Datasheet

AD7707
Rev. B | Page 17 of 52
OUTPUT NOISE FOR HIGH LEVEL INPUT CHANNEL
AIN3 (3 V OPERATION)
Table 13 shows the AD7707 output rms noise and peak-to-peak
resolution 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 ±5 V, 0 V to 5 V and 0 V to 10 V
ranges with a V
REF
of 1.225 V, VBIAS = 1.225 V, HICOM =
AGND, and AV
DD
= 3 V. These numbers are typical and are
generated at an analog input voltage of 0 V for unbuffered mode
of operation. The ±5 V, 0 V to 5 V, and 0 V to 10 V operating
ranges are only achievable in unbuffered mode when operating
at 3 V due to common-mode limitations on the input amplifier.
It is important to note that these numbers represent the
resolution for which there are no code flicker. They are not
calculated based on rms noise but on peak-to-peak noise.
Operating at a gain of 1 in unipolar mode provides a range of
0 V to +10 V. Operating the high level channel with a gain of 2
in bipolar mode provides a ±5 V operating range. Operating at
a gain of 2 in unipolar mode provides an operating range of 0 V
to 5 V. 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 modulator. Secondly, when
the analog input is converted into the digital domain, quantiza-
tion 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 13
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 13. Output RMS Noise/Peak-to-Peak Resolution vs. Gain and Output Update Rate @ +3 V AIN3 Unbuffered Mode Only
Filter First Notch
and Output
Data Rate
−3 dB
Frequency
0 V to 10 V Range ±5 V Range 0 to 5 V Range
RMS Noise P-P (Bits) RMS Noise P-P (Bits) RMS Noise P-P (Bits)
(μV) Resolution (μV) Resolution (μV) Resolution
MCLK IN = 2.4576 MHz
10 Hz 2.62 Hz 12.4 16 7.02 16 7.02 16
50 Hz 13.1 Hz 30.35 16 16.4 16 16.4 15.5
60 Hz 15.72 Hz 34.55 16 19.13 16 19.13 15
250 Hz 65.5 Hz 498 12.5 204 13 204 12
500 Hz 131 Hz 2266 10.5 1151 10.5 1151 9.5
MCLK IN = 1 MHz
4.05 Hz 1.06 Hz 13.9 16 7.3 16 7.3 16
20 Hz 5.24 Hz 32.2 16 17.4 16 17.4 15
25 Hz 6.55 Hz 33.4 16 18.57 16 18.57 15
100 Hz 26.2 Hz 430 13 200 13 200 12
200 Hz 52.4 Hz 2207 10.5 1048 10.5 1048 9.5