THS4521 datasheet(29/48 Pages) TI

29 / 48 page

100

110

120

130

140

5 k

10 k

15 k

20 k

25 k

30 k

35 k

Frequency (Hz)

Generator

THS4521

= 5.0 V

G = 1 V/V

R = 1 k

= 1 V

S+

OUT

RMS

10-kHz OUTPUT SPECTRUM

THS4521 on AP Analyzer

100

110

120

Frequency (kHz)

TOTAL HARMONIC DISTORTION + NOISE

THS4521 Measured on AP Analyzer

THS4521

Signal Generator

101

103

105

107

109

111

113

115

100

1 k

10 k

100 k

Frequency (Hz)

TOTAL HARMONIC DISTORTION + NOISE

vs FREQUENCY (No Weighting)

THS4521

THS4522

THS4524

www.ti.com

SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010

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

directly

measured

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

VO = 1VRMS; 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-VRMS 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 VPP 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 VPP up to 80 kHz with

the AP. Figure 71 shows the resulting THD+N graph

with no weighting.

Figure 69. THS4521 1-VRMS 20-Hz

to 20-kHz THD+N

Figure 71. THD+N (No Weighting) on AP, 80-kHz

Bandwidth at G = 1 with 5-VPP Output

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