Datasheet
AD7707
Rev. B | Page 15 of 52
OUTPUT NOISE FOR LOW LEVEL INPUT
CHANNELS (3 V OPERATION)
Table 9 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 bipolar
input ranges with a V
REF
of 1.225 V and an AV
DD
= 3 V. These
numbers are typical and are generated at an analog input
voltage of 0 V. Table 10 shows the rms noise and peak-to-peak
resolution when operating in buffered mode. It is important to
note that the peak-to-peak 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 and 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. The output noise
comes from two sources. The first is the electrical noise in the
semiconductor devices (device noise) used in the implementa-
tion of the modulator. 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 fre-
quency. 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 9 and Table 10 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 9. Output RMS Noise/Peak-to-Peak Resolution vs. Gain and Output Update Rate @ 3 V AIN1 and AIN2 Unbuffered Mode Only
Filter First Notch
and Output Data
Rate
−3 dB
Frequency
Typical Output RMS Noise in μV (Peak-to-Peak Resolution in Bits)
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
10 Hz 2.62 Hz 1.60 (16) 0.8 (16) 0.48 (16) 0.29 (16) 0.29 (16) 0.27 (15.5) 0.26 (14.5) 0.26 (13.5)
50 Hz 13.1 Hz 3.8 (16) 1.9 (16) 1.1 (16) 0.64 (16) 0.60 (15.5) 0.6 (14.5) 0.6 (13.5) 0.6 (12.5)
60 Hz 15.72 Hz 4.4 (16) 2.2 (16) 1.35 (16) 0.78 (16) 0.7 (15) 0.68 (14.5) 0.64 (13.5) 0.64 (12.5)
250 Hz 65.5 Hz 53 (13) 24 (13) 15 (13) 6.8 (13) 3.6 (12.5) 2.1 (12.5) 1.5 (12) 1.3 (11)
500 Hz 131 Hz 300 (10.5) 138 (10.5) 80 (10.5) 34 (10.5) 18 (10.5) 8.7 (10.5) 4.8 (10) 3.4 (10)
MCLK IN = 1 MHz
4.05 Hz 1.06 Hz 1.56 (16) 0.88 (16) 0.52 (16) 0.3 (16) 0.28 (16) 0.27 (15.5) 0.27 (14.5) 0.26 (13.5)
20 Hz 5.24 Hz 3.85 (16) 2.02 (16) 1.15 (16) 0.74 (16) 0.63 (15.5) 0.57 (14.5) 0.61 (13.5) 0.58 (12.5)
25 Hz 6.55 Hz 4.56 (16) 2.4 (16) 1.4 (16) 0.79 (16) 0.68 (15) 0.66 (14.5) 0.64 (13.5) 0.64 (12.5)
100 Hz 26.2 Hz 45.7 (13) 22 (13) 13.7 (13) 5.27 (13) 2.64 (13) 2 (12.5) 1.59 (12) 1.4 (11)
200 Hz 52.4 Hz 262 (10.5) 125 (10.5) 66 (10.5) 32.4 (10.5) 18.4 (10.5) 8.6 (10.5) 4.64 (10.5) 3.3 (10)
Table 10. Output RMS Noise/Peak-to-Peak Resolution vs. Gain and Output Update Rate @ 3 V AIN1 and AIN2 Buffered Mode Only
Filter First Notch
and Output Data
Rate
−3 dB
Frequency
Typical Output RMS Noise in μV (Peak-to-Peak Resolution in Bits)
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
10 Hz 2.62 Hz 1.80 (16) 1 (16) 0.7 (16) 0.41 (16) 0.41 (16) 0.41 (15) 0.41 (14) 0.41 (13)
50 Hz 13.1 Hz 4.1 (16) 2.4 (16) 1.5 (16) 1 (15.5) 0.91 (15) 0.89 (14) 0.86 (13) 0.83 (12)
60 Hz 15.72 Hz 5.1 (16) 3 (16) 1.8 (16) 1.1 (15.5) 0.94 (14.5) 0.94 (13.5) 0.99 (13) 0.99 (11.5)
250 Hz 65.5 Hz 50 (13) 27 (13) 12.3 (13) 6.4 (13) 4 (12.5) 2.7 (12.5) 2.2 (11.5) 1.8 (11)
500 Hz 131 Hz 275 (10.5) 125 (10.5) 80 (10.5) 39 (10.5) 16 (10.5) 8.9 (10.5) 5.2 (10) 4.2 (9.5)
MCLK IN = 1 MHz
4.05 Hz 1.06 Hz 1.75 (16) 1.18 (16) 0.67 (16) 0.44 (16) 0.41 (16) 0.44 (15) 0.43 (14) 0.43 (13)
20 Hz 5.24 Hz 4.21 (16) 2.5 (16) 1.48 (16) 1 (15.5) 0.94 (15) 0.96 (14) 0.89 (13) 0.86 (12)
25 Hz 6.55 Hz 5.15 (16) 2.8 (16) 1.8 (16) 1.15 (15.5) 1 (14.5) 1.02 (13.5) 0.96 (13) 1.03 (11.5)
100 Hz 26.2 Hz 46.1 (13) 24.3 (13) 13.6 (13) 6.71 (13) 4.1 (12.5) 2.54 (12.5) 2.3 (11.5) 2.15 (10.5)
200 Hz 52.4 Hz 282 (10.5) 123 (10.5) 66 (10.5) 35.3 (10.5) 14.8 (10.5) 9.91 (10.5) 5.48 (10) 4.01 (9.5)