# Regular Meeting (2023.2.13)
* Fanout-48
* Modify design: SMA -> test point
* Calculating Gain resistor
* Layout still doing

## Modify design: SMA -> test point
* Before
* 
* After
* 
* [The test point](https://www.mouser.tw/ProductDetail/Keystone-Electronics/5016?qs=qOqV1E1P08QbNAXL8l0G1A%3D%3D)
* Be used with probe
* 
* Although SMA(Coaxial) has better for noise rejecting, but test point is so convenient. Especially on the test stage.

## Calculating Gain resistor

* Last version(8 channels) I ignore that
* *Cm* and *Cd* of we used OPA
* 
* [2 port princeple](https://en.wikipedia.org/wiki/Two-port_network)
* Measure input capacitance -> output open
* 
* $Cm2 // (Cd + Cm1) = Cm2+\frac{(Cd)(Cm1)}{(Cd)+(Cm1)} = 16.7pF+\frac{(9.3pF)(16.7pF)}{(9.3pF)+(16.7pF)} = 22.674pF$
* 
* Assume Cin = 22.674pF, -3dB-freq = 28MHz
* 
* Rmax ~ 250 ohm
* Select commonly value: 220 ohm
* Power disssioation: Rg+Rf ~ 46 mW
* Simulation
* 
* 
* Lower Rfb or Rg will increase power dissipation
* $P=\frac{V^2}{R}$

###### tags: `Regular Meeting` `DeWei`