AMC1303E0510 Datasheet, PDF(19/40 Page) Texas Instruments – Small, High-Precision, Reinforced Isolated Delta-Sigma Modulators with Internal Clock

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AMC1303E0510 Datasheet, PDF (19/40 Pages) Texas Instruments – Small, High-Precision, Reinforced Isolated Delta-Sigma Modulators with Internal Clock

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AMC1303E0510, AMC1303M0510, AMC1303E0520, AMC1303M0520

AMC1303E2510, AMC1303M2510, AMC1303E2520, AMC1303M2520

SBAS771 â JUNE 2017

Feature Description (continued)

8.3.2 Modulator

The modulator implemented in the AMC1303 (such as the one conceptualized in Figure 38) is a second-order,

switched-capacitor, feed-forward ÎÎ£ modulator. The analog input voltage VIN and the output V5 of the 1-bit

digital-to-analog converter (DAC) are subtracted, 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 subtracted from 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 its 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.

fCLKIN

VIN

Integrator 1

Integrator 2

CMP

DAC

Figure 38. Block Diagram of a Second-Order Modulator

The modulator shifts the quantization noise to high frequencies; see Figure 37. 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 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 called a

sigma-delta filter module (SDFM) optimized for usage with the AMC1303 family. Also, SD24_B converters on the

MSP430F677x microcontrollers offer a path to directly access the integrated sinc-filters, thus offering a 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.

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