6 Detailed Description

6.1 Overview

The AMC0136 is a precision, single-ended input, isolated amplifier with a high input-impedance and wide

input voltage range. The bufffered input stage of the device drives a second-order, CMOS, delta-sigma (ΔΣ)

modulator. The isolated output of the converter (DOUT) provides a stream of digital ones and zeros synchronous

to the external clock applied to the CLKIN pin. The time average of this serial output is proportional to the analog

input voltage.

The modulator shifts the quantization noise to high frequencies. Therefore, use a digital low-pass digital filter,

such as a sinc filter at the device output to increase overall performance. This filter also converts from the

1-bit data stream at a high sampling rate into a higher-bit data word at a lower rate (decimation). Use a

microcontroller (μC) or field-programmable gate array (FPGA) to implement the filter.

The overall performance (speed and resolution) depends on the selection of an appropriate oversampling ratio

(OSR) and filter type. A higher OSR results in higher resolution while operating at a lower refresh rate. A lower

OSR results in lower resolution, but provides data at a higher refresh rate. Multiple filters can run in parallel.

For example, a low OSR filter for fast overvoltage detection and a high OSR filter for high resolution voltage

measurement.

The silicon-dioxide (SiO2) based capacitive isolation barrier supports a high level of magnetic field immunity;

see the ISO72x Digital Isolator Magnetic-Field Immunity application note. The AMC0136 uses an on-off keying

(OOK) modulation scheme to transmit data across the isolation barrier. This modulation and the isolation barrier

characteristics, result in high reliability in noisy environments and high common-mode transient immunity.

6.2 Functional Block Diagram

DVDD

DOUT

DGND

AGND

IN

AGND

AVDD

CLKOUT

Modulator

Digital

Interface

6.3 Feature Description

6.3.1 Analog Input

The single-ended, high-impedance input stage of the AMC0136 feeds a second-order, switched-capacitor, feed-

forward ΔΣ modulator. The modulator converts the analog signal into a bitstream that is transferred across the

isolation barrier, as described in the Isolation Channel Signal Transmission section.

There are two restrictions on the analog input signal IN. First, if the input voltage VIN exceeds the range specified

in the Absolute Maximum Ratings table, limit the input current to the absolute maximum value because the

electrostatic discharge (ESD) protection turns on. Secondly, the linearity and parametric performance of the

device is specified only when the analog input voltage remains within the linear full-scale range (VFSR). See the

Recommended Operating Conditions table.

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AMC0136

SBASAZ0 – AUGUST 2024

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