While calculating the inherent offset voltage of a device often involves complex internal parameters or direct measurement, a key aspect of understanding offset voltage is calculating its impact on the output voltage of a circuit. The provided reference explains precisely how to calculate the total output voltage when offset voltage is present alongside the input signal.
Calculating Output Voltage with Offset
The offset voltage is an undesirable DC voltage that appears at the output of an amplifier (or referred back to the input) even when no external input signal is applied. When an input signal is applied, this offset voltage effectively adds to the desired signal before amplification.
According to the provided reference:
The total output voltage is the series combination of the offset and the input signal (1mV + 0.1mV), multiplied by the gain (100), which gives us 110 mV. The offset accounts for about 10% error.
This statement shows the calculation for the total output voltage:
- Identify the Input Signal Voltage: The desired voltage you are trying to amplify (e.g., 1mV).
- Identify the Offset Voltage: The inherent error voltage (e.g., 0.1mV).
- Identify the Gain: The factor by which the amplifier increases the combined input (e.g., 100).
- Sum the Input and Offset: Add the input signal voltage and the offset voltage together.
- Multiply by Gain: Multiply the sum by the amplifier's gain to get the total output voltage.
Calculation Steps:
- Sum of Inputs:
Input Signal Voltage + Offset Voltage - Total Output:
(Input Signal Voltage + Offset Voltage) * Gain
Example from Reference:
- Input Signal Voltage = 1mV
- Offset Voltage = 0.1mV
- Gain = 100
Total Output Voltage = (1mV + 0.1mV) 100
Total Output Voltage = (1.1mV) 100
Total Output Voltage = 110mV
The Impact of Offset
As highlighted in the reference, even a small offset voltage can introduce significant error, especially with high gain. In the example, the 0.1mV offset, amplified by 100, contributes 10mV to the output, making the 100mV signal (1mV * 100) become 110mV. This extra 10mV represents a 10% error relative to the ideal 100mV output signal.
Understanding this calculation is crucial for analyzing circuit performance and error sources. While the reference shows how offset voltage influences the output calculation, determining the offset voltage value itself typically requires consulting datasheets for typical/maximum values or performing measurements on the specific device. Offset drift over temperature can also be calculated similarly by determining the offset voltage at different temperatures.
