Datasheet
DC-Restore Circuit Comparator
20
Ω
20
Ω
150
Ω
+1
R
2
100k
Ω
V
IN
65
R
2
100
Ω
R
1
40.2
Ω
CCII
B
3
2E
C8
V
OUT
V
REF
C
1
100pF
D
1
D
2
OPA656
The OTA amplifier works as a current conveyor (CCII) in this circuit, with a current gain of 1.
R
1
and C
1
set the DC restoration time constant.
D
1
adds a propogation delay to the DC restoration.
R
2
and C
1
set the decay time constant.
D
1
, D
2
= 1N4148
R
Q
= 1k
Ω
OPA860
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....................................................................................................................................................... SBOS331C – JUNE 2005 – REVISED AUGUST 2008
The OPA860 can be used advantageously with an An interesting and also cost-effective circuit solution
operational amplifier, here the OPA820, as a using the OPA860 as a low-jitter comparator is shown
DC-restore circuit. Figure 56 illustrates this design. in Figure 57 . At the same time, this circuit uses a
Depending on the collector current of the positive and negative feedback. The input is
transconductance amplifier (OTA) of the OPA860, a connected to the inverting E-input. The output signal
switching function is realized with the diodes D
1
and is applied in a direct feedback over the two
D
2
. antiparallel, connected gallium-arsenide diodes back
to the emitter. A second feedback path over the RC
When the C-output is sourcing current, the capacitor
combination to the base, which is a positive
C
1
is being charged. When the C-output is sinking
feedback, accelerates the output voltage change
current, D
1
is turned off and D
2
is turned on, letting
when the input voltage crosses the threshold voltage.
the voltage across C
1
be discharged through R
2
.
The output voltage is limited to the threshold voltage
of the back-to-back diodes.
The condition to charge C
1
is set by the voltage
difference between V
REF
and V
OUT
. For the OTA
C-output to source current, V
REF
has to be greater
than V
OUT
. The rate of charge of C
1
is set by both R
1
and C
1
. The discharge rate is given by R
2
and C
1
.
Figure 56. DC Restorer Circuit
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