V

IN

Integrator 1

Integrator 2

0 V

DAC

V

1

V

2

V

4

V

5

V

3

CMP

f

CLKIN

23

AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25

www.ti.com

SBAS734C – MARCH 2017 – REVISED JANAURY 2020

Product Folder Links: AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25

Submit Documentation Feedback

Copyright © 2017–2020, Texas Instruments Incorporated

Feature Description (continued)

8.3.2 Modulator

The modulator implemented in the AMC1306 is a second-order, switched-capacitor, feed-forward ΔΣ modulator,

such as the one conceptualized in Figure 48. The analog input voltage VIN and the output V5 of the 1-bit digital-

to-analog converter (DAC) are differentiated, providing an analog voltage V1 at the input of the first integrator

stage. The output of the first integrator feeds the input of the second integrator stage, resulting in output voltage

V3 that is differentiated with the input signal VIN and the output of the first integrator V2. Depending on the polarity

of the resulting voltage V4, the output of the comparator is changed. In this case, the 1-bit DAC responds on the

next clock pulse by changing the associated analog output voltage V5, causing the integrators to progress in the

opposite direction and forcing the value of the integrator output to track the average value of the input.

Figure 48. Block Diagram of a Second-Order Modulator

The modulator shifts the quantization noise to high frequencies, as shown in Figure 48. Therefore, use a low-

pass digital filter at the output of the device to increase the overall performance. This filter is also used to convert

from the 1-bit data stream at a high sampling rate into a higher-bit data word at a lower rate (decimation). TI's

microcontroller families TMS320F2807x and TMS320F2837x offer a suitable programmable, hardwired filter

structure termed a sigma-delta filter module (SDFM) optimized for usage with the AMC1306 family. Also,

SD24_B converters on the MSP430F677x microcontrollers offer a path to directly access the integrated sinc-

filters for a simple system-level solution for multichannel, isolated current sensing. An additional option is to use a

suitable application-specific device, such as the AMC1210 (a four-channel digital sinc-filter). Alternatively, a field-

programmable gate array (FPGA) can be used to implement the filter.