THS4551 Datasheet, PDF (42/70 Pages) Texas Instruments – Low-Noise, Precision, 150-MHz, Fully Differential Amplifier

THS4551
SBOS778A – APRIL 2016 – REVISED AUGUST 2016
www.ti.com
10.1.4 Interfacing to High-Performance Precision ADCs
The THS4551 provides a simple interface to a wide variety of precision SAR and delta-sigma (ΔΣ) ADCs. To
deliver the exceptional distortion at the output pins, considerably wider bandwidth than what is typically required
in the signal path to the ADC inputs is provided by the THS4551. This wide amplifier bandwidth provides the low
broadband, closed-loop output impedance to supply the sampling glitches and to recover quickly for the best
SFDR. A particularly challenging task is to drive the high-frequency modulator sample rates for a precision ΔΣ
converter where the modulator frequency can be far higher than the final output data rate. Figure 78 shows a
tested example circuit using the THS4551 in a 500-kHz, active multiple feedback (MFB) filter driving the 24-bit
ADS127L01. This filter is designed for F_O = 500 kHz and Q = 0.63 to give a linear phase response with the –3-
dB frequency at 443 kHz.
1.2 k
270 pF
1.2 k
470 pF
1.2 k
330
1 nF
330
3V
+
±
5
THS4551
5
10
22 nF
AINN
ADS127L01
AINP
10
270 pF
1.2 k
Copyright © 2016, Texas Instruments Incorporated
Figure 78. 500-kHz Low-Pass Active Filter
This 3-V supply example provides a low-power interface to the very low-power ADC. This circuit is available on
the ADS127L01EVM board.
The 5-Ω resistors inside the loop at the output pins and the 1-nF differential capacitor across the FDA input pins
are not part of the filter design. These elements function to improve the loop-phase margin with minimal
interaction with the active filter operation. Tested performance with the ADS127L01 at a 4-kHz input shows the
exceptional THD and SNR of –114 dBc and 106 dB, respectively. Figure 79 uses the ADS127L01 at a modulator
frequency of 16 MHz.
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
0
20
40
60
80
100 120
Frequency (kHz)
D066
Figure 79. 4-kHz FFT Test for the Gain of 1 V/V Interface in Figure 78
42
Submit Documentation Feedback
Product Folder Links: THS4551
Copyright © 2016, Texas Instruments Incorporated