原标题：ADI AD7793热电偶测量系统解决方案

　　ADI公司的 AD7792/3是高精度测量系统的低功耗低噪音模拟前端(AFE),包括三个差分模拟输出的低噪音16/24位Delta-Sigma ADC,仪表放大器能直接连接到ADC,增益设定为64,4.17Hz的噪音为40nV,工作电压2.7-5.25V, 主要用在热电偶测量,RTD测量,气体分析,工业过程控制,手持仪表,血液分析以及6位DVM等.本文介绍了AD7793主要特性,方框图, RTD和热电偶测量电路图以及采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统电路图和材料厂清单.

　　The AD7792/AD7793 are low power, low noise, complete analog front ends for high precision measurement applications. The AD7792/AD7793 contain a low noise 16-/24-bit Σ-Δ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. With a gain setting of 64, the rms noise is 40 nV when the update rate equals 4.17 Hz.

　　The devices contain a precision low noise, low drift internal band gap reference and can accept an external differential reference. Other on-chip features include programmable excitation current sources, burnout currents, and a bias voltage generator. The bias voltage generator sets the common-mode voltage of a channel to AVDD/2.

　　The devices can be operated with either the internal clock or an external clock. The output data rate from the parts is software-programmable and can be varied from 4.17 Hz to 470 Hz.

　　The parts operate with a power supply from 2.7 V to 5.25 V. They consume a current of 400 μA typical and are housed in a 16-lead TSSOP package.

　　AD7793主要特性:

　　Up to 23 bits effective resolution

　　RMS noise

　　40 nV @ 4.17 Hz

　　85 nV @ 16.7 Hz

　　Current: 400 μA typical

　　Power-down: 1 μA maximum

　　Low noise programmable gain instrumentation amp

　　Band gap reference with 4 ppm/°C drift typical

　　Update rate: 4.17 Hz to 470 Hz

　　3 differential inputs

　　Internal clock oscillator

　　Simultaneous 50 Hz/60 Hz rejection

　　Programmable current sources

　　On-chip bias voltage generator

　　Burnout currents

　　Power supply: 2.7 V to 5.25 V

　　–40°C to +105°C temperature range

　　Independent interface power supply

　　16-lead TSSOP package

　　Interface

　　3-wire serial

　　SPI®, QSPI™, MICROWIRE™, and DSP compatible

　　Schmitt trigger on SCLK

　　AD7793应用:

　　Thermocouple measurements

　　RTD measurements

　　Thermistor measurements

　　Gas analysis

　　Industrial process control

　　Instrumentation

　　Portable instrumentation

　　Blood analysis

　　Smart transmitters

　　Liquid/gas chromatography

　　6-digit DVM

　　图1.AD7793方框图

　　图2.采用AD7792/3的RTD应用电路图

　　图3.采用AD7792/3的热电偶测量电路图

　　采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统

　　Complete Thermocouple Measurement System Using the AD7793 24-Bit Sigma-Delta ADC

　　The circuit, shown in Figure 4, is a complete thermocouple system based on the AD7793 24-bit sigma-delta ADC. The AD7793 is a low power, low noise, complete analog front end for high precision measurement applications. The device includes a PGA, internal reference, internal clock, and excitation currents, thereby greatly simplifying the thermocouple system design.

　　图4.带冷端补偿的热电偶测量系统电路图(简化电路图:所有的连接和去偶电容未标)

　　图5. 热电偶测量系统外形图