Simulating Noise and Crosstalk problems with GEM detectors

Matti Rahkala, HIP.

Part OneComparing 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

Frequency

100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHzV(Out4) V(Out3) V(Out2) V(Out1)

0V

0.2V

0.4V

0.6V

0.8V

1.0V

The same, but at Log scale. 3800 times improvement (72 dB) at 1 MHz between 1. and 4. order filter

Frequency

100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHzV(Out4) V(Out3) V(Out2) V(Out1)

1.0nV

1.0uV

1.0mV

1.0V

10pV

10V

(1.0000M,1.5916m)

(1.0000M,417.920n)

4. Order filter

1. Order Filter

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

Time

0s 50us 100us 150us 200us 250us 300us 350us 400usV(Out4) V(Out3) V(Out2) V(Out1)

0V

0.5V

1.0V

1.5V

1. Order

2. Order

3. Order

4. Order

Part two. Noise and Crosstalk simulation of the GEM Strips

Frequency response of the GEM Strips

Frequency

1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHzV(B3) V(B2) V(B1) V(In) V(Out)

1.0pV

10nV

100uV

1.0V

1.0KV

3. adjacent Strip

2. adjacent Strip

First adjacent Strip Voltage

Strip Voltage

Output

Resistor – Capacitor contribution to The output Noise Level

Frequency

1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz1 SQRT(S(NTOT(ONOISE))) 2 V(ONOISE)

0

0.5m

1.0m

1.5m1

0V

20uV

40uV

60uV

80uV2

>>

1.428 mV RMS

RMS Output total noise as fuction of upper FrequencyOutput Noise density, V/SQRT(Hz)

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. 1.64 mVpp noise at output

Two rounds

1.593 mVppNoise Level

Three rounds. nine ferrites.

1.050 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!