In last month's blog post we introduced the applications requiring precision and wide bandwidth and focused on the output drive signal chain built around AD3552R. In this chapter we will analyze how those applications can benefit from a faster precision drive circuit.

Fast Precision DACs make a new category of products on their own. They aim at combining the accuracy of traditional precision DACs with the speed of high-speed DACs. Certainly, Fast DACs do not achieve hundreds of MSPS and there is a good reason for that.

Precision means reproducing the same output level across voltage, temperature and process. A key parameter of precision applications is the instant amplitude of the signal and the goal for a Fast Precision DAC is reaching the right value as quickly as possible. The bandwidth required to settle quickly to high accuracy is much more than the frequency of the underlying signals.

On the other hand, high-speed DACs are intended for passband applications where the bandwidth of the signal is similar to the bandwidth of the DAC because information is encoded in the spectral features of the signal rather than in its instant value.

Main Application Groups

Open-loop applications. The DAC drives a circuit whose response depends uniquely on the accuracy of the converter and the signal chain. Response time is dominated by data transfer and settling times. The lower the response time, the faster the measurements can be taken. For example, a scanning electron microscope, where the sample is taken when the beam has settled on the spot.

Closed-loop applications. The DAC drives a circuit whose response is monitored by an ADC. Response time depends on the latency of the digital processing chain including the converters and the settling time of the signal chain. The higher the sampling rate the shorter the delay of the digital processing circuit. For example, the emulation of the sensors and actuators of an electric power train.

Multi-market applicability of Fast Precision DACs

Scanning Electron Microscopes. DACs are used to steer the electron beam to produce a raster on the sample producing tens of millions of pixels. A Fast DAC can reduce imaging time from minutes to seconds.

RF Power and SMUs. Driving a load at constant power requires continuous adjustment of the control signals. The faster the DAC and the ADC, the faster the variations that the circuit can compensate. For example, a spectrum analyzer sweeping large bandwidth and compensating for imperfect SWR at each frequency.

Hardware in the Loop. This is a closed loop application where DACs and ADCs are used to test or emulate the response of a system. The bandwidth and response time of the closed-loop system depends on both the ADC and DAC. With the emergence of Fast Precision DACs these systems are taking a big leap ahead in performance. This technology has many applications in automotive testing industry.

 Electrical Impedance Spectroscopy / Tomography. This emerging imaging technique offers high resolution and physiological differentiation of tissues. Fast Precision DACs can replace DDS generators allowing simultaneous impedance measurement at various frequencies using OFDM-based signals.
 Gas Spectrometry. Gas spectrometers require a combination of DC and AC to drive the electrodes exciting the gas molecules. The speed and accuracy of a Fast Precision DAC can replace a combination of traditional precision DACs and DDS generators.

Conclusion

Fast Precision DACs not only pave the way for new applications but also help to boost the performance of traditional applications. In the next episode of this series we will cover an emerging application: Hardware in the Loop.

Precision Wide Bandwidth Solutions

 Precision Wide Bandwidth Signal Chains 

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