[AD7124 Series] A/D converter that achieves low power consumption despite being a Σ-Δ type

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Products that solve problems with Σ-Δ AD converters

A/D converters are used to convert analog signals from sensors etc. into digital signals. Additionally, when a high-precision, high-resolution A/D converter is required, a Σ-Δ converter is generally used. However, among high-precision A/D converters, Σ-Δ converters consume a large amount of current, which poses a major problem when used in products with limited power such as portable equipment.

We would like to introduce the AD7124 series, a Σ-Δ type A/D converter with 24-bit resolution, provided by Analog Devices, Inc., which solves this problem.

Article header library 121641 pic01 2 — AD7124シリーズ評価ボード

The AD7124 series has high accuracy and high resolution, as it is also used in "Soil moisture and pH measurement sensor shield - CN0398 (EVAL-CN0398-ARDZ)" introduced in Accelerate development with Arduino compatible development support platform. It is the perfect product for demanding and low consumption applications.

低消費のヒミツ

The AD7124 series is characterized by having three selectable power modes: full power, middle power, and low power. The power modes can be easily switched by simply changing the setting register, allowing you to flexibly respond to the required specifications.

しかも、低ノイズ

High-precision A/D converters also need to pay attention to noise. Naturally, the AD7124 series is a low noise product.

Current consumption and RMS noise value in each power mode

power mode	消費電流(Typ.)	rms noise
フルパワー	930μA	24 nV rms @ 1.17 SPS、ゲイン=128
ミドルパワー	355μA	20 nV rms @ 2.34 SPS、ゲイン=128
ローパワー	255μA	23 nV rms @ 9.4 SPS、ゲイン=128

低消費だけじゃない、すべての機能を1パッケージに

The AD7124 series includes the AD7124-4 with 4 differential input channels and the AD7124-8 with 8 differential input channels. Both are low power, low noise, 24-bit Σ-Δ A/D converters that incorporate all necessary functions.

Article header library 121641 pic02 2 — 必要な機能をすべて内蔵したAD7124シリーズ

Main function

function	overview
低ノイズPGA	A low-noise gain stage allows even small amplitude signals to be interfaced directly to the A/D converter.
高精度リファレンス	高精度基準電圧を内蔵しています。
選択可能な励起電流源	It can be used to measure temperature with thermistors and resistance temperature sensors, and to measure resistance objects.
クロック発振器	Built-in A/D converter operating clock.
バイアス電圧源	熱電対を用いた温度測定に利用できます。
GPO	汎用デジタル出力を備えています。
Temperature sensor	IC内部の温度を測ることができます。
digital filter	It has a built-in digital filter that achieves high resolution.
Temperature sensor	IC内部の温度を測ることができます。
セルフテストキャリブレーション	-

なんと、機能安全にも対応できる

The AD7124 series has various built-in functions for functional safety, making it an ideal product for those considering functional safety. It also has diagnostic functions, so multiple diagnostic functions enable designs that support functional safety.

機能だけじゃない、シミュレーションツールも充実

The "Virtual Eval Tool - BETA" is a simulation tool that supports over 100 A/D converter products and can simulate various characteristics such as noise, distortion, FFT, resolution, timing diagrams, and frequency response without the need for an actual device. The performance data used is model data on Analog Devices' server, so you can always get the latest simulation results. Of course, you can also set any parameters, so you can simulate performance before preparing an evaluation board, etc.

The Virtual Eval Tool - BETA is available free of charge by accessing the Analog Devices website.
http://beta-tools.analog.com/virtualeval/

Article header library 121641 pic04 2 — Virtual Eval Tool - BETA

シミュレーションツールは本当に使えるの？

The most important thing to note about simulation is whether the results are the same as those of an actual device. Here, we will compare the noise results of an evaluation board and a simulator.

The evaluation board used was the EVAL-AD7124-8SDZ. This evaluation board can be connected to a capture board (EVAL-SDP-CB1Z) that interfaces with a PC, and by using the software dedicated to the evaluation board, performance data can be confirmed on a GUI on a PC without an oscilloscope.

ノイズ測定時の設定は、いずれも下記の設定で確認しました。

設定条件

Setting items	set value	remarks
ADC/FilterのFS	1	ADCのサンプリングレートを最も早い設定に変更
ポストフィルター	0	-
Power Mode	Low	-
Other settings	デフォルト設定のまま	-

結果は・・

It can be seen that the verification results on the simulator and the actual machine are almost the same.

Article header library 121641 pic05 1 — Evaluation Board

The upper waveform is the measurement result on the evaluation board, and the lower waveform is the simulation result. The peak-to-peak noise was 470μV compared to the actual measurement of 356.44μV. The RMS noise was 72μV compared to the actual measurement of 72.58μV.

Article header library 121641 pic06 1 — シミュレーション（Virtual Eval Tool - BETA）

At the end

If your application requires a 24-bit Σ-Δ A/D converter with multiple channels, low power consumption, high accuracy, and high resolution, be sure to consider the AD7124 series.