CM1110 ΔΣ ADC ,4-channel, 2kSPS, low-power, 16 bit

Operating Principle

The CM1110 is a compact, low-power, 16-bit ΔΣ ADC that integrates multiple functions to reduce system cost and component count in small-signal sensor measurement applications.

In addition to the ΔΣ ADC core and a single-cycle settling digital filter, the device integrates a low-noise, high-input-impedance programmable PGA, an internal voltage reference, and a clock oscillator. It also includes a high-accuracy precision temperature sensor and two matched programmable current sources (IDACs). An internal low-side power switch simplifies the design of low-power bridge sensors. The device can be configured through four registers and controlled via six commands using an SPI mode 1–compatible interface. The functional block diagram of the device is shown below.

The CM1110 measures the differential input signal VIN (the voltage difference between AINP and AINN). The converter core consists of a differential switched-capacitor ΔΣ modulator and a digital filter. The digital filter processes the high-speed bitstream output from the modulator and produces a digital code proportional to the input voltage.

The CM1110 provides two conversion modes: single-shot conversion mode and continuous conversion mode. In single-shot mode, the device performs one conversion on the input signal as requested, stores the result in the internal data buffer, and then enters a low-power state. For systems that require only periodic conversions or remain idle for long intervals between conversions, single-shot mode can significantly reduce power consumption. In continuous conversion mode, a new conversion starts immediately after the previous one completes. Data can be read at any time without concern for data corruption, and the data read represents the result of the most recent conversion.

Input Multiplexer

The CM1110 features a highly flexible input multiplexer, as shown in the figure below. It can measure four single-ended signals, two differential signals, or a combination of two single-ended signals and one differential signal. The multiplexer is configured through the MUX[3:0] register.

When measuring single-ended signals, the negative analog input (AINN) is internally connected to AVSS through the multiplexer. The ADC input can be selected as either the analog supply voltage divided by six, (AVDD – AVSS)/6, or the external reference voltage divided by six, (VREFPx – VREFNx)/6, enabling monitoring of the system operating status.

The multiplexer can also route the two programmable current sources to any analog input (AINx) or to any reference pin (REFP0, REFN0). Electrostatic discharge (ESD) diodes connected to AVDD and AVSS protect the inputs. To prevent the ESD diodes from conducting, the absolute voltage of all inputs must remain within the range specified by Equation (1):

AVSS − 0.3 V < VAINx < AVDD + 0.3 V (1)

If the voltage at an input pin may exceed the limits above, external Schottky clamp diodes or series resistors should be used to limit the input current to a safe level (see the Absolute Maximum Ratings table). Overdriving unused input pins on the device may affect ongoing conversions; in such cases, external Schottky diodes are recommended to clamp the signals.

Application of High-Precision, Low-Power ADC (CM1110) in Industrial Automation

1. Introduction

The CM1103/CM1106 are highly integrated, high-precision, low-power, and low-cost ADCs introduced by Simomo Microelectronics. With a sampling resolution of up to 7 µV, they can meet the requirements of most temperature sensor measurement applications. Their input impedance of several megaohms allows the ADCs to be directly connected to most resistive sensors without degrading sensor accuracy.

The CM110x series provides both I²C and SPI interfaces, making it easy for customers to interface with different processors. The CM1106 also integrates a high-precision internal temperature sensor, which can be directly used for PCB temperature measurement and cold-junction compensation in thermocouple applications.

2. Features of the CM110x

• Single-supply operation from 2.5 V to 5.5 V

• Ultra-low power consumption: 270 µA (continuous conversion mode)

• Sleep mode current: 2 µA

• Programmable output data rate: 6.25 SPS to 2 kSPS

• Integrated high-precision voltage reference with 10 ppm/°C temperature drift

• Programmable analog input range: ±0.256 V to ±6.144 V

• High-precision internal temperature sensor (CM1106)

• Integrated programmable comparator (CM1103)

• Four single-ended inputs / two differential input channels

3. Solution Overview

With the rapid development of industrial automation and increasing factory intelligence, industrial automation instruments have been evolving from analog instruments toward digital instruments in recent years. With the aid of microcontrollers and application-specific integrated circuits, industrial automation products are gradually becoming more intelligent.

Temperature is a critical parameter in industrial production, and temperature sensors play a vital role throughout the industrial automation field. Based on different sensing technologies, temperature sensors are available in many forms, such as infrared temperature sensors, resistance temperature detectors, thermistors, thermocouples, and RTD temperature sensors. All of these temperature measurement applications are particularly well suited for signal conditioning and data acquisition using the CM110x series.

In addition to temperature sensors, the CM110x—leveraging its inherent advantages—is especially suitable for a wide range of industrial sensing applications, such as resistive level sensors, resistive gas sensors, water quality analysis, and turbidity meters. These sensors typically have high output impedance and relatively low sensitivity, often requiring high-precision operational amplifiers for signal conditioning and amplification.

4. Product Advantages

The CM110x combines high input impedance, high precision, and low power consumption, offering significant advantages in various industrial sensing applications. It helps customers increase the level of integration in industrial transmitters while reducing overall system cost and power consumption.