Simulating Noise and Crosstalk problems with GEM detectors Matti Rahkala, HIP.

Part One Comparing of different Order Low Pass Filters. Smoothing High Voltage source output.

Frequency response of 1 to 4 Order RC-filters. Equal amount of the sum of Resistance and Capacitance

The same, but at Log scale times improvement (72 dB) at 1 MHz between 1. and 4. order filter

Impulse response. Equal V(t)*dt integrals. Decay time vs. Amplitude

Part two. Noise and Crosstalk simulation of the GEM Strips

Frequency response of the GEM Strips

Resistor – Capacitor contribution to The output Noise Level

Cont … Fighting against Noise 1. Detecting and attenuating the Common mode Noise Current 2. Forgotten enemy – microfonic phenomena. It needs furter investigations with a proper analysig tools. I propose use of Acceleration sensors and cross correlation measurement as an analytical tool. 3. Last but not least; Tribo electricity. Huge problem if ignored with measurement Setup. The Triboe effect is easy to demonstrate. It gives Huge noise response.

1. Power Supply Noise Common mode current coming from Power supply. Measured by toroidal current transformer. 2 mA pp (top trace) Corresponding Charge Amplifier output noise coupling. CM to normal mode Noise pick up. (Bottom trace)

HF-Noise envelope Before attenuation ferrites. Slow sweep, 8 mVpp Noise envelope at Amplifier output.

Sniffer tool. Simply toroidal transformer. 2 rounds secondary winding- 50 ohm termination.

Simply filter mVpp noise at output

Two rounds mVpp Noise Level

Three rounds. nine ferrites mVpp noise output

Some conclusions and Recommendations Don’t use switching power supplies if you can avoid it. CM-transformers (ferries) helps sometimes. CM- noise source impedance is too high for filters alone. Noise Current takes lowest impedance path to ground. The Art is: With Ferrites you can steer CM-noise Current to choose less hazardous path to the Ground. Ground Noise, You can’t attenuate it much but You can steer it to the harmless path!