They have to be attenuated with analog filters. Noise peaks riding on signals near full scale have the potential to saturate the analog modulator of ADCs. Thus, it can protect the ADC's input circuitry. In case of input overvoltage, the analog filter also limits the input current and attenuates the input voltage. It also eliminates the effects of overdriven signals beyond the bandwidth of the filter to avoid modulator saturation. The analog low-pass filter can remove high frequency noise and interference from the signal path prior to the ADC conversion to help avoid contaminating the signal with aliased noise. In addition, all non-ideal filters introduce a phase delay or group delay.įigure 2. There can also be a transition band without steep falloff, which degrades noise attenuation around the cutoff frequency. The attenuation of the stop band is not infinite, which limits screening the noise out of band. If the pass band gain is not flat or exhibits ripples, this response may scale the fundamental signal. The response of some commonly used practical filters are shown in the colored lines in Figure 2. Furthermore, the stop band attenuation should reduce any residual out-of-band signal to zero. Ideal low-pass filters should have a steep transition band and excellent gain flatness in the pass band as shown by the brick wall dashed line in Figure 2. It is not the intent to address specific low-pass filter design techniques in this article but rather their application in ADC circuits.įigure 1. Since precision SAR and Σ-Δ ADCs are commonly sampling within the first Nyquist zone, this article will focus on low-pass filters. As shown in Figure 1, the data acquisition signal chain can utilize analog or digital filtering techniques, or even a combination of both. This article discusses the design challenges and considerations associated with implementing analog and digital filters into the ADC signal chain to achieve optimum performance. Users are facing more and more difficulties in limiting the signal chain noise, like in implementing filters, to take advantage of high-performance ADCs without limiting the ADCs' capabilities. Current SAR ADCs go up to 18-bit or even higher resolution at x-MSPS, while Σ-Δ ADCs can be 24- or 32-bit resolution at hundreds of kSPS. Precision analog-to-digital converters are popularly used in many applications, such as instrumentation and measurement, PLM, process control, and motor control. Here are some pointers to get the most out of them. Precision analog-to-digital converters can be tricky.
0 Comments
Leave a Reply. |