* Question
What are the main technical indicators of A/D conversion?
* Answer
The main technical indicators of A/D (Analog-to-Digital) conversion define how accurately and efficiently an analog signal is converted into its digital representation. These indicators are crucial for selecting and evaluating ADCs (Analog-to-Digital Converters) in applications like instrumentation, control systems, audio processing, and data acquisition.
1. Resolution
Definition: The number of bits used to represent the analog input.
Significance: Determines how many discrete digital values the ADC can output.
Example: A 12-bit ADC provides 212= 4096 levels.
Impact: Higher resolution = finer granularity = better precision.
2. Sampling Rate (Sampling Frequency, fs)
Definition: Number of samples taken per second, measured in samples per second (S/s or Hz).
Significance: Affects the bandwidth and ability to track fast signal changes.
Nyquist Criterion: Must be at least twice the highest input frequency to avoid aliasing.
3. Input Range
Definition: The minimum and maximum voltage levels the ADC can measure (e.g., 0–5 V).
Impact: Input signals outside this range may be clipped or distorted.
4. Signal-to-Noise Ratio (SNR)
Definition: Ratio of the signal power to the noise power, usually expressed in dB.
Formula (ideal ADC):
SNR=6.02N+1.76 dB
where N is the number of bits.
Higher SNR indicates cleaner signal with less quantization or thermal noise.
5. Effective Number of Bits (ENOB)
Definition: The actual number of usable bits, accounting for all real-world imperfections.
Significance: Reflects real resolution in presence of noise and non-linearity.
6. Total Harmonic Distortion (THD)
Definition: Measure of distortion introduced by harmonics in the digital output.
Expressed in: dB or percent (%).
Lower THD = better fidelity, especially for audio and RF applications.
7. Integral Non-Linearity (INL)
Definition: The deviation between actual and ideal ADC transfer function across the full range.
Measured in: Least Significant Bits (LSBs).
Impact: Affects absolute accuracy of conversion.
8. Differential Non-Linearity (DNL)
Definition: Difference between actual and ideal step size between adjacent codes.
Key Risk: If DNL > 1 LSB, ADC may be non-monotonic (output can decrease when input increases).
9. Conversion Time / Latency
Definition: Time taken for the ADC to convert an analog input to a digital output.
Relevant in: Real-time control and high-speed acquisition systems.
10. Power Consumption
Important in: Battery-powered or thermally constrained systems.
Depends on: Resolution, sampling rate, and architecture (e.g., SAR vs. Sigma-Delta).
Summary Table
Indicator | Description | Unit |
Resolution | Number of bits used in conversion | bits |
Sampling Rate | Samples per second | Hz / S/s |
Input Range | Voltage span accepted | Volts (V) |
SNR | Signal vs. noise power | dB |
ENOB | Effective usable bits in real-world conditions | bits |
INL / DNL | Linearity error metrics | LSB |
THD | Harmonic distortion | dB or % |
Conversion Time | Delay between input and output | µs / ns |
Power Consumption | Energy used per operation | mW / µW |
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