SY88773VKG Micrel Inc, SY88773VKG Datasheet - Page 7

• Manufacturer Part Number: SY88773VKG
• Description: IC AMP LIMIT CML TTL LOS 10MSOP
• Manufacturer: Micrel Inc
• Type: Limiting Postamplifierr

Specifications of SY88773VKG

• Applications: Optical Networks
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-1408

Micrel, Inc.
from a single +3.3V or +5V power supply, over temperatures
from –40 C to +85 C. Signals with data rates up to 3.2Gbps
and as small as 10mV
the allowed input voltage swing. The SY88773V generates
an LOS output, providing feedback to /EN for output stability.
LOSLVL sets the sensitivity of the input amplitude detection.
Input Amplifier/Buffer
DC bias point. If AC-coupling to the SY88773V, REF can
be used as the DC bias point by externally connecting the
inputs through appropriate termination resistors to REF. If
DC-coupling to the SY88773V, ensure the upstream device’s
output swing meets the SY88773V’s common mode range.
Figure 2 shows a simplified schematic of the input structure.
amplifies signals as small as 10mV
allows input signals as large as 1800mV
are linearly amplified with a typically 38dB differential voltage
gain. Since it is a limiting amplifier, the SY88773V outputs
typically 800mV
that are greater than 10mV
SY88773V to operate with high-gain should have the
upstream TIA placed as close as possible to the SY88773V’s
input pins to ensure the device’s best performance.
Output Buffer
50 lines. The output buffer requires appropriate termination
for proper operation. An external 50
equivalent for each output pin provides appropriate output
buffer termination. Figure 3 shows a simplified schematic of
the output structure and includes an appropriate termination
method. Of course, driving a downstream device with a
CML input that is internally terminated with 50
eliminates the need for external termination. As noted in
the previous section, the amplifier outputs, typically 800mV
waveforms across 25
switches typically 16mA tail-current. Figure 4 shows the
power supply current measurement which excludes the
16mA tail-current.
Loss-of-Signal
collector TTL output with internal 4.75k
shown in Figure 5. LOS is used to determine that the input
amplitude is too small to be considered a valid input. LOS
M9999-110905
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DETAILED DESCRIPTION
The SY88773V low-power, limiting post amplifier operates
The SY88773V input is designed for V
The high-sensitivity of the input amplifier detects and
The SY88773V’s CML output buffer is designed to drive
The SY88773V incorporates a chatter-free, LOS open-
pp
voltage-limited waveforms for input signals
pp
total loads. The output buffer, thus,
can be amplified. Figure 1 shows
pp
. Applications requiring the
pp
. The input amplifier
resistor to VCC or
REF
pull-up resistor as
pp
. Input signals
as its nominal
to VCC
pp
,
7
asserts high if the input amplitude falls below the threshold
set by LOSLVL and de-asserts low otherwise. LOS can be
fed back to the enable (/EN) input to maintain output stability
under a loss-of-signal condition. /EN de-asserts low the
true output signal without removing the input signals.
Typically, 4.6dB LOS hysteresis is provided to prevent
chattering.
Loss-of-Signal Level Set
threshold of the input amplitude detection. Connecting an
external resistor between VCC and LOSLVL sets the voltage
at LOSLVL. This voltage ranges from V
external resistor creates a voltage divider between VCC
and REF as shown in Figure 6. If desired, an appropriate
external voltage may be applied rather than using a resistor.
The relationship between V
where voltages are in volts and resistances are in k .
voltage difference from LOSLVL to VCC, the lower the LOS
sensitivity. Hence, larger input amplitude is required to de-
assert LOS. The “Typical Operating Characteristics” section
contains graphs showing the relationship between the input
amplitude detection sensitivity and V
Hysteresis
hysteresis. By definition, a power ratio measured in dB is
10log(power ratio). Power is calculated as V
electrical signal. Hence, 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,
hence, the ratios change linearly. Therefore, the optical
hysteresis in dB is half the electrical hysteresis in dB given
in the datasheet. The SY88773V provides typically 2.3dB
LOS optical hysteresis. As the SY88773V is an electrical
device, this datasheet refers to hysteresis in electrical terms.
With 4.6dB LOS hysteresis, a voltage factor of 1.7 is required
to de-assert LOS.
Hysteresis and Sensitivity Improvement
an application note entitled “Notes on Sensitivity and
Hysteresis in Micrel Post Amplifiers” is available at http://
www.micrel.com/product-info/app_hints+notes.shtml.
A programmable, loss-of-signal level set pin sets the
The smaller the external resistor, which implies a smaller
The SY88773V provides typically 4.6dB LOS electrical
If increased LOS sensitivity and hysteresis are required,
V
LOSLVL
V
CC
–
1 3
.
R
LOSLVL
R
LOSLVL
LOSLVL
+
2 8
.
and R
LOSLVL
LOSLVL
CC
or R
to V
2
IN
is given by:
LOSLVL
SY88773V
/R for an
REF
. The
.