What is it?

This AD2 add-on opens up access to the AD2's differential input, as well as adds a low noise differential amplifier to detect ground plane shifts ( great for low level measurements as well)

Why did you make it?

To be able to verify ground plane integrity and make differential measurements. While I was working on a signal conditioner for Los Alamos National Labs, this functionality allowed me to find the root cause of a ground loop issue!

What makes it special?

This product lets you see the unseen, find the ground plane noise you were wondering about, measure small currents and find the noise levels of your LDO regulator.

It lets you take differential and single ended measurements at the normal voltage range, as well as 100X and 1000x amplification. It's like adding a microscope for electricity to your oscilloscope! This allows measurements from 25uV to 250v (with 10x probes).

It also lets you see the differential as well as a single ended trace simultaneously (without amplification, 1x probes).

It includes an adjustable low pass filter, so you can see DC effects without all the noise. Imagine being able to measure small currents even with small resistance shunts. With this device you can measure single milliamps across a short 22awg wire!

The AD2 is great because you have the convenience of everything (a scope, function generator, digital logic analyzer, network analyzer, etc.) all in one place. This product not only passes all these features through (including one existing differential input) but also adds the amplifier and analog filter. You can leave everything connected and change functionality with the flip of a switch.

The amplifier is Texas Instruments INA849. Some of the aspects that make this a great IC for the application include:

• Ultra-low noise: 1-nV/√Hz input voltage noise (typical) • Precision super-beta input performance: – Low offset voltage: 35 µV (maximum) – Low offset voltage drift: 0.4 μV/°C (maximum) – Low input bias current: 20 nA (maximum) – Low gain drift: 5 ppm/°C for G = 1 (maximum) • Bandwidth: 28 MHz (G = 1), 8 MHz (G = 100) • Slew rate: 35 V/µs • Common-mode rejection: 120 dB (minimum) for maximum gain

In this product the gain is set to 100 (the 1000x setting adds a second op amp), so the bandwidth is 8Mhz. This is fast enough to even work with digital logic applications.

The Analog Discovery 2 with this amplifier can make you an even greater electronics engineer or hobbyist, without needing the magical intuition that the seasoned guys seem to have.