SBAS789B October 2017 – April 2020 AMC1106E05 , AMC1106M05
PRODUCTION DATA.
The modulator implemented in the AMC1106 (such as the one conceptualized in Figure 42) is a second-order, switched-capacitor, feed-forward ΔΣ 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.
The modulator shifts the quantization noise to high frequencies; see Figure 41. 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 family MSP430F67x offers a path to directly access the integrated sinc-filters of the SD24_B ADCs for a simple system-level solution for multichannel, isolated current sensing. Also, the microcontroller families TMS320F2807x and TMS320F2837x offer a suitable programmable, hardwired filter structure termed a sigma-delta filter module (SDFM) optimized for usage with the AMC1106. 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.