Step 1: Circuit Overview
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The signals to be displayed enter on the left side. There are two input channels, their design is identical. First the signals get attenuated to make sure they do not exceed the range of the op-amp or the ADCs (0…5V). The attenuator has very high impedance and also acts as protection against excessive voltage at the inputs, together with the clamping diodes.
A low impedance divider provides some fixed offset to shift the input signal up, that way positive as well as negative voltages can be measured.
The signal then continues to the amplifier stage, consisting of two op-amps (both on the same physical op-amp chip). The first one acts as a simple unity gain buffer, the second stage provides 10x amplification.
Finally the signal enters the microcontroller where it gets digitized. The scope can change its voltage resolution by selecting which version of the signal to use – the one from the unit-gain buffer (for large input signals) or the 10x amplified version (for small signals).
The microcontroller captures the signal – the acquisition parameters (sample speed, voltage scaling, trigger setup come from the controlling PC) and sends the data back to the PC for display.
There is also a logic analyzer port – four digital inputs into the microcontroller.
Finally, the USB interface transmits data between microcontroller and PC and also provides power to the whole circuit.