Scope front ends

Preamble

Leading on from Miniscope, I wondered if I should/could improve on the front end of the STM32F103C8T6 board based scope which connects to A0 and A1

Featured image from EEVblog #37 – Rigol DS1052E Oscilloscope Teardown

Teardown links

Rigol-DS1054Z-Schematic-FrontEnd.png

Back to the Miniscope

The Miniscope uses a relatively simple front end:

An interesting article is Scope front ends

Two TI PDFs Texas Instruments LMH6518 900 MHz, Digitally Controlled, Variable Gain Amplifier and 50-Ohm 2-GHz Oscilloscope Front-end Reference Design PDFs: lmh6518 and 50-Ohm 2-GHz Oscilloscope Front-end Reference Design

Protection

From ESE498 4-Channel USB Audio Oscilloscope by Samuel Powell and Michael Steinbock PDF: ESE498 4-Channel USB Audio Oscilloscope

4.1 Input Stage: Protection and Coupling

The input connectors for each channel are standard female BNC jacks. The signal line of each is connected to ground via a Transient Voltage Suppressor (TVS) diode nominally rated to protect for voltages 48V above or below ground. (The minimum and maximum breakdown voltages of the TVS diode are 53.3V and 558.9V, respectively.) If an overvoltage condition occurs on the input, these diodes will short to ground and dissipate any power that could damage components down the line. Following the TVS diode on each channel is an AC coupling capacitor and a jumper used to switch between AC and DC coupling. The AC coupling capacitor is rated for 200V. It has a value of 0.1µF, which combined with the 1MΩ nominal input impedance of the vertical scaling stage forms a high-pass filter with a cutoff frequency of 1.59Hz. A schematic of this stage is shown below in Figure 5 on page 7.

Oscilloscope front stage schematic - Protection

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