# Analog Spiking Neuron Circuit and 10-bit Digital to Analog Converter - Caravel Submission 

## Analog Spiking Neuron Circuit

This is the Google/EFabless/Skywater Caravel submission of an [Analog Spiking Neuron Circuit.](https://ieeexplore.ieee.org/document/9184447) The submission also includes a SONOS transistor array. 

### Neuron circuit
The circuit in the original paper is in 130nm technology and has a vdd of 300mV. Skywater pdk is hybrid 180nm/130nm node where the minimum transistor length is 150nm.
As a result vdd needs to be higher in order to get the circuit to work properly. In simulation 700mV seems to work well. 

<p align=”center”>
<img src="/doc/neuron.png" width="75%"> 
</p>

#### Pinout
| node   | pad         | node      | pad         |
|--------|-------------|-----------|-------------|
| i_bias | mprj_io[13]  | v_buff    | mprj_io[22] |
| vad    | mprj_io[14]  | u_buff    | mprj_io[23] |
| vr     | mprj_io[15]  | a_buff    | mprj_io[24] |
| vk     | mprj_io[16] | axon_buff | mprj_io[25] |
| vth    | mprj_io[17] | sel       | mprj_io[26] |
| vw     | mprj_io[18] | v_syn     | mprj_io[27] |
| vau    | mprj_io[19] | u_syn     | mprj_io[28] |
| vsyn0  | mprj_io[20] | a_syn     | mprj_io[29] |
| vsyn1  | mprj_io[21] | axon_syn  | mprj_io[30] |
|        |             | i_in      | mprj_io[31] |

#### Extracted Netlist Simulation 
Spiking pattern at v_buff for i_in = 10pA DC 
<p align=”center”>
<img src="/doc/sample_sim.png" width="75%"> 
</p>

### SONOS array
A 2x2 array of nfet sonos cells with transistor sizing 420nmx150nm.
<p align=”center”>
<img src="/doc/sonos.png" width="75%"> 
</p>

#### Pinout
| node | pad         |
|------|-------------|
| WL0  | mprj_io[7]  |
| WL1  | mprj_io[8]  |
| BL0  | mprj_io[9]  |
| SL0  | mprj_io[10] |
| BL1  | mprj_io[11] |
| SL1  | mprj_io[12] |


## 10-bit Digital to Analog Converter

The mega project area also contains a 10-bit Potentiometric Digital to Analog Converter built off of [Ashutosh Sharma's design.](https://github.com/xzlashutosh/avsddac_3v3) The design uses a 3.3V rail voltage, and 1.8V digital input voltage. The DAC's inputs are controlled by the Caravel harness' built in RISC-V core. [Ashutosh Sharma's design](https://github.com/xzlashutosh/avsddac_3v3) used the OSU180 process, for the caravel submission it was ported to the Sky130 process. 

The design uses a string of polysilicon resistors in series to create a string DAC. The resistors are connected to digital switches in order to achieve an exact voltage at the output. The device was built through hierarchical sub-circuits and sub-layouts starting off at 2-bit, then 3-bit and so forth, incrementally reaching 10-bit. With a full scale of 3.3 V and a 10 bit resolution. 

## Pinout

| Node          | Pad           |
| :------------ | ------------- |
| Analog_Out    | analog_io[25] |
| Digital_In[0] | io_in[0]      |
| Digital_In[1] | io_in[1]      |
| Digital_In[2] | io_in[2]      |
| Digital_In[3] | io_in[3]      |
| Digital_In[4] | io_in[4]      |
| Digital_In[5] | io_in[5]      |
| Digital_In[6] | io_in[6]      |
| Digital_In[7] | io_in[7]      |
| Digital_In[8] | io_in[8]      |
| Digital_In[9] | io_in[9]      |
| VDD           | vdda1         |
| Gnd           | vssa1         |

#### Simplified DAC Architecture 
String of resistors and switches that make up potentiometric DAC.
<p align=”center”>
<img src="/doc/circuit_DAC.png" width="45%"> 
</p>

#### Abstracted DAC Block Diagram 
Simple block representing all inputs and outputs of DAC.
<p align=”center”>
<img src="/doc/abstract_block_diagram.png" width="45%"> 
</p>

# Installation

To setup and install the repo for development:

1. Install prerequisite tools:
   1. Install [Magic VLSI Layout Tool](http://opencircuitdesign.com/magic/)
      - Note: As of 12/7/2020 you must install Magic from source code. The packaged version will not work with OpenPDKS.
   2. Install [KLayout](https://www.klayout.de/build.html)
   3. Install [SkywaterPDK](https://github.com/google/skywater-pdk) and [OpenPDK](https://github.com/RTimothyEdwards/open_pdks) using [OpenLane](https://github.com/efabless/openlane.git)
      1. Clone and Install OpenLane. This will also grab and install SkywaterPDK and OpenPDK for you:

```shell
export PDK_ROOT=(where pdks will be installed)

cd $PDK_ROOT

git clone https://github.com/efabless/openlane.git -b mpw-one-a

cd openlane
export OPENLANE_ROOT=$(pwd)
make
```

​			2. Clone and uncompress the repo:

```shell
git clone https://github.com/Bryce-Readyhough/caravel_UNCC_MPW_1.git
make uncompress -j$nproc
```