ML4622, ML4624
FUNCTIONAL DESCRIPTION
AMPLIFIER
The ML4622, ML4624 have an adjustable Bandwidth
limiting amplifier. Maximum sensitivity is achieved
through the use of a DC restoration feedback loop and
AC coupling the input. When AC coupled, the input DC
bias voltage is set by an on-chip network at about 1.7V.
These coupling capacitors, in conjunction with the input
impedance of the amplifier, establish a high pass filter
with a 3dB corner frequency, f
L
, at
1
f
L
=
2
π
1600C
(1)
The above equation applies when a single capacitor is
tied between CF1 and CF2. When using two capacitors of
equal value (Cap1 from CF1 to V
CC
, Cap2 from CF2 to
V
CC
) the value derived for C should be doubled.
Although the input is AC coupled, the offset voltage
within
the amplifier will be present at the amplifier’s
output. This is represented by V
OS
in figure 2. In order to
reduce this error a DC feedback loop is incorporated. This
negative feedback loop nulls the offset voltage, forcing
V
OS
to be zero. Although the capacitor on V
DC
is non-
V
OUT
+
V
OS
V
OUT
–
Figure 2.
Since the amplifier has a differential input, two capacitors
of equal value are required. If the signal driving the input
is single ended, one of the coupling capacitors can be tied
to V
CC
as shown in figure 1.
CF1 and CF2 create a low pass filter with the corner
frequency determined by the following equation
f
H
=
1
2
π
800 (C + 4pF)
(2)
5pF
+V
RF
CF1
BIAS
0.1
–V
RF
0.01
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FIBER OPTIC CABLE
HFBR
2416
V
IN
–
AMP
ECL
CMP
TTL
CMP
TTL OUT
10Ω
CF2
ECL+
ECL–
2 0.01 V
IN
+
1
4
5
8
0.1
V
DC
CMP ENABLE
3
7
∫
–V
RF
V
REF
REF
V
TH
ADJ
THRESH
GEN
LINK DETECT
TTL LINK MON
V
CC
TTL*
L1
4.7µH
+5V
0.1
+
4.7
L2
4.7µH
+
4.7
0.1
GND
TTL
V
CC
C
TIMER
0.05
+V
RF
GND
–V
RF
*ML4624 ONLY
Note:
If TTL OUT is used, tie GND TTL to unfiltered ground and remove L1. If TTL OUT and ECL outputs are both used, add 3K pulldown resistors at
ECL outputs.
Figure 1. The ML4622, ML4624 Configured for 20MHz Bandwidth
6
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
