Summary
Highlights
ADC (Analog-to-Digital Converter) converts analog signals to digital, while DAC (Digital-to-Analog Converter) does the inverse. These converters are present in everyday devices like smartphones for tasks such as streaming music or making calls, converting signals back and forth between analog and digital domains.
Most natural signals are analog, but they are susceptible to noise and difficult to process or store. Digital signals are less prone to noise and are easier to manage, hence the need for converting analog signals to digital for processing and storage. DAC is then used to retrieve the analog signal when needed, although these conversions are not lossless due to information loss.
Analog signals have infinite resolution as they can take any value within a range. Digital signals are discrete in time and amplitude. The conversion process from analog to digital involves three main steps: sampling, quantization, and encoding. Each step contributes to the digital representation of the analog signal.
Quantization assigns a sampled signal to a discrete value from a finite set. The ADC's resolution, defined in bits (n), determines how close the quantized value is to the actual value, allowing for 2^n discrete levels. Resolution defines the minimum change in the input signal detectable by the ADC. Increasing the number of bits improves resolution.
The staircase-like transfer function of an ADC introduces quantization error, which is the difference between the actual and quantized values. This error can be defined in terms of LSB (Least Significant Bit); for example, 1 LSB. This error can be reduced by increasing the number of bits or by shifting the transfer function to reduce the error to 0.5 LSB.
Sampling involves taking discrete values of the analog signal at a particular rate. The Nyquist sampling theorem states that the sampling rate should be at least twice the maximum frequency of the input signal to accurately reconstruct it. If the sampling rate is too low, aliasing occurs, where the reconstructed signal's frequency is less than the original.
To prevent aliasing, particularly with signals like square waves that contain harmonics, an anti-aliasing filter (a low-pass filter) is used before sampling. Additionally, a sample-and-hold circuit is used to maintain a constant signal value during the ADC's quantization and encoding time, ensuring accurate conversion. The overall ADC block diagram includes these components.
For DACs, resolution, reference voltage, and settling time are important parameters; settling time dictates the maximum frequency that can be reconstructed. The video concludes by mentioning other critical parameters for both ADCs and DACs (gain/offset error, non-linearity, total harmonic distortion) and hints at exploring various ADC/DAC designs in future videos.