An-607

AN-607
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Selecting a Low Bandwidth (<15 kSPS) Sigma-Delta ADC
by Mary McCarthy
INTRODUCTION
PRESSURE MEASUREMENT
Analog Devices, Inc., has a wide range of low bandwidth, high
resolution Σ-Δ ADCs. Along with the ADC, these devices
contain current sources, a multiplexer, a PGA, and analog input
buffers on-board. This application note identifies some of the
applications in which the ADCs are used and also identifies the
most suitable ADCs for each application.
Requirements: Low level differential analog inputs with a high
level differential reference input for ratiometric operation.
Optional features include an auxiliary ADC that can be used for
temperature compensation.
NUMBER OF BITS
16-Bit: AD7705, AD7706, AD7707, AD7708, AD7709,
AD7715, AD7788, AD7790, AD7792, AD7795, AD7796,
AD7798
24-Bit: AD7710, AD7711, AD7711A, AD7712, AD7713,
AD7714, AD7718, AD7719, AD7730, AD7730L, AD7731,
AD7732, AD7734, AD7738, AD7739, AD7782, AD7783,
AD7787, AD7789, AD7791, AD7793, AD7794, AD7797,
AD7799
MULTICHANNEL APPLICATIONS
High Throughput: AD7731, AD7734, AD7738, AD7739
Low Throughput: AD7708/AD7718, AD7714,
AD7794/AD7795
TEMPERATURE MEASUREMENT
For thermal diode and RTD applications, current sources are
required.
Thermocouple: AD7714, AD7719, AD7792/AD7793,
AD7794/AD7795
Thermal Diode: AD7709
RTD: AD7711, AD7719, AD7783, AD7792/AD7793,
AD7794/AD7795
AD7710, AD7714, AD7719, AD7730, AD7798/AD7799
WEIGH SCALE MEASUREMENT
Requirements: Low level differential analog inputs with a high
level differential reference input for ratiometric operation. Optional
features include an auxiliary ADC that can be used for temperature
compensation, fast-step, ac excitation, a reference detect circuit,
and increased filter rejection in the out-of-band region.
AD7714, AD7719, AD7730, AD7730L, AD7796/AD7797,
AD7798/AD7799
LOW POWER
AD7705/AD7706, AD7714, AD7715, AD7719, AD7787,
AD7788/AD7789, AD7790, AD7791, AD7792/AD7793,
AD7794/AD7795, AD7796/AD7797, AD7798/AD7799
HIGH ANALOG INPUT VOLTAGES (±10 V)
AD7707, AD7712, AD7732, AD7734
RAIL-TO-RAIL ON-CHIP BUFFERS
AD7708/AD7718, AD7709, AD7719, AD7782, AD7783,
AD7787, AD7790, AD7791
BIPOLAR INPUTS (±2.5 V)
AD7710, AD7711, AD7712
PIN CONFIGURABLE
AD7782, AD7783
Rev. E | Page 1 of 2
AN-607
Table 1. Summary of Low Bandwidth Σ-Δ ADCs
Part No.
Bits
p-p
Resolution
@ Max
Range (Bits)
p-p
Resolution
@ Data
Rate (Hz)
AIN
Channels
AD7701
AD7703
AD7705
AD7706
AD7707
AD7708
AD7709
AD7710
AD7711
AD7711A
AD7712
AD7713
AD7714
AD7715
AD7718
AD7719
AD7730
16
20
16
16
16
16
16
24
24
24
24
24
24
16
24
24
24
16
17
16
16
16
16
16
17.5
17.5
17.5
17.5
16
17.5
16
18.5
18.5
17
4000
4000
60
60
60
20
20
60
60
60
60
20
60
60
20
20
200
1
1
2
3
3
10
4
2
2
2
2
3
5
1
10
5
2
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
AD7730L
24
17
200
2
Y
Y
AD7731
24
17
800
5
Y
Y
AD7732
24
16
2000
2
Y
Y
AD7734
24
16
2000
4
Y
Y
AD7738
24
16
8500
8
Y
Y
AD7739
24
16
4000
8
Y
Y
AD7782
AD7783
AD7787
AD7788
AD7789
AD7790
AD7791
AD7792
AD7793
AD7794
AD7795
AD7796
AD7797
AD7798
24
24
24
16
24
16
24
16
24
24
16
16
24
16
18.5
18.5
19
16
19
16
19
16
19
19
16
15.5
15.5
16
20
20
16.6
16.6
16.6
16.6
16.6
16.6
16.6
16.6
16.6
16.6
16.6
16.6
2
1
2
1
1
1
1
3
3
6
6
1
1
3
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
AD7799
24
19
16.6
3
Y
Y
On-Chip
PGA
On-Chip
AIN
Buffer
Y
Y
Y
Y
Y
On-Chip
Current
Source
Y
Y
Y
Y
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN03180-0-10/06(E)
Rev. E | Page 2 of 2
Y
Y
Y
Y
Y
AVDD/
DVDD (V)
Power
Supply
Current
(mA)
Price
($/1k)
5
5
0.3
0.3
0.28
1.28
1.25
5
5
5
5
0.7
0.35
0.35
1.28
1.5
13
15.70
13.26
4.12
4.12
4.46
3.98
3.89
14.45
15.30
15.30
13.20
16.15
8.28
5.65
5.24
8.76
11.60
13
9.55
13.5
9.86
18
8.50
18
8.50
18
7.77
5
5
3/5
3/5
3/5
3/5
3/5
5
5
5
5
5
3/5
3/5
3/5
3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
AVDD: 5
DVDD: 3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
3/5
14
7.65
1.3
1.3
0.13
0.065
0.065
0.13
0.13
0.40
0.40
0.40
0.40
0.25
0.25
0.30
4.25
4.25
3.80
1.99
2.95
2.96
3.83
3.99
5.10
4.80
4.40
2.75
3.35
3.80
3/5
0.38
4.35
Comments
10 Hz bandwidth
10 Hz bandwidth
Two current sources
One current source
Dual ADC
Weigh scale
Weigh scale
Fast channel
switching
Fast channel
switching
Fast channel
switching
Fast channel
switching
Read-only
Read-only
Low power
Low power
Low power
Low power
Low power
On-chip reference
On-chip reference
High channel count
High channel count
Weigh scale
Weigh scale
Weigh scale/
pressure
Weigh scale/
pressure
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