# Introduction 

One of the most important stages during circuit design is simulation. Several circuit simulators are available to carry out the task, but SPICE-based simulators are the most versatile and powerful.

SPICE stands for Simulation Program with Integrated Circuit Emphasis. It is a general-purpose, open-source analog electronic circuit simulator originally developed at the University of California, Berkeley, in the 1970s. SPICE is now the foundation for almost all modern circuit simulators (like LTspice, PSpice, HSPICE, Ngspice, etc.).

# The basic PCG Scheme

![The PCG general scheme](./block-scheme.jpg)


# Non-inverting amplifier
## Design equations
The Operational amplifier design is based on:
- No feedback


## Simulation with UI

![The PCG general scheme](./non-inverter.jpg)

## Simulation with code
```
* Non-inverting amplifier with UniversalOpamp2
Vin in 0 SINE(0 1 1k)
R3  in vp 100k
R1  vn out 470k
R2  vn 0  1k
R4  out 0 100k

* Library (comes with LTspice) and instance
.include opamp.sub
XU1 vp vn out opamp Aol=100k GBW=10Meg

.tran 0 1m 0 0.1u
.end
```





```spice
Version 4
SymbolType CELL
LINE Normal -32 32 32 64
LINE Normal -32 96 32 64
LINE Normal -32 32 -32 96
LINE Normal -28 48 -20 48
LINE Normal -28 80 -20 80
LINE Normal -24 84 -24 76
WINDOW 0 0 32 Left 2
SYMATTR Prefix X
SYMATTR Description Ideal single-pole operational amplifier. You must .lib opamp.sub
SYMATTR Value opamp
SYMATTR SpiceLine Aol=100K
SYMATTR SpiceLine2 GBW=10Meg
PIN -32 48 NONE 0
PINATTR PinName invin
PINATTR SpiceOrder 1
PIN -32 80 NONE 0
PINATTR PinName noninvin
PINATTR SpiceOrder 2
PIN 32 64 NONE 0
PINATTR PinName out
PINATTR SpiceOrder 3
```