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3 Analog Interface
The ADS1258EVM is designed for convenient interfacing with analog input signals. This section covers
the details of the front-end circuit, including jumper configurations for different input test signals and board
connectors for signal sources.
3.1 Analog Input Options
The ADS1258EVM allows for up to 16 single-ended inputs or eight differential inputs, as well as combinations of
single-ended and differential inputs. As shown in
and J2 on the EVM.
R59
1.00k
R46
AIN7
1.00k
AIN6
AIN5
AIN4
R39
1.00k
R37
1.00k
J1
1
AIN7
2
AIN6
Differential-Mode Input Anti-Aliasing Filter
3
AIN5
4
AIN4
3-dB Cutoff: 168.51 kHz
AIN3
5
AIN2
6
Attenuation at Modulator Data Rate (8 MHz): 33.49 dB
7
AIN1
8
AIN0
R33
1.00k
R28
AIN3
1.00k
AIN2
AIN1
AIN0
R26
1.00k
R22
1.00k
Figure 3-1. ADS1258EVM Analog Input Channels and Filtering
Each analog input signal passes through a set of low-pass filters to prevent aliasing. The differential filters
have a 3-dB cutoff of 168.5 kHz, resulting in 33.49 dB of attenuation at the 8-MHz modulator frequency. As an
example,
Figure 3-1
shows that capacitor C13 and resistors R22 and R26 create the differential filter between
analog inputs AIN0 and AIN1. The common-mode filters have a 3-dB cutoff of 3.37 MHz. As an example,
3-1
shows that capacitor C11 and resistor R22 create the common-mode filter for analog input AIN0. Precision
5% C0G or NPO-type capacitors and 0.1% resistors are used in the analog signal chain to reduce measurement
error.
Use adjacent input pins when measuring differential input signals to benefit from differential filtering and to
achieve best performance. For example, AIN0 and AIN1 are set up for differential signaling because C13
connects these two inputs. Conversely, do not use AIN1 and AIN2 as a differential pair because there is no
capacitor connecting these two inputs.
SBAU126E – MAY 2007 – REVISED JUNE 2023
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Figure
A7
C35
47pF
C33
470pF
C31
GND
47pF
A6
A5
C29
47pF
C27
470pF
C25
GND
47pF
A4
A3
C23
47pF
C21
470pF
C18
GND
47pF
A2
A1
C15
47pF
C13
470pF
GND
C11
47pF
A0
Copyright © 2023 Texas Instruments Incorporated
3-1, connect analog input signals to terminal blocks J1
R60
1.00k
R47
AIN15
1.00k
AIN14
AIN13
AIN12
R40
1.00k
R38
1.00k
J2
1
AIN15
2
AIN14
3
AIN13
4
AIN12
5
AIN11
6
AIN10
AIN9
7
AIN8
8
R34
1.00k
R29
AIN11
1.00k
AIN10
AIN9
AIN8
R27
1.00k
R23
1.00k
ADS1258EVM-PDK Evaluation Module
Analog Interface
A15
C36
47pF
C34
470pF
C32
GND
47pF
A14
A13
C30
47pF
C28
470pF
C26
GND
47pF
A12
Common-Mode Input Anti-Aliasing Filter
3-dB Cutoff: 3.37 MHz
A11
C24
47pF
C22
470pF
C19
GND
47pF
A10
A9
C16
47pF
C14
470pF
GND
C12
47pF
A8
Figure
5
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