THS4271-EP Datasheet, PDF (23/44 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER

THS4271-EP
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SINGLE-SUPPLY OPERATION
The THS4271 is designed to operate from a single
5-V to 15-V power supply. When operating from a
single power supply, care must be taken to ensure
the input signal and amplifier are biased appropriately
to allow for the maximum output voltage swing. The
circuits shown in Figure 78 demonstrate methods to
configure an amplifier in a manner conducive for
single-supply operation.
+V_S
50 Ω Source
V_I
R_T 49.9 Ω
+
THS4271
_
+V_S
2
R_f
R_g
249 Ω
249 Ω
+V_S
2
50 Ω Source
R_g
V_I
249 Ω
61.9 Ω R_T
+V_S
+V_S
2
2
R_f
249 Ω
V_S
_
THS4271
+
V_O
499 Ω
V_O
499 Ω
Figure 78. DC-Coupled Single-Supply Operation
APPLICATION CIRCUITS
Driving an Analog-to-Digital Converter With the
THS4271
The THS4271 can be used to drive high-performance
analog-to-digital converters. Two example circuits are
presented below.
The first circuit uses a wideband transformer to
convert a single-ended input signal into a differential
signal. The differential signal is then amplified and
filtered by two THS4271 amplifiers. This circuit
provides low intermodulation distortion, suppressed
even-order distortion, 14 dB of voltage gain, a 50-Ω
input impedance, and a single-pole filter at 100 MHz.
For applications without signal content at dc, this
method of driving ADCs can be very useful. Where dc
information content is required, the THS4500 family
of fully differential amplifiers may be applicable.
SGLS270C – DECEMBER 2004 – REVISED APRIL 2010
V_CM
50 Ω (1:4 Ω)
Source 1:2
100 Ω
100 Ω
5V
+
THS4271
_
-5 V
249 Ω
24.9 Ω
22 pF
22 pF
249 Ω
ADS5422
14-Bit, 62 Msps
24.9 Ω
V_CM
_
THS4271
+
Figure 79. A Linear, Low-Noise, High-Gain
ADC Preamplifier
The second circuit depicts single-ended ADC drive.
While not recommended for optimum performance
using converters with differential inputs, satisfactory
performance can sometimes be achieved with
single-ended input drive. An example circuit is shown
here for reference.
50 Ω
Source
V_I
49.9 Ω ^RT
+5 V
+
THS4271
_
R_ISO ^{0.1 µF}
16.5 Ω
68 pf
-5 V
R_f
249 Ω
R_g 249 Ω
1.82 kΩ
IN
ADS807
12-Bit,
CM 53 Msps
IN
0.1 µF
For best performance, high-speed ADCs should be driven
differentially. See the THS4500 family of devices for more
information.
Figure 80. Driving an ADC With a
Single-Ended Input
Using the THS4271 as a DAC Output Buffer
Two example circuits are presented here showing the
THS4271 buffering the output of a digital-to-analog
converter. The first circuit performs a differential to
single-ended conversion with the THS4271
configured as a difference amplifier. The difference
amplifier can double as the termination mechanism
for the DAC outputs as well.
Copyright © 2004–2010, Texas Instruments Incorporated
Product Folder Link(s): THS4271-EP
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