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PDF ( 数据手册 , 数据表 ) MAX3762

零件编号 MAX3762
描述 622Mbps Limiting Amplifiers
制造商 Maxim Integrated
LOGO Maxim Integrated LOGO 


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MAX3762 数据手册, 描述, 功能
19-1097; Rev 4; 8/08
EVAALVUAAILTAIOBNLEKIT
Low-Power, 622Mbps Limiting Amplifiers
with Chatter-Free Power Detect for LANs
_______________General Description
The MAX3761/MAX3762 limiting amplifiers, with 4mV
sensitivity and PECL data outputs, are optimized for
operation in low-cost, 622Mbps, LAN/ATM LAN fiber
optics applications.
An integrated power detector senses the input signal’s
amplitude. A received-signal-strength indicator (RSSI)
gives an analog indication of the power level, while the
complementary loss-of-signal (LOS) outputs indicate if
the input power level exceeds the programmed
threshold level. The LOS threshold can be adjusted to
detect signal amplitudes between 3mVp-p and
100mVp-p, providing a 15dB LOS adjustment in fiber
optic receivers. The LOS outputs have 3.5dB of
hysteresis, which prevents chatter when input signal
levels are small. The MAX3761’s LOS outputs are com-
patible with TTL-logic levels. The MAX3762 has PECL
LOS outputs.
DISABLE and LOS can be used to implement a squelch
function, which turns off the data outputs when the
input signal is below the programmed threshold.
________________________Applications
622Mbps LAN/ATM LAN Receivers
155Mbps LAN/ATM LAN Receivers
____________________________Features
Chatter-Free Power Detector with Programmable
Loss-of-Signal Outputs
4mV Input Sensitivity
PECL Data Outputs
Single 5V Power Supply
250ps Output Edge Speed
Low 15ps Pulse-Width Distortion
TTL Loss-of-Signal Interface Logic—MAX3761
PECL Loss-of-Signal Interface Logic—MAX3762
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX3761EEP+
-40°C to +85°C 20 QSOP
MAX3761E/D
-40°C to +85°C Dice*
MAX3762EEP+
-40°C to +85°C 20 QSOP
MAX3762E/D
-40°C to +85°C Dice*
*Dice are designed to operate from -40°C to +85°C, but are
tested and guaranteed only at TA = +25°C.
+Denotes a lead-free/RoHS-compliant package.
__________________Pin Configuration _________Typical Operating Circuits
TOP VIEW
FILTER 1
RSSI 2
EN 3
VCC 4
VIN+ 5
VIN- 6
GND 7
SUB 8
CZP 9
CZN 10
MAX3761
MAX3762
20 DISABLE
19 LOS+
18 LOS-
17 VCC
16 VCCO
15 OUT+
14 OUT-
13 GNDO
12 VTH
11 INV
QSOP
+5V
100pF
BYPASS
SUPPLY
10nF
CIN
5.6nF
CIN
5.6nF
100pF
CFILTER
+VCC
VCC
EN
RSSI
VCCO
VIN+
CZP
CZN
DISABLE
LOS+
LOS-
OUT-
OUT+
MAX3761
VIN- GNDO
FILTER
GND
INV VTHSUB
CAZ
150pF
50Ω
50Ω
VCC - 2V
R1
100kΩ
R2
22kΩ
MAX3762 at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
http://www.Datasheet4U.com







MAX3762 pdf, 数据表
Low-Power, 622Mbps Limiting Amplifiers
with Chatter-Free Power Detect for LANs
Capacitor Selection
A typical MAX3761/MAX3762 implementation requires
four external capacitors. To select the capacitors, first
determine the following parameters in the receiver sys-
tem (see the Applications Information section for rec-
ommendations in 622Mbps ATM and Fibre Channel
1063Mbps systems):
1) The duration of the expected longest run of consec-
utive bits in the data stream. For example, 72 con-
secutive zeros in a 622Mbps data stream have a
duration of 116ns.
2) The maximum allowable data-dependent jitter.
3) The desired power-detector integration time con-
stant [1 / (2πfINT)].
4) The transimpedance amplifier’s maximum peak-to-
peak output voltage.
Step 1. Select the Input AC-Coupling Capacitors (CIN).
When using a limiting preamplifier with a highpass
frequency response, select CIN to provide a low-
frequency cutoff (fC) one decade lower than the
preamplifier low-frequency cutoff. This causes nearly all
data-dependent jitter (DDJ) to be generated in the pre-
amplifer circuit. For example, if the preamplifier’s low-
frequency cutoff is 150kHz, then select CIN to provide a
15kHz low-frequency cutoff.
Select CIN with the following equation:
CIN
=
1
2πfC1950Ω
For differential input signals, use a capacitor equal to
CIN on both inputs (VIN+ and VIN-). For single-ended
input signals, one capacitor should be tied to VIN+ and
another should decouple VIN- to ground.
When using a preamplifier without a highpass
response, select CIN to ensure that data-dependent jit-
ter is acceptable. The following equation provides an
estimate for CIN:
CIN
-tL
1950ln
1
⎣⎢
(DDJ)(BW)
0.5
⎦⎥
where: tL = duration of the longest run of consecutive
bits with the same value (seconds); DDJ = maximum
allowable data-dependent jitter, peak-to-peak (seconds);
BW = typical system bandwidth, normally 0.6 to 1.0
times the data rate (hertz).
Regardless of which method is used to select CIN, the
maximum LOS assert time can be estimated from the
value of CIN. The following equation estimates LOS time
delay when the maximum-amplitude signal is instanta-
neously removed from the input, and when the FILTER
time constant is much faster than the input time con-
stant (CFILTER < 0.4CIN):
tLOS ASSERT = 1950CINln(VMAXp-p / VASSERTp-p)
where VMAXp-p is the maximum output of the preampli-
fier, and VASSERTp-p is the input amplitude that causes
LOS to assert. The equation describes the input capac-
itors’ discharge time, from maximum input to the LOS
threshold into the 1950Ω, single-ended input resis-
tance.
Step 2. Select the Offset-Correction Capacitor (CAZ).
To maintain stability, it is important to keep a one-
decade separation between fC and the low-frequency
cutoff associated with the DC-offset-correction circuit
(fOC).
The input impedance between CZP and CZN is
approximately 800kΩ in parallel with 10pF. As a result,
the low-frequency cutoff (fOC) associated with the DC-
offset-correction loop is computed as follows:
( )fOC = 2π800kΩ
1
C AZ + 10pF
where CAZ is an optional external capacitor between
CZP and CZN.
If CIN is known, then:
C AZ
CIN
41
10pF
Step 3. Select the Power-Detect Integration Capacitor
(CFILTER). For 622Mbps ATM applications, Maxim rec-
ommends a filter frequency of 3MHz, which requires
CFILTER = 100pF. The integration frequency can be
selected lower to remove low-frequency noise, or to
prevent unusual data sequences from asserting LOS.
CFILTER = 1 / ( 2π500fINT)
where fINT is the integration frequency.
8 _______________________________________________________________________________________
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