Datasheet
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Magnitude (dBv)
0 5 k 10 k 15 k 20 k 25 k 30 k 35 k
Frequency (Hz)
Generator
THS4521
V = 5.0 V
G = 1 V/V
R = 1 k
V = 1 V
S+
F
OUT RMS
W
10-kHz OUTPUT SPECTRUM
THS4521 on AP Analyzer
-50
60
70
80
90
100
110
120
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THD+N (dBv)
0
5
10 15 20
Frequency (kHz)
TOTAL HARMONIC DISTORTION + NOISE
THS4521 Measured on AP Analyzer
THS4521
Signal Generator
-95
97
99
101
103
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105
107
109
111
113
115
THD+N (dB)
10
100
1 k 10 k 100 k
Frequency (Hz)
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY (No Weighting)
THS4521
THS4522
THS4524
www.ti.com
SBOS458F –DECEMBER 2008–REVISED SEPTEMBER 2011
Note that the harmonic distortion performance is very
close to the same with and without the device
meaning the THS4521 performance is actually much
better than can be directly measured by this
meathod. The actual device performance can be
estimated by placing the device in a large noise gain
and using the reduction in loop gain correction. The
THS4521 is placed in a noise gain of 101 by adding a
10-Ω resistor directly across the input terminals of the
circuit shown in Figure 68. This test was performed
using the AP instrument as both the signal source
and the analyzer. The second-order harmonic
distortion at 1 kHz is estimated to be –122 dBc with
V
O
= 1V
RMS
; third-order harmonic distortion is
estimated to be –141 dBc. The third-order harmonic
distortion result matches exactly with design
simulations, but the second-order harmonic distortion
is about 10 dB worse. This result is not unexpected
Figure 70. THS4521 1-V
RMS
10-kHz FFT Plot
because second-order harmonic distortion
performance with a differential signal depends heavily
on cancellation as a result of the differential nature of
The THS4521 shows even better THD+N
the signal, which depends on board layout, bypass
performance when driving higher amplitude output,
capacitors, external cabling, and so forth. Note that
such as 5 V
PP
that is more typical when driving an
the circuit of Figure 68 is also used to measure
ADC. To show performance with an extended
crosstalk between channels.
frequency range, higher gain, and higher amplitude,
the device was tested with 5 V
PP
up to 80 kHz with
the AP. Figure 71 shows the resulting THD+N graph
with no weighting.
Figure 69. THS4521 1-V
RMS
20-Hz
to 20-kHz THD+N
Figure 71. THD+N (No Weighting) on AP, 80-kHz
Bandwidth at G = 1 with 5-V
PP
Output
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