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AD8145YCPZ-R2 Datasheet(PDF) 15 Page - Analog Devices

Part No. AD8145YCPZ-R2
Description  High Speed, Triple Differential Receiver with Comparators
Download  24 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD8145YCPZ-R2 Datasheet(HTML) 15 Page - Analog Devices

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AD8145
Rev. A | Page 15 of 24
APPLICATIONS INFORMATION
OVERVIEW
The AD8145 contains three independent active feedback amplifiers
that can be effectively applied as differential line receivers for
red-green-blue (RGB) signals or component video signals, such
as YPbPr, transmitted over UTP cable. The AD8145 also contains
two general-purpose comparators with hysteresis that can be
used to receive digital signals or to extract video synchronization
pulses from received common-mode signals that contain
encoded synchronization signals.
The comparators, which receive power from the positive supply, are
referenced to GND and require greater than 4.5 V on the positive
supply for proper operation. If the comparators are not used,
then a split ±2.5 V can be used with the amplifiers operating
normally.
The AD8145 includes a power-down feature that can be asserted to
reduce the supply current when a particular device is not in use.
BASIC CLOSED-LOOP GAIN CONFIGURATIONS
Each amplifier in the AD8145 comprises two transconductance
amplifiers—one for the input signal and one for negative feedback.
Note that the closed-loop gain of the amplifier used in the signal
path is defined as the single-ended output voltage of the amplifier
divided by its differential input voltage. Therefore, each amplifier
in the AD8145 provides differential-to-single-ended gain.
Additionally, the amplifier used for feedback has two high
impedance inputs—the feedback input, where the negative
feedback is applied, and the REF input, that can be used as
an independent single-ended input to apply a dc offset to the
output signal.
The AD8145 contains on-chip feedback networks between each
amplifier output and its respective feedback input. The closed-
loop gain of the amplifier is set to 1 by connecting the amplifier
output directly to its respective GAIN_x pin. Doing this places
the on-chip resistors and capacitor in parallel across the amplifier
output and feedback pin. The small feedback capacitor mitigates
the effects of the summing-node capacitance, which is most
problematic in the unity gain case. Closed-loop gain of an
amplifier is set to 2 by connecting the respective GAIN_x pin
to a reference voltage, often directly to ground. In Figure 1,
R = 350 Ω and C = 2 pF.
Some basic gain configurations implemented with an AD8145
amplifier are shown in Figure 33 through Figure 36.
GAIN
REF
R
R
0.01µF
0.01µF
+5V
–5V
C
OUT
VOUT
VIN
VREF
Figure 33. Basic Gain = 1 Circuit: VOUT = VIN + VREF
The gain equation for the circuit in Figure 33 is
VOUT = VIN + VREF
(1)
In this configuration, the voltage applied to the REF pin appears
at the output with a gain of 1.
Figure 34 illustrates one way to operate an AD8145 amplifier
with a gain of 2.
GAIN
REF
R
R
0.01µF
0.01µF
+5V
–5V
C
VREF
VOUT
VIN
Figure 34. Basic Gain = 2 Circuit: VOUT = 2(VIN + VREF)
The gain equation for the circuit in Figure 34 is
VOUT = 2(VIN + VREF)
(2)


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