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| THS4121IDGN Datasheet, PDF (10/30 Pages) Texas Instruments – HIGH-SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS | |||
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THS4120
THS4121
SLOS319D â FEBRUARY 2001 â REVISED OCTOBER 2004
APPLICATION INFORMATION
www.ti.com
RESISTOR MATCHING
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
diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or better to
keep the performance optimized.
VOCM sets the dc level of the output signals. If no voltage is applied to the VOCM pin, it is set to the midrail voltage
internally defined as:
ÇVDDÇ ) ÇVSSÇ
2
(1)
In the differential mode, the VOCM on the two outputs cancel each other. Therefore, the output in the differential
mode is the same as the input with the gain of 1. VOCM 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 VOCM pin as a bypass capacitor. The following graph shows the simplified diagram of the THS412x.
VDD
VIN-
VIN+
Vcm Error
Amplifier
+
_
Output Buffer
x1
C
R
C
R
VOUT+
x1
VOUT-
Output Buffer
VDD
30 kâ¦
VSS
30 kâ¦
VSS
VOCM
Figure 18. THS412x Simplified Diagram
10
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