Selecting a Transistor for a Sample and Hold Circuit

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,
Mike

It would be unusual in this day and age to build this circuit using discrete components. A CMOS switch, such as a DG211, is commonly used.

If you do build it using discrete MOSFETs, small (relatively high Rds ON) logic level parts would be good. A quick check at Digikey shows these to possibly be suitable:

ON Semiconductor 3LP01M-TL-H (P-channel)
ON Semiconductor NTA7002NT1G (N-channel)

You will have to analyze the circuit with these parts, or simulate it, to see if these are fast enough and the power consumption is low enough.

I would not use a voltage amplifier after the sample and hold capacitor. A follower (gain-of-1) circuit could be better as you don't want to amplify the error introduced by charge injection into the capacitor.