Voltage Source

Voltage Source #

Provides various voltage and current waveforms for circuit simulation. From simple DC supplies to complex modulated signals, Breadpad’s sources enable comprehensive circuit testing.

Basic Properties #

  • Terminals: 4 tie points (2x2 grid)
  • SPICE Designation: V (voltage) or I (current)
  • Layout: Rows 7-8, occupies 2 columns
  • Connection: All 4 tie points internally connected

Source Types #

DC Source (Default) #

  • Parameters: Voltage/Current value
  • Tolerance: Optional variation for Monte Carlo
  • Applications: Power supplies, bias, references

AC Source (Sine Wave) #

  • Amplitude: Peak voltage/current
  • Frequency: Hz, kHz, MHz, GHz
  • Phase: Initial phase in degrees
  • Delay: Time before sine starts
  • Damping Factor: Exponential decay
  • Applications: Signal generators, AC analysis

PWM/PULSE Source (Premium) #

  • Amplitude: High level value
  • Delay: Initial delay time
  • Rise Time: 0% to 100% transition
  • Fall Time: 100% to 0% transition
  • Pulse Width: High state duration
  • Period: Total cycle time
  • Applications: Digital circuits, PWM control

EXP Source (Exponential) (Premium) #

  • Amplitude: Peak value
  • Rise Delay: Time before rise
  • Rise Time Constant: Rise exponential τ1
  • Fall Delay: Time before fall
  • Fall Time Constant: Fall exponential τ2
  • Applications: Transient testing, charge/discharge

PWL Source (Piecewise Linear) (Premium) #

  • Time-Value Pairs: Arbitrary waveform
  • Linear Interpolation: Between points
  • Applications: Custom waveforms, data replay

SFFM Source (FM Modulation) (Premium) #

  • Carrier Amplitude: Carrier signal level
  • Carrier Frequency: Base frequency
  • Modulation Index: Frequency deviation
  • Modulation Frequency: Modulating signal
  • Carrier Phase: Initial carrier phase
  • Signal Phase: Modulation phase
  • Applications: Communications, FM testing

AM Source (AM Modulation) (Premium) #

  • Carrier Amplitude: Unmodulated level
  • Carrier Frequency: Carrier frequency
  • Modulation Frequency: Envelope frequency
  • Modulation Depth: 0-1 (0-100%)
  • Delay: Start delay
  • Phase: Carrier phase offset
  • Applications: RF circuits, AM radio

SPICE Netlist Examples #

DC Source #

V1 1 0 DC 5
V2 2 0 DC 3.3 AC 1   ; DC with AC component

DC with Tolerance #

V1 1 0 DC {5*(1+gauss(0,0.05/3,6))}  ; 5% tolerance

AC Source #

V1 1 0 SIN(0 1 1k 0 0 0)  ; 1V 1kHz sine
* SIN(offset amplitude freq delay damping phase)

Pulse Source #

V1 1 0 PULSE(0 5 1n 1n 1n 50n 100n)
* PULSE(V1 V2 delay rise fall width period)

PWL Source #

V1 1 0 PWL(0 0 1m 5 2m 5 3m 0)
* Time-voltage pairs

Current Sources #

I1 0 1 DC 10m      ; 10mA into node 1
I2 0 2 SIN(0 1m 1k) ; 1mA sine current

Common Power Supply Values #

Digital Logic #

  • 5V TTL: 5.0V ± 5%
  • 3.3V Logic: 3.3V ± 5%
  • 1.8V Core: 1.8V ± 3%
  • 1.2V DDR: 1.2V ± 3%

Analog Circuits #

  • ±15V Op-Amps: Dual supplies
  • ±12V Audio: Standard audio rails
  • ±5V: Portable/USB powered
  • 9V Battery: 9V nominal, 7-9.6V range

Power Electronics #

  • 12V Automotive: 11-14.5V range
  • 24V Industrial: 22-26V range
  • 48V Telecom: -48V standard
  • Line Voltage: 120V/240V AC (use carefully)

Signal Generation Tips #

Test Signals #

* 1kHz test tone
VTEST 1 0 SIN(0 1 1k)

* Square wave (using PULSE)
VSQUARE 1 0 PULSE(-1 1 0 1n 1n 0.5m 1m)

* Triangle wave (using PWL)
VTRI 1 0 PWL(0 0 0.25m 1 0.5m 0 0.75m -1 1m 0) R

* Sweep (using PWL)
VSWEEP 1 0 PWL(0 0 1 10) ; 0-10V over 1 second

Digital Clocks #

* 10MHz clock, 50% duty cycle
VCLK 1 0 PULSE(0 3.3 0 0.1n 0.1n 50n 100n)

* Clock with jitter (Monte Carlo)
VCLK 1 0 PULSE(0 5 {gauss(0,1n,3)} 1n 1n 50n 100n)

Modulated Signals #

* AM: 1MHz carrier, 1kHz modulation, 50% depth
VAM 1 0 AM(1 1 1e3 1e6 0.5 0 0)

* FM: 100MHz carrier, 10kHz deviation
VFM 1 0 SFFM(1 100e6 10e3 1e3 0 0)

Source Impedance #

Ideal sources have:

  • Voltage source: 0Ω output impedance
  • Current source: ∞Ω output impedance

For realistic sources, add series/parallel resistance:

* 50Ω source impedance
V1 1 0 SIN(0 1 1k)
RS 1 2 50

* Current source with parallel resistance
I1 0 1 DC 1m
RP 1 0 10k

Power Calculations #

SPICE can measure source power:

.PROBE
.PRINT DC V(1) I(V1) P(V1)
.PRINT AC VM(1) IM(V1) PM(V1)

Design Considerations #

Startup Behavior #

  • Use PULSE with delay for sequenced startup
  • PWL for controlled ramp-up
  • .IC for initial conditions

Load Regulation #

  • Add series resistance for realistic supplies
  • Use .STEP to vary load current
  • Check voltage under min/max load

Noise and Ripple #

  • Add AC component to DC sources
  • Use multiple sine waves for harmonics
  • Consider NOISE analysis

Protection #

  • Real supplies need current limiting
  • Add clamp diodes for overvoltage
  • Include fuses in high-power circuits

Simulation Tips #

  1. Convergence: Start with DC, add complexity
  2. Time Steps: PULSE rise/fall > 0 for convergence
  3. PWL Points: More points = smoother curves
  4. AC Analysis: Needs AC 1 specification
  5. Monte Carlo: Use tolerance for variations
  6. Multiple Sources: Mind the grounds!

See Also #