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Entry  Thu Mar 11 21:37:32 2010, Hao Huan, Input Bandwidth of the DRS Chip 
    Reply  Fri Mar 12 08:04:44 2010, Stefan Ritt, Input Bandwidth of the DRS Chip 
Message ID: 54     Entry time: Fri Mar 12 08:04:44 2010     In reply to: 53
Author: Stefan Ritt 
Subject: Input Bandwidth of the DRS Chip 

Hao Huan wrote:

I read in the DRS datasheet that the input bandwidth if 950MHz. However, it also says the output bandwidth in the transparent mode is 50MHz. Since in the transparent mode the input is routed to the output, does it mean the input bandwidth also gets reduced in the transparent mode? I don't know how the transparent mode works inside the chip of course, but this value would be important since if the hardware discriminators are connected to the output of DRS, we have to always work in the transparent mode.

In transparent mode, the input signal also gets routed to the output, where it goes through an output buffer, which limits the bandwidth to about 50 MHz, but only for the output. The effective bandwidth to the sampling cells is not changed. Please note however that the 950 MHz are for the "chip only". We measured this by keeping the input amplitude from a function generator constant at the input pin of the chip (measured with a high speed oscilloscope). Since each signal source has a non-zero impedance, the signal tends to "shrink" at high bandwidth, and we had to adjust the level of the function generator to keep the amplitude constant at high frequencies. If you do a realistic input stage with the THS4508 for example, the achievable bandwidth will be around 800 MHz.

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