THS4211 Datasheet, PDF (22/41 Pages) Texas Instruments – LOW-DISTORTION HIGH-SPEED VOLTAGE FEEDBACK AMPLIFIER

THS4211
THS4215
SLOS400D – SEPTEMBER 2002 – REVISED NOVEMBER 2004
V_CM
50 Ω (1:4 Ω)
Source 1:2
196 Ω
196 Ω
5V
+
THS4211
_
-5 V
392 Ω
24.9 Ω
15 pF
15 pF
392 Ω
ADS5422
14-Bit, 62 Msps
24.9 Ω
V_CM
_
THS4211
+
Figure 78. 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
+
THS4211
_
R_ISO ^{0.1 µF}
16.5 Ω
68 pf
-5 V
R_f
392 Ω
R_g 392 Ω
1.82 kΩ
IN
ADS807
12-Bit,
CM 53 Msps
IN
0.1 µF
NOTE: For best performance, high-speed ADCs should be driven
differentially. See the THS4500 family of devices for more
information.
Figure 79. Driving an ADC With a
Single-Ended Input
Using the THS4211 as a DAC Output Buffer
Two example circuits are presented here showing the
THS4211 buffering the output of a digital-to-analog
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converter. The first circuit performs a differential to
single-ended conversion with the THS4211 con-
figured as a difference amplifier. The difference
amplifier can double as the termination mechanism
for the DAC outputs as well.
3.3 V 3.3 V
100 Ω
100 Ω
DAC5675
14-Bit,
400 MSps
392 Ω
196 Ω
392 Ω
392 Ω
+5 V
_
THS4211
+
-5 V
392 Ω
49.9 Ω
RF
LO
Figure 80. Differential to Single-Ended
Conversion of a High-Speed DAC Output
For cases where a differential signaling path is
desirable, a pair of THS4211 amplifiers can be used
as output buffers. The circuit depicts differential drive
into a mixer's IF inputs, coupled with additional signal
gain and filtering.
3.3 V 3.3 V
100 Ω
100 Ω
1 nF
THS4211
+
_
C_F
DAC5675
14-Bit,
400 MSps
392 Ω
100 Ω
392 Ω
392 Ω
392 Ω
1 nF
_
C_F
1 nF
IF+
49.9 Ω
49.9 Ω
RF_(out)
IF-
1 nF
+
THS4211
Figure 81. Differential Mixer Drive Circuit
Using the DAC5675 and the THS4211
Active Filtering With the THS4211
High-frequency active filtering with the THS4211 is
achievable due to the amplifier's high slew-rate, wide
bandwidth, and voltage feedback architecture. Sev-
eral options are available for high-pass, low-pass,
bandpass, and bandstop filters of varying orders. A
simple two-pole low pass filter is presented here as
an example, with two poles at 100 MHz.
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