SY88843VKI Micrel Inc, SY88843VKI Datasheet - Page 7

• Manufacturer Part Number: SY88843VKI
• Description: IC AMP LIMIT CML TTL SD 10MSOP
• Manufacturer: Micrel Inc
• Type: Limiting Postamplifierr

Specifications of SY88843VKI

• Applications: Optical Networks
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Micrel, Inc.
from a single +3.3V 10% or +5V 10% power supply, over
an industrial temperature range of –40 C to +85 C. Signals
with data rates up to 3.2Gbps and as small as 10mV
be amplified. Figure 1 shows the allowed input voltage swing.
The SY88843V generates an SD output, providing feedback
to EN for output stability. SDLVL sets the sensitivity of the
input amplitude detection.
Input Amplifier/Buffer
to REF. Unless unaffected by this internal termination
scheme, upstream devices need to be AC-coupled to the
SY88843V’s inputs. Figure 2 shows a simplified schematic
of the input structure.
amplifies as small as 10mV
input signals as large as 1800mV
amplified with a typically 38dB differential voltage gain. Since
it is a limiting amplifier, the SY88843V outputs typically
800mV
are greater than 10mV
SY88843V to operate with high gain should have the
upstream TIA placed as close as possible to the SY88843V’s
input pins to ensure the device's best performance of the
device.
Output Buffer
50 lines. The output buffer requires appropriate termination
for proper operation. An external 50
equivalent for each output pin provides 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
for external termination. As noted in the previous section,
the amplifier outputs, typically 800mV
25
16mA tail-current. Figure 4 shows the power supply current
measurement which excludes the 16mA tail-current.
Signal Detect
collector TTL output with internal 4.75k
shown in Figure 5. SD is used to determine that the input
amplitude large enough to be considered a valid input. SD
asserts high if the input amplitude rises above the threshold
set by SDLVL and de-asserts low otherwise. SD 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 SD hysteresis is provided to prevent chattering.
M9999-110905
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DETAILED DESCRIPTION
The SY88843V low-power, limiting post amplifier operates
The SY88843V’s inputs are internally terminated with 50
The high sensitivity of the input amplifier detects and
The SY88843V’s CML output buffer is designed to drive
The SY88843V incorporates a chatter-free, SD open-
total loads. The output buffer, thus, switches typically
PP
voltage-limited waveforms for input signals that
PP
. Applications requiring the
PP
. The input amplifier allows
to VCC eliminates the need
PP
. Input signals are linearly
PP
, waveforms across
resistor to VCC or
pull-up resistor as
PP
can
7
Signal Detect-Level Set
threshold of the input amplitude detection. Connecting an
external resistor between VCC and SDLVL sets the voltage
at SDLVL. This voltage ranges from V
external resistor creates a voltage divider between V
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 SDLVL to VCC, the lower the SD
sensitivity. Hence, larger input amplitude is required to assert
SD. 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
the ratios change linearly. Therefore, the optical hysteresis
in dB is half the electrical hysteresis in dB given in the
datasheet. The SY88843V provides typically 2.3dB SD
optical hysteresis. As the SY88843V is an electrical device,
this datasheet refers to hysteresis in electrical terms. With
4.6dB SD hysteresis, a voltage factor of 1.7 is required to
assert SD.
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, signal-detect level set pin sets the
The smaller the external resistor, which implies a smaller
The SY88843V provides typically 4.6dB SD electrical
If increased SD sensitivity and hysteresis are required,
V
SDLVL
V
CC
–
1 3
R
SDLVL
SDLVL
R
SDLVL
SDLVL
+
2 8
and R
or R
SDLVL
SDLVL
is given by:
CC
.
to V
2
IN
SY88843V
/R for an
REF
CC
. The
and