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ADI公司的 AD7792/3是高精度測量系統的低功耗低噪音模擬前端(AFE),包括三個差分模擬輸出的低噪音16/24位Delta-Sigma ADC,儀表放大器能直接連接到ADC,增益設定為64,4.17Hz的噪音為40nV,工作電壓2.7-5.25V, 主要用在熱電偶測量,RTD測量,氣體分析,工業過程控制,手持儀表,血液分析以及6位DVM等.本文介紹了AD7793主要特性,方框圖, RTD和熱電偶測量電路圖以及采用AD7793 24位Sigma-Delta ADC完整的熱電偶測量系統電路圖和材料廠清單. 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應用: Thermocouple measurements RTD measurements Thermistor measurements Gas analysis Industrial process control Instrumentation Portable instrumentation Blood analysis Smart transmitters Liquid/gas chromatography 6-digit DVM 
圖1.AD7793方框圖
圖2.采用AD7792/3的RTD應用電路圖
圖3.采用AD7792/3的熱電偶測量電路圖 采用AD7793 24位Sigma-Delta ADC完整的熱電偶測量系統 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.
圖4.帶冷端補償的熱電偶測量系統電路圖(簡化電路圖:所有的連接和去偶電容未標)
圖5. 熱電偶測量系統外形圖
CN0206[2].pdf
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AD7792_7793[2].pdf
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