---
# System prepended metadata

title: Recommended modification after beam test
tags: [Design, DeWei]

---

## Outline

* Modify the LED source so that its intensity is similar to beam test
* Bule Scintillater -> Green Scintillater
  * ~~1mm -> 2mm~~
    * ~~Aperture, F#~~
    	* Fiber Socket can't insert it
* Reverse bias of Photodiodes: **Maybe are not necessary**
  * Adjuster as the best dynamic range for us
* Why I need OP-AMP for photodiode?
* Input impedance of OP-AMPs
* Feasibility for 200 ohm *Rfb*
* Layout and design


## 1. Modify the LED source so that its intensity is similar to beam test

``` text
BNC_SRC -> R_LED -> LED -> BNC_GND
```
* R_LED: 1k ohm -> 10k ohm
* Rfb: 100M ohm 
* ![](https://i.imgur.com/doRIven.png)


## 2. Bule Scintillater -> Green Scintillater

* Blue Scintillater response on photodiode
  * ![](https://i.imgur.com/OQhnuKz.png)
* Green Scintillater response on photodiode
  * ![](https://i.imgur.com/vekVDPg.png)
* 2 times photo-current at least
* [DS of Scintillater](https://www.kuraray.com/uploads/5a717515df6f5/PR0150_psf01.pdf)
* [DS of PhotoDiode](https://www.farnell.com/datasheets/3029078.pdf)

## 3. Reverse bias of Photodiode: **Maybe is not necessary**

### 3.1 Testing about RevBias and Vo

* 0V
	* ![](https://i.imgur.com/8hQsf4l.png)
* -5V
	* ![](https://i.imgur.com/RT0pyqz.png)
* -11V
	* ![](https://i.imgur.com/oNaZJXp.png)

### 3.2 Summery of test

* Reversing bias would be better for *improve performance about freq(<< Cpd)*
	* Previous pratice: I need to add < -2.5V reverse bias if I'd like to see < 10us peak
* For our case (DC, F=0), Can't improve photocurrent
  * ![](https://i.imgur.com/t53XlSb.png)
  * Vrb >>, Ipd rised a little
* **Maybe we don't need reverse bias for photodiodes**
  * E = MC^2
    * M: More
    * C: Code
    * C: Component
  * Rigorously, we should do beam test again for verification 

## 4. Why I need OP-AMP for photodiode

* Refer to [here](https://hackmd.io/@pd-driver-ntuhep/BJI5AyJ12)

## 5. Input impedance of OP-AMPs

### 5.1 Let’s start with this question

* [OPA192: The output impedance is high, so is it suitable to as a unity-gain buffer?](https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/862563/opa192-the-output-impedance-is-high-so-is-it-suitable-to-as-a-unity-gain-buffer)
* [How is the output impedance of a closed loop opamp derived?](https://electronics.stackexchange.com/questions/510003/how-is-the-output-impedance-of-a-closed-loop-opamp-derived)
	* [Two-port network](https://en.wikipedia.org/wiki/Two-port_network)
	* [Op Amp Input Impedance](https://www.electronics-notes.com/articles/analogue_circuits/operational-amplifier-op-amp/input-impedance.php)

### 5.2 Analyze input impedance with non-ideal model of OP AMP(when f<<)

![](https://i.imgur.com/YRKRK0O.png)

### 5.3 Still not Believe that? see [here](https://www.ti.com/lit/ds/symlink/opa928.pdf)

## 6. Feasibility for 200 ohm *Rfb*

* **Flexibility issue**
* 100M ohm, AEC-Q200, 1% 
  * Footprint: 1206, 1210, 2012
* 200M ohm, AEC-Q200, 1% 
  * Footprint: only 2012 

## 7. Layout and design

* Replace potentiometer with fixed resistor
  * 100M/200M, see chapter 6
* Stack 5 board with copper rod
* Power/Signal I/O connector change to 90 deg type
* Split power from 1 board to 5 board and pi
  * Sould we need a split board?
* Can I Remove GPIOs of ADC?
  * Gain seletion
  * Trigger

![](https://imgur.com/qsewaus.png)