Datasheet

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APPLICATION INFORMATION
RESISTOR MATCHING
ǒ
V
CC)
Ǔ
)
ǒ
V
CC–
Ǔ
2
_
+
x1
Output Buffer
Vcm Error
Amplifier
C R
C
R
x1
Output Buffer
V
OUT+
V
OUT-
V
CC+
V
CC-
V
IN-
V
IN+
30 kΩ
30 kΩ
V
CC+
V
CC-
V
OCM
THS4140
THS4141
SLOS320F – MAY 2000 – REVISED JANUARY 2006
Resistor matching is important in fully differential amplifiers. The balance of the output on the reference voltage
depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the second harmonic distortion
will diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or better to
keep the performance optimized.
V
OCM
sets the dc level of the output signals. If no voltage is applied to the V
OCM
pin, it will be set to the midrail
voltage internally defined as:
In the differential mode, the V
OCM
on the two outputs cancel each other. Therefore, the output in the differential
mode is the same as the input in the gain of 1. V
OCM
has a high bandwidth capability up to the typical operation
range of the amplifier. For the prevention of noise going through the device, use a 0.1 µF capacitor on the V
OCM
pin as a bypass capacitor. Figure 21 shows the simplified diagram of the THS414x.
Figure 21. THS414x Simplified Diagram
11
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