AD7719 datasheet(14/40 Pages) AD

14 / 40 page

REV. 0

AD7719

–14–

FREQUENCY – Hz

–80

–160

100

–20

–40

–120

–140

–60

–100

SF = 69

OUTPUT DATA RATE = 19.8Hz

INPUT BANDWIDTH = 4.74Hz

FIRST NOTCH = 9.9Hz

50Hz REJECTION = –66dB, 50Hz 1Hz REJECTION = –60dB

60Hz REJECTION = –117dB, 60Hz 1Hz REJECTION = –94dB

Figure 8. Filter Profile with Default SF = 69 Giving Filter

Notches at Both 50 Hz and 60 Hz

FREQUENCY – Hz

–80

–160

100

–20

–40

–120

–140

–60

–100

SF = 255

OUTPUT DATA RATE = 5.35Hz

INPUT BANDWIDTH = 1.28Hz

50Hz REJECTION = –93dB, 50Hz 1Hz REJECTION = –93dB

60Hz REJECTION = –74dB, 60Hz 1Hz REJECTION = –68dB

Figure 9. Filter Profile with SF = 255

FREQUENCY – Hz

–140

–200

650

50 100 150 200 250 300 350 400 450 500 550 600

700

–20

–120

–160

–180

–60

–100

–40

–80

SF = 13

OUTPUT DATA RATE = 105Hz

INPUT BANDWIDTH = 25.2Hz

FIRST NOTCH = 52.5Hz

50Hz REJECTION = –23.6dB, 50Hz 1Hz REJECTION = –20.5dB

60Hz REJECTION = –14.6dB, 60Hz 1Hz REJECTION = –13.6dB

Figure 6. Filter Profile with SF = 13

FREQUENCY – Hz

–80

–160

100

–20

–40

–120

–140

–60

–100

SF = 82

OUTPUT DATA RATE = 16.65Hz

INPUT BANDWIDTH = 4Hz

50Hz REJECTION = –171dB, 50Hz 1Hz REJECTION = –100dB

60Hz REJECTION = –58dB, 60Hz 1Hz REJECTION = –53dB

Figure 7. Filter Profile with SF = 82

MAIN AND AUXILIARY ADC NOISE PERFORMANCE

Tables II to VII show the output rms noise and output peak-to-

peak resolution in bits (rounded to the nearest 0.5 LSB) for a

selection of output update rates on both the main and auxiliary

ADCs. The numbers are typical and generated at a differential

input voltage of 0 V. The output update rate is selected via the

SF7-SF0 bits in the Filter Register. It is important to note that

the peak-to-peak resolution figures represent the resolution for

which there will be no code flicker within a six-sigma limit. 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, 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 domi-

nant noise source. The numbers in the tables are given for the

bipolar input ranges. For the unipolar ranges the rms noise

numbers will be 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.

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