection.
Input Amplifier/Buffer
Figure 2 shows a simplified schematic of the
SY88289HL’s input stage. The high-sensitivity of the
input amplifier allows signals as small as 4mV
detected and amplified. The input amplifier also allows
input signals as large as 1800mV
below 6mVpp are linearly amplified with a typical
46dB differential voltage gain. Since it is a limiting
amplifier, the SY88289HL outputs typically 800mV
voltage-limited waveforms for input signals that are
greater than 6mV
SY88289HL to operate with high-gain should have the
upstream TIA placed as close as possible to the
SY88289HL’s
performance of the device.
Output Buffer
The SY88289HL’s CML output buffer is designed to
drive 50Ω lines. The output buffer requires appropriate
termination for proper operation. An external 50
resistor to V
3 shows a simplified schematic of the output stage.
LVL
sets the sensitivity of the input amplitude
CC
for each output pin provides this. Figure
input
PP
. Applications requiring the
o
pins
C to +85
to
o
C. Signals with data
ensure
PP
. Input signals
PP
the
PP
Ω
can be
to be
best
PP
6
Loss-of-Signal
The SY88289HL generates a chatter-free LOS open-
collector TTL output with an internal 4.75k
resistor, as shown in Figure 4. LOS is used to
determine that the input amplitude is large enough to
be considered a valid input. LOS asserts high if the
input amplitude falls below the threshold sets by
LOS
back to the enable bar (/EN) input to maintain output
stability under a loss of signal condition. /EN de-
asserts the true output signal without removing the
input signals. Typically, 3.5dB LOS hysteresis is
provided to prevent chattering.
Loss-of-Signal Level Set
A programmable LOS level-set pin (LOS
threshold of the input amplitude detection. Connecting
an external resistor between V
voltage at LOS
V
between V
Hysteresis
The SY88289HL typically provides 3.5dB LOS
electrical hysteresis. By definition, a power ratio
measured in dB is 10log (power ratio). Power is
calculated as V
the same ratio can be stated as 20log (voltage ratio).
While in linear mode, the electrical voltage input
changes linearly with the optical power and therefore,
the ratios change linearly. Thus, the optical hysteresis
in dB is half the electrical hysteresis in dB given in the
data sheet. Since the SY88289HL is an electrical
device, this data sheet refers to hysteresis in electrical
terms. With 3.5dB LOS hysteresis, a voltage factor of
1.5 is required to assert or de-assert LOS.
REF
LVL
. The external resistor creates a voltage divider
and de-asserts low otherwise. LOS can be fed
CC
and V
LVL
2
IN
[e-mail]
. This voltage ranges from V
/R for an electrical signal. Hence,
REF
, as shown in Figure 5.
CC
and LOS
or [phone]
M9999-082007-A
Ω pull
SY88289HL
LVL
LVL
) sets the
sets the
CC
-up
to