AD7705/AD7706
OUTPUT NOISE (3 V OPERATION)
Table 7 shows the AD7705/AD7706 output rms noise for the
selectable notch and −3 dB frequencies for the parts, as selected
by FS0 and FS1 of the clock register. The numbers given are for
the bipolar input ranges with a VREF of 1.225 V and a VDD = 3 V.
These numbers are typical and are generated at an analog input
voltage of 0 V with the parts used in either buffered or unbuffered
mode. Table 8 shows the output peak-to-peak noise for the
selectable notch and −3 dB frequencies for the parts.
Note that these numbers represent the resolution for which
there is no code flicker. They are not calculated based on rms
noise, but on peak-to-peak noise. The numbers given are for
bipolar input ranges with a VREF of 1.225 V for either buffered or
unbuffered mode. These numbers are typical and are rounded
to the nearest LSB. The numbers apply for the CLKDIV bit of
the clock register set to 0.
Table 7. Output RMS Noise vs. Gain and Output Update Rate @ 3 V
Filter First
Notch and
O/P Data Rate
Typical Output RMS Noise in μV
−3 dB
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
MCLK IN = 2.4576 MHz
50 Hz
60 Hz
250 Hz
500 Hz
MCLK IN = 1 MHz
20 Hz
25 Hz
100 Hz
200 Hz
13.1 Hz
3.8
5.1
50
2.4
2.9
25
1.5
1.7
14
1.3
1.5
9.9
41
1.1
1.2
5.1
22
1.0
1.0
2.6
9.7
0.9
0.9
2.3
5.1
0.9
0.9
2.0
3.3
15.72 Hz
65.5 Hz
131 Hz
270
135
65
5.24 Hz
6.55 Hz
26.2 Hz
52.4 Hz
3.8
5.1
50
2.4
2.9
25
1.5
1.7
14
1.3
1.5
9.9
41
1.1
1.2
5.1
22
1.0
1.0
2.6
9.7
0.9
0.9
2.3
5.1
0.9
0.9
2.0
3.3
270
135
65
Table 8. Peak-to-Peak Resolution vs. Gain and Output Update Rate @ 3 V
Typical Peak-to-Peak Resolution in Bits
Filter First
Notch and
−3 dB
O/P 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
MCLK IN = 2.4576 MHz
50 Hz
60 Hz
250 Hz
500 Hz
MCLK IN = 1 MHz
20 Hz
25 Hz
100 Hz
200 Hz
13.1 Hz
16
16
13
10
16
16
13
10
15
15
13
10
15
14
13
10
14
14
12
10
13
13
12
10
13
13
11
10
12
12
11
10
15.72 Hz
65.5 Hz
131 Hz
5.24 Hz
6.55 Hz
26.2 Hz
52.4 Hz
16
16
13
10
16
16
13
10
15
15
13
10
15
14
13
10
14
14
12
10
13
13
12
10
13
13
11
10
12
12
11
10
Rev. C | Page 13 of 44
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