Data acquisition
have enabled overcoming many limitations. AD4134 is the first high precision dc to 400 kHz bandwidth ADC based on CTSD that achieves substantially higher performance specifications, while providing dc accuracy and, in turn, enabling the solution for a number of important system- level problems in high performance instrumentation applications. The AD4134 also integrates an asynchronous sample rate converter (ASRC) providing data at variable data rates derived from the fixed sampling speed of CTSD. The output data rate can be independent of modulator sampling frequency and can enable successful use of CTSD ADCs for different granular throughputs. The flexibility to change the output data rate at a granular level also enables users to use coherent sampling.
SIGNAL CHAIN BENEFITS OF AD4134 Alias Free
Inherent alias rejection removes the need for an antialiasing filter, which results in fewer components and a smaller solution size. More importantly, all the performance worries that come along with an antialiasing filter such as droop, errors such as offset, gain, and phase error, and noise in the system are no longer present.
Low Latency Signal Chain
An antialiasing filter adds significantly to the overall latency in the signal chain depending upon the rejection needed. Removal of the filter removes this delay completely and gets you to run precision conversion in noisy digital control loop applications.
Excellent Phase Matching
Having no antialiasing filter at the system level, phase matching in multichannel systems can be vastly improved. This makes it the right choice for applications demanding low channel-to-channel mismatch such as vibration monitoring, power measurements, data acquisition modules, and sonar.
Robustness with Interference Because of its inherent filtering action, CTSD ADCs are also immune to any kind of interference at the system level, as well from within the IC itself. In DTSD ADCs and SAR ADCs, care has to be taken such that there is less interference when the ADC is sampling. Also, there would be immunity from interference
Figure 15. Size comparison of discrete-time and continuous-time signal chain.
on power supply lines due to the inherent filtering action.
Resistive Inputs With constant resistive analogue inputs and reference inputs, the driver requirement can be completely removed. Again, all the performance worries such as errors like offset, gain, phase error, and noise to the system are no longer there.
Easy to Design The struggle to achieve the precision performance
is very minimal as the number of designed elements is significantly reduced. This result in faster design time, faster time to market for customers, easier BOM management, and reliability.
Size Removal of an antialiasing filter, a driver, and a reference buffer will significantly reduce the system board area. An instrumentation amplifier can be used to directly drive the ADC. For AD4134, as it is a differential input only ADC, a differential in- amp such as the LTC6373 can be used as a driver. The comparison in Figure 14 shows the signal chain for a discrete-time-based signal chain and a continuous-time-based signal chain. Our experiment shows 70% of area savings when compared to an equivalent discrete-time-based signal chain, making it an excellent choice for high density multichannel applications. In conclusion, the AD4134 offers significant system size reduction, simplifies the signal chain design, makes the system more robust, and reduces the overall time to market with easy design-in without trading any performance parameters demanded by precision instrumentation applications.
Figure 14. A discrete-time-based (left) and a continuous-time-based (right) signal chain comparison. Instrumentation Monthly September 2023 Analog Devices
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