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What Happened Yesterday

What Happened Yesterday. Mihir Ravel *Voltage tolerance of the peak-and-hold is 1.5-4.2 V; use gain and offset *What’s the bandwidth of our peak-and-hold? We’ll measure this (worrying only about the high frequency end), but it’s likely less than 100 ns

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What Happened Yesterday

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  1. What Happened Yesterday Mihir Ravel *Voltage tolerance of the peak-and-hold is 1.5-4.2 V; use gain and offset *What’s the bandwidth of our peak-and-hold? We’ll measure this (worrying only about the high frequency end), but it’s likely less than 100 ns *When do we pull the value from the peak-and-hold? Make this software-controlled, taking a fixed amount of time Steve Holt *ADC speed does not necessarily depend on clock speed; GHz crystal not needed

  2. Signal Shape • Quick rise time w/ slow decay time • Impulse response of peak-and-hold circuit is first-order; exponential decay • …Implement a fixed delay from peak to ADC sampling? 1 μs 2 μs

  3. All X-ray pulses have this characteristic fast-rise, slow-decay shape. That means a higher pulse, despite having a longer wait-period to ADC conversion, will still be detected as a higher voltage.

  4. When to sample from the peak-and-hold? New Method 1) Comparator detects threshold crossing; start waiting using trigger-event on comparator’s rising edge 2) Wait for a fixed, user-controlled amount of time using firmware counter; enable A/D 3) Data read after maximum A/D time (or query and loop)4) Reset the comparator • Old Method • Sample once the signal goes below threshold • Find this point using comparator/latch

  5. Additional Tasks • Begin documentation. Discuss the signals that the MCA is going to be detecting. Note their Poisson distribution. Describe the signals as impulses w/ fast rise-time and slow decay. Also, talk about the portability of the MCA for a variety of detectors. Note the rise-time is dependent on detector type. • Look up peripheral devices that support high-speed USB such as RISC or CPLDs *System architecture layout w/ interfaces *Detailed timing diagram w/ labels and estimated times

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