The 8 channel data that uses individual ADC driver collects a system
[introduction] the main factor that affects data to collect a system includes: Speed, precision, power comsumption, enclose dimension and component cost, among them what meeting becomes crucial factor to depend on applied circumstance. How does article introduction use single operation amplifier to come 8 channel data collects drive the ADC in the system, reduce the cost of whole system and size thereby.
8 channel of AD7329, 12 add a mark, 1 MSPS ADC has true ambipolar input and 4 can become independent the process designing, input limits that can choose through software: ±4×VREF, ±2×VREF, ±VREF With 0-to-4×VREF. It uses agile design, via various applied requirement can be being satisfied after configuration. If the graph is shown 1 times, AD7329 by 8 channel multichannel answer is used implement and subsequently sampling maintains and successive approachs alignment of ADC, channel implement, composition of compatible interface of source of 2.5 V fiducial voltage and SPI.
Graph 1. AD7329 functional-block diagram
Imitate input channel passes multichannel answer to use implement road by to MUXOUT+ with MUXOUT–Cite a base. ADCIN+ with ADCIN–The join that cite a base maintains input switch to sampling (R1) and sampling capacitor (C2) , if pursue,2 are shown. Those who need an attention is, input source must offer needs electricity to be inputted with drive ADC, needs precision is built inside the time of 300 Ns sampling in ADC. Maintain switch to maintain ” to turn into from “ when sampling when “ sampling ” , the instantaneous recoil that ADC produces can affect input source. In the application that runs with highest sampling rate, the likelihood needs an input buffer amplifier to come drive ADC, maintain input source and sampling switch to be kept apart thereby come.
Graph 2. AD7329 imitate inputs structural — sheet to carry mode
The design of AD7329 is very agile, allow to be in MUXOUT+ with ADCIN+ bring an operation amplifier is placed between the foot. In the graph 3 in, super- low noise, super- low the input structure that lack fidelity AD797 operation amplifier will input source and AD7329 is kept apart come, increased input impedance and reduced the electricity that drive ADC place needs. This configuration still allows single operation amplifier with the biggest sampling frequency drive 8 imitate input channel, because this reduced component amount, board area and systematic cost.
Graph 3. MUXOUT With ADCIN The bumper between increased input impedance
Through configuring operation amplifier in order to realize gain, if the graph is shown 4 times, make AD7329 can get used to the signal inside millivolt limits, hold outstanding property at the same time. Faint signal is magnified by AD797, the signal that magnifies the course applies at ADCIN+ . To realize optimum behavior, can choose gain, so that spend the complete and dynamic limits of input signal use ADC completely.
Graph 4. MUXOUT With ADCIN The gain level between is helpful for millivolt input
Watch 1 showed the property that acquires inside ±10 V limits and gain (use 10 KHz input and rate of 1 MSPS sampling) . Notable is, it is in gain 1000 when, converter still can come true be more than the effective digit of 11 (ENOB) , realize the dynamic limits that comparatives with 21 ADC thereby. In addition, graph 3 in all advantages that show configuration also apply to this to use an occasion.
Express 1. AC function and gain
Certain application circumstance asks to change gain to have the input channel of different signal extent in order to suit. Below these circumstances, can use AD8250, AD8251, AD8253 to wait but amplifier of appearance of process designing gain (PGIA) will replace operation amplifier.
Referenced circuit
AN-0972, how is AD7329 helped reduce cost