Feature: Software & Tools


Figure 1: Simulated output noise and each resistor’s noise contribution


for each case against the most dominant thermal noise (R3 at 100nV/√Hz) added by the amplifier. For example, for Case 1 the sample added noise is 0.1pA/√Hz. Looking at Tables 1 and 2, it can be


concluded that keeping the added noise at or below 3dB requires input current noise of over 1pA/√Hz and input voltage noise of above 7nV/√Hz. A device such as the Analog Devices AD8055 with 1pA/√Hz


and 6nV/√Hz noise fits the bill here, and when simulated has a broadband noise of 144nV/√Hz, close to the predicted noise from Tables 1 and 2. In summary, we can easily see from


Figure 2: UniversalOpAmp versions www.electronicsworld.co.uk September 2023 31


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