AD7705/AD7706
Rev. C | Page 13 of 44
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 V
REF
of 1.225 V and a V
DD
= 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 V
REF
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
Typical Output RMS Noise in μV Filter First
Notch and
O/P Data Rate
−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 13.1 Hz 3.8 2.4 1.5 1.3 1.1 1.0 0.9 0.9
60 Hz 15.72 Hz 5.1 2.9 1.7 1.5 1.2 1.0 0.9 0.9
250 Hz 65.5 Hz 50 25 14 9.9 5.1 2.6 2.3 2.0
500 Hz 131 Hz 270 135 65 41 22 9.7 5.1 3.3
MCLK IN = 1 MHz
20 Hz 5.24 Hz 3.8 2.4 1.5 1.3 1.1 1.0 0.9 0.9
25 Hz 6.55 Hz 5.1 2.9 1.7 1.5 1.2 1.0 0.9 0.9
100 Hz 26.2 Hz 50 25 14 9.9 5.1 2.6 2.3 2.0
200 Hz 52.4 Hz 270 135 65 41 22 9.7 5.1 3.3
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
O/P Data Rate
−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 13.1 Hz 16 16 15 15 14 13 13 12
60 Hz 15.72 Hz 16 16 15 14 14 13 13 12
250 Hz 65.5 Hz 13 13 13 13 12 12 11 11
500 Hz 131 Hz 10 10 10 10 10 10 10 10
MCLK IN = 1 MHz
20 Hz 5.24 Hz 16 16 15 15 14 13 13 12
25 Hz 6.55 Hz 16 16 15 14 14 13 13 12
100 Hz 26.2 Hz 13 13 13 13 12 12 11 11
200 Hz 52.4 Hz 10 10 10 10 10 10 10 10
