ADS7056
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ZHCSG66 –MARCH 2017
Typical Applications (continued)
9.2.2.1 Design Requirements
Applications such as ultrasonic flow meters, global positioning systems (GPS), handheld radios, and motor
controls need analog-to-digital converters that are interfaced to high-frequency sensors (200 kHz to 1 MHz). The
goal of the circuit described in Figure 47 is to design a single-supply digital acquisition (DAQ) circuit based on the
ADS7056 with SNR greater than 73 dB and THD less than –85 dB for input frequencies of 200 kHz to 1 MHz at
a throughput of 2.5 MSPS.
9.2.2.2 Detailed Design Procedure
To achieve a SINAD greater than 73 dB, the operational amplifier must have high bandwidth in order to settle the
input signal within the acquisition time of the ADC. The operational amplifier must have low noise to keep the
total system noise below 20% of the input-referred noise of the ADC. For the application circuit shown in
Figure 47, the THS4031 is selected for its high bandwidth (275 MHz), low total harmonic distortion of –90 dB at
1 MHz, and ultra-low noise of 1.6 nV/√Hz. The THS4031 is powered up from dual power supply (VDD = 6 V and
VSS = –6 V).
For chip-select signals, high-frequency system SNR performance is highly dependent on jitter. Thus, selecting a
clock source with very low jitter (< 20-ps RMS) is recommended.
9.2.2.3 Application Curves
Figure 48 shows the FFT plot for the ADS7056 with a 500-kHz input frequency used for the circuit in Figure 47.
Figure 49 shows the FFT plot for the ADS7056 with a 1000-kHz input frequency used for the circuit in Figure 47.
0
0
-50
-50
-100
-150
-200
-100
-150
-200
0
250
500
750
1000
1250
0
250
500
750
1000
1250
Frequency (kHz)
Frequency (kHz)
D035
D038
SNR = 74.2 dB, THD = –90.4 dB, SINAD = 73.5 dB
SNR = 73.5 dB, THD = –87.8 dB, SINAD = 73 dB
Figure 48. Test Results for the ADS7056 and THS4031 for
a 500-kHz Input
Figure 49. Test Results for the ADS7056 and THS4031 for
a 1000-kHz Input
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