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Homework Help: Selecting a Transistor for Sample and Hold Circuit

  1. Nov 10, 2013 #1
    This is my first time here on this forum. I am building an analog to digital converter. It will be running at a frequency of 12MHz and the sample and hold circuit will be 1/8th of that or 1.5MHz. This will be an 8-bit converter and Vdd will be 5 volts. I have a few parts to workout, the sample and hold circuit, comparator, and connectors to the analog input and digital output. I need to select transistors for the sample and hold circuit. I'd just like some help on how to select a transistor for my project. Below is a photo of the circuit I plan to use. The switch will be a transmission gate CMOS switch. I need to find a transistor for this switch with low capacitance in the right place. Also, need several more transistors for the amplifiers. Since, I plan to use these transistors on both a breadboard and PCB, I'll need one that's available in both through hole and SMD types. There are so many transistors to choose from that I don't know if I can find better than whatever one I find. I hope you guys can point me in the right direction to finding one via Mouser or Digikey.

    I hope to use this circuit for actual projects in the future. The particular design I choose for this was for the speed, low power dissipation, wide bandwidth, high input impediance, and low output impediance.

    Thank you in advance for your help,
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
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