marc.pirello@LIGO.ORG - posted 17:01, Monday 08 August 2016 - last comment - 14:33, Tuesday 04 October 2016(28939)
PI Correction in HV for ETM ESD Driver - Function Analysis
ECR E1600230-v1
WP 6053
We analyzed the transfer function through the ETM ESD Driver before and after the capacitor and TVS were applied (see ECR). Using the Dynamic Signal Analyzer (SR785) set to sweep from 1kHz to 100kHz at 1000mV, the driver performs as expected when the waveform is applied to the PI input. I have attached a plot of the transfer function displaying modified HV, modified LV, and pre-mod HV values.
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For future reference, this transfer function was taken from the differential PI input (pins 1/9 or 2/10 of the DB15 connector on the bottom of pg 1 in D1500016) on the front of the chassis to the BNC output inside the chassis itself (P5, P6, P9, or P10 in the middle of pg 1 in D1500016). The AC gain of this path is nominally 2.0, or +6 dB (G = 1 + R28/R30 on pg 6 of D1500016), but what mark shows here is that the gain changes by ~2 dB when the high voltage path is engaged. Also, the capacitor is 1 [nF] as quoted from the ECR. However, given the components surrounding this cap, I can't really figure out why the pole frequency is at 10 kHz. The input impedance to the relay (pg 8 of D1500016) is 200 [Ohm] from the summing node (pg 9 of D1500016). Thus, I would guess that the pole frequency would be at 1/(2 * pi * 200 [Ohm] * 1e-9 [F]) = 0.79 [MHz], not 10 [kHz]. One would need a resistance of ~15 [kOhm] to bring the pole frequency down to 1/(2 * pi * 1.5e4 [Ohm] * 1e-9 [F]) = 10.6 [kHz]. Because the pole frequency doesn't change, regardless of the relay state, it implies some other resistance to ground some where... Eh well. Measurements don't lie -- 10 [kHz] it is!