AD7863ARSZ-3 Analog Devices Inc, AD7863ARSZ-3 Datasheet - Page 14

• Manufacturer Part Number: AD7863ARSZ-3
• Description: IC,Data Acquisition System,2-CHANNEL,14-BIT,SSOP,28PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD7863ARSZ-3

• Number Of Bits: 14
• Sampling Rate (per Second): 175k
• Data Interface: Parallel
• Number Of Converters: 2
• Power Dissipation (max): 94.5mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7863
AD7863 DYNAMIC SPECIFICATIONS
The AD7863 is specified and tested for dynamic performance as
well as traditional dc specifications such as integral and
differential nonlinearity. These ac specifications are required for
the signal processing applications such as phased array sonar,
adaptive filters, and spectrum analysis. These applications
require information on the ADC’s effect on the spectral content
of the input signal. Hence, the parameters for which the
AD7863 is specified include SNR, harmonic distortion,
intermodulation distortion, and peak harmonics. These terms
are discussed in more detail in the following sections.
SIGNAL-TO-NOISE RATIO (SNR)
SNR is the measured signal-to-noise ratio at the output of the
ADC. The signal is the rms magnitude of the fundamental.
Noise is the rms sum of all the nonfundamental signals up to
half the sampling frequency (f
dependent upon the number of quantization levels used in the
digitization process; the more levels, the smaller the
quantization noise. The theoretical signal-to-noise ratio for a
sine wave input is given by
where N is the number of bits.
Thus for an ideal 14-bit converter, SNR = 86.04 dB.
Figure 12 shows a histogram plot for 8192 conversions of a dc
input using the AD7863 with 5 V supply. The analog input was
set at the center of a code transition. It can be seen that the
codes appear mainly in the one output bin, indicating very good
noise performance from the ADC.
The output spectrum from the ADC is evaluated by applying
a sine wave signal of very low distortion to the V
which is sampled at a 175 kHz sampling rate. A fast fourier
transform (FFT) plot is generated from which the SNR data can
be obtained. Figure 13 shows a typical 8192 point FFT plot of
the AD7863 with an input signal of 10 kHz and a sampling
SNR = (6.02N + 1.76) dB
8000
7000
6000
5000
4000
3000
2000
1000
Figure 12. Histogram of 8192 Conversions of a DC Input
0
746
747
748
749
S
/2), excluding dc; SNR is
750
CODE
751
752
753
AX/BX
754
input,
755
Rev. B | Page 14 of 24
(1)
frequency of 175 kHz. The SNR obtained from this graph is
−80.72 dB. It should be noted that the harmonics are taken into
account when calculating the SNR.
EFFECTIVE NUMBER OF BITS
The formula given in Equation 1 relates the SNR to the number
of bits. Rewriting the formula, as in Equation 2, it is possible to
obtain a measure of performance expressed in effective number
of bits (N).
The effective number of bits for a device can be calculated
directly from its measured SNR.
Figure 14 shows a typical plot of effective numbers of bits vs.
frequency for an AD7863-2 with a sampling frequency of
175 kHz. The effective number of bits typically falls between
13.11 and 11.05 corresponding to SNR figures of 80.68 dB
and 68.28 dB.
N
–100
–110
–120
–130
–140
–150
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
–10
–20
–30
–40
–50
–60
–70
–80
–90
=
0
SNR
0
0
Figure 14. Effective Numbers of Bits vs. Frequency
. 6
−
02
10
. 1
76
200
20
Figure 13. AD7863 FFT Plot
30
FREQUENCY (kHz)
FREQUENCY (kHz)
400
40
50
600
f
60
f
SNR = +80.72dB
THD = –92.96dB
SAMPLE
IN
= 10kHz
70
800
= 175kHz
80
1000
90
(2)