Datasheet

AD7707
Rev. B | Page 16 of 52
OUTPUT NOISE FOR HIGH LEVEL INPUT CHANNEL
AIN3 (5 V OPERATION)
Table 11 shows the AD7707 output rms noise and peak-to-peak
resolution in unbuffered mode for the selectable notch and −3 dB
frequencies for the part, as selected by FS0, FS1, and FS2 of the
clock register. The numbers given are for the ±10 V, ±5 V, 0 to
5 V and 0 V to 10 V ranges with a V
REF
of 2.5 V, VBIAS = 2.5 V,
HICOM = AGND, and AV
DD
= 5 V. These numbers are typical
and are generated at an analog input voltage of 0 V. Table 12
meanwhile shows the output rms noise and peak-to-peak
resolution in buffered mode. It is important to 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. Operating the high level channel with a
gain of 2 in bipolar mode gives an operating range of ±10 V.
Operating at a gain of 2 in unipolar mode gives a range of 0 V
to +10 V. Operating the high level channel with a gain of 4 in
bipolar mode gives the ±5 V operating range. Operating at a gain
of 4 in unipolar mode gives an operating range of 0 V to 5 V.
Noise for all input ranges is shown in Output Noise For High Level
Input Channel, AIN3 section. The output noise comes from two
sources. The first is the electrical noise in the semiconductor
devices (device noise) used in the implementation of the modula-
tor. Secondly, when the analog input is converted into the digital
domain, quantization noise is added. The device noise is at a low
level and is independent of frequency. The quantization noise
starts at an even lower level but rises rapidly with increasing
frequency to become the dominant noise source. The numbers
in Table 11 and Table 12 are given for the bipolar input ranges.
For the unipolar ranges the rms noise numbers are the same as
the bipolar range, but the peak-to-peak resolution is now based
on half the signal range, which effectively means losing 1 bit of
resolution.
Table 11. Output RMS Noise/Peak-to-Peak Resolution vs. Gain and Output Update Rate @ 5 V AIN3 Unbuffered Mode Only
Filter First Notch
and Output Data
Rate
−3 dB
Frequency
±10 V Range ±5 V Range 0 V to 10 V Range 0 V to 5 V Range
RMS Noise
(μV)
P-P (Bits)
Resolution
RMS Noise
(μV)
P-P (Bits)
Resolution
RMS Noise
(μV)
P-P (Bits)
Resolution
RMS
Noise (μV)
P-P (Bits)
Resolution
MCLK IN = 2.4576 MHz
10 Hz 2.62 Hz 5.10 16 3.52 16 5.10 16 3.52 16
50 Hz 13.1 Hz 15.82 16 9.77 16 15.82 16 9.77 16
60 Hz 15.72 Hz 20.36 16 12.29 16 20.36 16 12.29 16
250 Hz 65.5 Hz 430 13 212 13 430 12 212 12
500 Hz 131 Hz 2350 10 1287 10 2350 9 1287 9
MCLK IN = 1 MHz
4.05 Hz 1.06 Hz 5.13 16 3.53 16 5.13 16 3.53 16
20 Hz 5.24 Hz 18.9 16 13.25 16 18.9 16 13.25 16
25 Hz 6.55 Hz 23.7 16 15.3 16 23.7 16 15.3 15.5
100 Hz 26.2 Hz 406 13 174 13 406 12 174 12
200 Hz 52.4 Hz 2184 10.5 1144 10.5 2184 9.5 1144 9.5
Table 12. Output RMS Noise/Peak-to-Peak Resolution vs. Gain and Output Update Rate @ 5 V AIN3 Buffered Mode Only
Filter First Notch
and Output Data
Rate
−3 dB
Frequency
±10 V Range ±5 V Range 0 V to 10 V Range 0 to 5 V Range
RMS Noise P-P (Bits) RMS Noise P-P (Bits) RMS Noise P-P (Bits) RMS Noise P-P (Bits)
(μV) Resolution (μV) Resolution (μV) Resolution (μV) Resolution
MCLK IN = 2.4576 MHz
10 Hz 2.62 Hz 7.4 16 5.2 16 7.4 16 5.2 16
50 Hz 13.1 Hz 22.2 16 14.3 16 22.2 16 14.3 16
60 Hz 15.72 Hz 26.6 16 15.85 16 26.6 16 15.85 16
250 Hz 65.5 Hz 475 13 187 13 475 12 187 12
500 Hz 131 Hz 2423 10.5 1097 10.5 2423 9.5 1097 9.5
MCLK IN = 1 MHz
4.05 Hz 1.06 Hz 7.63 16 5.45 16 7.63 16 5.45 16
20 Hz 5.24 Hz 20.25 16 13.3 16 20.25 16 13.3 16
25 Hz 6.55 Hz 23.5 16 14.6 16 23.5 16 14.6 15.5
100 Hz 26.2 Hz 377 13 210 13 377 12 210 12
200 Hz 52.4 Hz 2226 10.5 1132 10.5 2226 9.5 1132 9.5