---
# System prepended metadata

title: Regular Meeting (2023.2.13)
tags: [Regular Meeting, DeWei]

---

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

## Modify design: SMA -> test point
* Before
  * ![](https://i.imgur.com/3AprUMR.png)
* After
  * ![](https://i.imgur.com/D5AptBY.png) 
* [The test point](https://www.mouser.tw/ProductDetail/Keystone-Electronics/5016?qs=qOqV1E1P08QbNAXL8l0G1A%3D%3D)
* Be used with probe
	* ![](https://i.imgur.com/xUu8hpE.png)
* 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
	* ![](https://i.imgur.com/BmLbY6v.png)
* [2 port princeple](https://en.wikipedia.org/wiki/Two-port_network)
* Measure input capacitance -> output open
	* ![](https://i.imgur.com/crSEUeB.png)
    * $Cm2 // (Cd + Cm1) = Cm2+\frac{(Cd)(Cm1)}{(Cd)+(Cm1)} = 16.7pF+\frac{(9.3pF)(16.7pF)}{(9.3pF)+(16.7pF)} = 22.674pF$
      * ![](https://i.imgur.com/tuprC78.png)	
* Assume Cin = 22.674pF, -3dB-freq = 28MHz
  * ![](https://i.imgur.com/UPNZnfp.png)	
  * Rmax ~ 250 ohm
    * Select commonly value: 220 ohm
    * Power disssioation: Rg+Rf ~ 46 mW
* Simulation
  * ![](https://i.imgur.com/HP9jsze.png)
  * ![](https://i.imgur.com/oN8Waf4.png)
* Lower Rfb or Rg will increase power dissipation
  * $P=\frac{V^2}{R}$

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