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An ADC (Analog-to-Digital Converter) is a fundamental component of analog electronics that converts an analog signal to a digital signal. The conversion process involves measuring the amplitude of the input analog signal at a regular time interval, and then representing the measured values as binary numbers. The resulting digital signal can then be processed by a digital system, such as a microcontroller, computer, or DSP (Digital Signal Processor).
Typology: Study notes
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C Quantizing & Encoding
S/H circuit Input analog Input analog signal signal Output digital Output digital signal signal
Analog Signal (^) Digital output in binary
There are two ways to best improve the accuracy of A/D conversion: increasing the resolution which improves the accuracy in measuring the amplitude of the analog signal. increasing the sampling rate which increases the maximum frequency that can be measured.
By: Todd Sifleet
Voltage-to-frequency, staircase ramp or single slope, charge balancing or redistribution, switched capacitor, tracking, and synchro or resolver
Fundamental components Integrator Electronically Controlled Switches Counter Clock Control Logic Comparator
At t<0, S 1 is set to ground, S 2 is closed, and counter=0. At t=0 a conversion begins and S 2 is open, and S 1 is set so the input to the integrator is Vin. S 1 is held for TINT which is a constant predetermined time interval. When S 1 is set the counter begins to count clock pulses, the counter resets to zero after TINT Vout of integrator at t=TINT is VINTINT/RC is linearly proportional to VIN At t=TINT S 1 is set so -Vref is the input to the integrator which has the voltage VINTINT/RC stored in it. The integrator voltage then drops linearly with a slop -Vref/RC. A compartor is used to determine when the output voltage of the integrator crosses zero When it is zero the digitized output value is the state of the counter.
Conversion result is insensitive to errors in the component values. Fewer adverse affects from “noise” High Accuracy
Slow Accuracy is dependent on the use of precision external components Cost
Uses the 2 N resistors to form a ladder voltage divider, which divides the reference voltage into 2 N equal intervals. Uses the 2 N -1 comparators to determine in which of these 2 N voltage intervals the input voltage Vin lies. The Combinational logic then translates the information provided by the output of the comparators This ADC does not require a clock so the conversion time is essentially set by the settling time of the comparators and the propagation time of the combinational logic.
Successive Approximation ADC Circuit
Successive Approximation ADC Process
Output
Is Vin > ½ ADC range? 0100 0000 If no, then test next bit Vref
Advantages Capable of high speed and reliable Medium accuracy compared to other ADC types Good tradeoff between speed and cost Capable of outputting the binary number in serial (one bit at a time) format. Disadvantages Higher resolution successive approximation ADC’s will be slower Speed limited to ~5Msps
Successive Approximation Example Example 10 bit ADC Vin= 0.6 volts (from analog device) V ref =1 volts Find the digital value of Vin N= n (N of possible states) N= Vmax-Vmin/N = 1 Volt/1024 = 0.0009765625V of Vref (resolution)
