AMC1306E05_17 Datasheet, PDF (23/40 Pages) Texas Instruments – Small, High-Precision, Reinforced Isolated Delta-Sigma Modulators with High CMTI

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9 Application and Implementation
AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25
SBAS734 – MARCH 2017
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
9.1.1 Digital Filter Usage
The modulator generates a bitstream that is processed by a digital filter to obtain a digital word similar to a
conversion result of a conventional analog-to-digital converter (ADC). A very simple filter, built with minimal effort
and hardware, is a sinc³-type filter, as shown in Equation 2:
Hz
§
¨¨©
1
1
z
OSR
z¹
·³
¸¸¹
(2)
This filter provides the best output performance at the lowest hardware size (count of digital gates) for a second-
order modulator. All the characterization in this document is also done with a sinc³ filter with an oversampling
ratio (OSR) of 256 and an output word duration of 16 bits.
The effective number of bits (ENOB) is often used to compare the performance of ADCs and ΔΣ modulators.
Figure 50 shows the ENOB of the AMC1306 with different oversampling ratios. In this document, this number is
calculated from the SNR by using Equation 3:
SINAD 1.76 dB 6.05 dB uENOB
(3)
16
14
12
10
8
6
4
sinc³
2
sinc²
sinc¹
0
1
10
100
1000
OSR
D040
Figure 50. Measured Effective Number of Bits versus Oversampling Ratio
An example code for implementing a sinc³ filter in an FPGA is discussed in the Combining the ADS1202 with an
FPGA Digital Filter for Current Measurement in Motor Control Applications application note, available for
download at www.ti.com.
Copyright © 2017, Texas Instruments Incorporated
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