AD7710 데이터 시트보기 (PDF) - Analog Devices
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AD7710 Datasheet PDF : 32 Pages
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AD7710
Tables I and II show the output rms noise for some typical
notch and –3 dB frequencies. The numbers given are for the
bipolar input ranges with a VREF of 2.5 V. These numbers are
typical and are generated with an analog input voltage of 0 V.
The output noise from the part comes from two sources. First,
there is the electrical noise in the semiconductor devices used in
the implementation of the modulator (device noise). Second,
when the analog input signal is converted into the digital do-
main, quantization noise is added. The device noise is at a low
level and is largely independent of frequency. The quantization
noise starts at an even lower level but rises rapidly with increas-
ing frequency to become the dominant noise source. Conse-
quently, lower filter notch settings (below 60 Hz approximately)
tend to be device-noise dominated while higher notch settings
are dominated by quantization noise. Changing the filter notch
and cutoff frequency in the quantization noise dominated region
results in a more dramatic improvement in noise performance
than it does in the device noise dominated region as shown in
Table I. Furthermore, quantization noise is added after the PGA,
so effective resolution is independent of gain for the higher filter
notch frequencies. Meanwhile, device noise is added in the PGA
and, therefore, effective resolution suffers a little at high gains
for lower notch frequencies.
At the lower filter notch settings (below 60 Hz), the no missing
codes performance of the device is at the 24-bit level. At the
higher settings, more codes will be missed until at the 1 kHz
notch setting; no missing codes performance is guaranteed
only to the 12-bit level. However, because the effective reso-
lution of the part is 10.5 bits for this filter notch setting, this
no missing codes performance should be more than adequate
for all applications.
The effective resolution of the device is defined as the ratio of
the output rms noise to the input full scale. This does not re-
main constant with increasing gain or with increasing band-
width. Table II is the same as Table I except that the output is
expressed in terms of effective resolution (the magnitude of the
rms noise with respect to 2 × VREF/GAIN, the input full scale).
It is possible to do post filtering on the device to improve the
output data rate for a given –3 dB frequency and also to further
reduce the output noise (see the Digital Filtering section).
Table I. Output Noise vs. Gain and First Notch Frequency
First Notch of
Filter and O/P –3 dB
Data Rate1 Frequency Gain of 1 Gain of 2
Typical Output RMS Noise (V)
Gain of 4 Gain of 8 Gain of 16
Gain of 32
Gain of 64
Gain of 128
10 Hz2
2.62 Hz 1.0
0.78
0.48
0.33
0.25
0.25
0.25
0.25
25 Hz2
6.55 Hz 1.8
1.1
0.63
0.5
0.44
0.41
0.38
0.38
30 Hz2
7.86 Hz 2.5
1.31
0.84
0.57
0.46
0.43
0.4
0.4
50 Hz2
13.1 Hz 4.33
2.06
1.2
0.64
0.54
0.46
0.46
0.46
60 Hz2
15.72 Hz 5.28
2.36
1.33
0.87
0.63
0.62
0.6
0.56
100 Hz3
26.2 Hz 13
6.4
3.7
1.8
1.1
0.9
0.65
0.65
250 Hz3
65.5 Hz 130
75
25
12
7.5
4
2.7
1.7
500 Hz3
131 Hz
0.6 × 103 0.26 × 103 140
70
35
25
15
8
1 kHz3
262 Hz
3.1 × 103 1.6 × 103 0.7 × 103 0.29 × 103 180
120
70
40
NOTES
1The default condition (after the internal power-on reset) for the first notch of filter is 60 Hz.
2For these filter notch frequencies, the output rms noise is primarily dominated by device noise, and, as a result, is independent of the value of the reference voltage.
Therefore, increasing the reference voltage will give an increase in the effective resolution of the device (that is, the ratio of the rms noise to the input full scale is
increased because the output rms noise remains constant as the input full scale increases).
3For these filter notch frequencies, the output rms noise is dominated by quantization noise, and, as a result, is proportional to the value of the reference voltage.
Table II. Effective Resolution vs. Gain and First Notch Frequency
First Notch of
Effective Resolution* (Bits)
Filter and O/P –3 dB
Data Rate Frequency Gain of 1 Gain of 2 Gain of 4 Gain of 8 Gain of 16
Gain of 32
Gain of 64
Gain of 128
10 Hz
2.62 Hz 22.5
21.5
21.5
21
20.5
19.5
18.5
17.5
25 Hz
6.55 Hz 21.5
21
21
20
19.5
18.5
17.5
16.5
30 Hz
7.86 Hz 21
21
20.5
20
19.5
18.5
17.5
16.5
50 Hz
13.1 Hz 20
20
20
19.5
19
18.5
17.5
16.5
60 Hz
15.72 Hz 20
20
20
19.5
19
18
17
16
100 Hz
26.2 Hz 18.5
18.5
18.5
18.5
18
17.5
17
16
250 Hz
65.5 Hz 15
15
15.5
15.5
15.5
15.5
15
14.5
500 Hz
131 Hz
13
13
13
13
13
12.5
12.5
12.5
1 kHz
262 Hz
10.5
10.5
11
11
11
10.5
10
10
NOTE
*Effective resolution is defined as the magnitude of the output rms noise with respect to the input full scale (i.e., 2 × VREF/GAIN). The above table applies for a VREF
of 2.5 V and resolution numbers are rounded to the nearest 0.5 LSB.
REV. G
–11–
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