An analog-to-digital converter (ADC) is an integrated circuit that converts analog input signals into digital representations. Understanding ADC operation is essential for sensor signal interpretation and ECU tuning.

ADC Fundamentals#

Bit Resolution#

The bit resolution of an ADC determines how many discrete values it can represent. An 8-bit ADC produces 2^8 = 256 possible output values (0–255).

Calculation:

• 2^8 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 = 256 values
• Range: 0 to 255 (zero is a valid state)

Reference Voltage#

The reference voltage (Vref) is the maximum analog input that corresponds to full-scale digital output. A common reference voltage in automotive ECUs is 5.00V.

Example:

• If Vref = 5.00V and the input signal = 5.00V, the output = 255 (full scale)
• If the input signal = 0V, the output = 0

Conversion Formula#

The digital output is calculated as:

Digital Output = ((Vin / Vref) × 2^number of bits) − 1

Where:

• Vin = Input analog voltage
• Vref = Reference voltage
• Number of bits = ADC resolution (e.g., 8, 10, 12 bits)

This formula allows precise prediction of the digital value the ECU will read for any given input signal.

Resolution and Accuracy#

Important

Analog-to-digital conversion is inherently an approximation process. Each discrete digital value must represent a range of analog values, not a single point.

Resolution (measured in bits) defines how finely the ADC divides the analog input range:

• Higher bit resolution = Smaller steps between values = Greater precision
• Lower bit resolution = Larger steps between values = Lower precision

For example, an 8-bit ADC with a 5.00V reference has a step size (least significant bit, or LSB) of:

• LSB = Vref / 2^bits = 5.00V / 256 ≈ 0.0195V per step

An 10-bit ADC with the same 5.00V reference provides finer resolution:

• LSB = 5.00V / 1024 ≈ 0.00488V per step