Terminology » Sample & Hold ADC : Key Advantages and disadvantages

Sample & Hold ADC : Key Advantages and disadvantages

sample and hold adc analog to digital converter adc

Introduction : A Sample & Hold (S/H) ADC type includes a circuit that captures and holds the input voltage steady during conversion. This ensures that rapidly changing analog signals are accurately converted without distortion.

Sample & Hold ADC

flash type ADC

Figure : Flash Type ADC

Figure illustrates a block diagram of a parallel comparator ADC, also known as a 2-bit flash ADC. This is the fastest ADC type.

For an n-bit flash ADC, (2^n - 1) comparators and 2^n registers are required. Each comparator compares Vin to a different reference voltage, starting with Vref = 1/2 (LSB - Least Significant Bit). Op-amps are typically used as comparators here.

Advantages of sample & hold ADC

Following are some of the benefits of sample & hold ADC.

  1. Accurate Sampling : Holds the analog signal steady during conversion preventing variations that cause conversion errors.
  2. Prevents Distortion : Reduces signal distortion caused by ADC’s finite conversion time.
  3. Supports High Speed Signals which allows proper digitization of rapidly changing signals.
  4. Stable Input for ADC : Provides constant voltage to ADC input during conversion, improving accuracy.
  5. Enables multiplexing which facilitates switching between multiple analog channels without losing stability.

Disadvantages of sample & hold ADC

Following are some of the drawbacks of sample & hold ADC.

  1. Added Circuit Complexity : Requires extra components, increasing design complexity.
  2. Increased Cost : Additional hardware increases system cost.
  3. Hold Capacitor Leakage : Voltage may droop over time due to capacitor leakage, reducing accuracy.
  4. Switching Transient Noise : The switching action can introduce spikes or glitches.
  5. Finite Acquisition Time : Requires time to charge the capacitor to the correct voltage before holding, which can limit speed.

Conclusion : Sample & Hold ADCs improve conversion accuracy for fast varying signals but add circuit complexity and cost. They are essential in systems where signal stability during conversion is critical, such as high speed data acquisition.