Question

An 10-bit successive approximation A/D (Analog-to-digital) converter has the following specs: Minimum analog to digital conversion time 3×10^-3 second with the analog input voltage range: 0 to +6 volts. The A/D is used with a laser micrometer sensor that provides analog position feedback in the range of 0-0.02 m mapping linearly to the voltage of 0-1 volt with precision (accuracy) of 60 μm.

a) What is the maximum frequency that can be sampled without aliasing (Hz)?

b) What is the resolution of this A/D converter in volts? A/D Resolution (mV)?

c) What is the precision of measured position by using this A/D converter and the laser micrometer in meter (μm)? Precision?

d) Design efficient interface between A/D and the laser micrometer to reach the highest possible precision (accuracy) of measured position value. Draw the schematic of signal conditioning circuit and calculated the properties of required components.

e) Determine the precision of measured position with the integration of your designed signal conditioning circuit interface to the A/D converter?

Answer #1

Answering part -A of your question.

The given data specifically mentions about minimum conversion time of ADC which is 3×10^-3 second. Now a successive approximation type time for conversion directly depends on the number of bits being used and is thus constant for a given ADC

This can be used to calculate frequency by the relation F=
**1/T where T is the conversion time** This comes out
to be 333.33 hz

Now in order to Prevent aliasing by nyquist theorem the
frequency used must be half of that hence it must be 333.33hz/2 =
**166.65Hz**

We have a 16 bit analog to digital converter that is expected to
measure a 10 volt peak to peak ac signal with harmonic frequencies
up to 100 khz. Calculate the minimum clock rate required in these
two cases: (a) the counter scans voltages sequentially, (b) the
counter bisects the voltage interval at each clock pulse.

An 8-bit analog-to-digital converter (ADC) has a voltage range
of 0 to 14 V and a digitization uncertainty of ±1 LSB. What is the
maximum uncertainty if the digitization is for a 14 V signal? What
is the maximum uncertainty for a 16-bit ADC, and for 25-bit? If
this ADC has a conversion time of 34 μs, then what is the highest
frequency that can be accurately digitized while satisfying the
Nyquist criterion?

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