7.2.4 Bitstream Filtering

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). Equation 2 shows a sinc3-type filter, which

is a very simple filter built with minimal effort and hardware.

3

OSR

1

1

z

H z

1

z

§

·

¨

¸

¨

¸

©

¹

(2)

This filter provides the best output performance at the lowest hardware size (count of digital gates) for a second-

order modulator. All characterization in this document is also done with a sinc3 filter with an oversampling ratio

(OSR) of 256 and a 16-bit output word width.

The Combining the ADS1202 with an FPGA Digital Filter for Current Measurement in Motor Control Applications

application note discusses an example code. Use this example code for implementing a sinc3 filter in an FPGA.

This application note is available for download at www.ti.com.

For modulator output bitstream filtering, use a device from TI's C2000 or Sitara microcontroller families. These

families support multichannel dedicated hardwired filter structures that significantly simplify system level design

by offering two filtering paths per channel. One path provides high-accuracy results for the control loop and the

other provides a fast-response path for overcurrent detection.

A delta sigma modulator filter calculator is available for download at www.ti.com that aids in the filter design

and correct OSR and filter order selection. This calculator helps achieve the desired output resolution and filter

response time.

7.3 Best Design Practices

Place a capacitor at the input of the device (from IN to AGND) to filter the input signal; see the Input Filter Design

section. Do not leave the input of the AMC0136 unconnected (floating) when the device is powered up. If the

modulator input is left floating, the output bitstream is not valid.

www.ti.com

AMC0136

SBASAZ0 – AUGUST 2024

Copyright © 2024 Texas Instruments Incorporated

Submit Document Feedback

15

Product Folder Links: AMC0136