2.11 DC command
2.11.1 Syntax
dc start stop stepsize {options ...}
dc label start stop stepsize {options ...}
2.11.2 Purpose
Performs a nonlinear DC steady state analysis, and sweeps the signal input,
or a component value.
2.11.3 Comments
The nodes to look at must have been previously selected by the print or
plot command.
If there are numeric arguments, without a part label, they represent a ramp
from the generator function. They are the start value, stop value
and step size, in order. They are saved between commands, so no arguments
will repeat the previous sweep.
A single parameter represents a single input voltage. Two parameters
instruct the computer to analyze for those two points only.
In some cases, you will get one more step outside the specified range of
inputs due to internal rounding errors. The last input may be beyond the end
point.
This command also sets up a movable operating point for subsequent AC
analysis, which can be helpful in distortion analysis.
The program will sweep any simple component, including resistors,
capacitors, and controlled sources. SPICE sweeps only fixed sources (types
V and I).
This command will sweep up to 4 components, nested.
2.11.4 Options
- * multiplier
-
Log sweep. Multiply the input by multiplier to get the next
step. Do not pass zero volts!!
- > file
-
Send results of analysis to file.
- >> file
-
Append results to file.
- by stepsize
-
Linear sweep. Add stepsize to get the next step.
- continue
-
Use the last step of a OP, DC or Transient analysis
as the first guess.
- decade steps
-
Log sweep. Use steps steps per decade.
- dtemp degrees
-
Temperature offset, degrees C. Add this number to the temperature
from the options command.
- loop
-
Repeat the sweep, backwards.
bb
- noplot
-
Suppress plotting.
- plot
-
Graphic output, when plotting is normally off.
- quiet
-
Suppress console output.
- reverse
-
Sweep in the opposite direction.
- temperature degrees
-
Temperature, degrees C.
- times multiplier
-
Log sweep. Multiply the input by multiplier to get the next
step. Do not pass zero volts!!
- trace n
-
Show extended information during solution.
Must be followed by one of the following:
-
off
- No extended trace information (default, override .opt)
- warnings
- Show extended warnings
- iterations
- Show every iteration.
- verbose
- Show extended diagnostics.
2.11.5 Examples
- dc 1
- Do a single point DC signal simulation, with `1 volt'
input.
- dc -10 15 1
- Sweep the circuit input from -10 to +15 in steps of
1. (usually volts.) Do a DC transfer simulation at each step.
- dc
- With no parameters, it uses the same ones as the last time.
In this case, from -10 to 15 in 1 volt steps.
- dc 20 0 -2
- You can sweep downward, by asking for a negative
increment. Sometimes, this will result in better convergence, or even
different results! (For example, in the case of a bi-stable circuit.)
- dc
- Since the last time used the input option, go back one
more to find what the sweep parameters were. In this case, downward from 20
to 0 in steps of 2. (Because we did it 2 commands ago.)
- dc -2 2 .1 loop
- After the sweep, do it again in the opposite
direction. In this case, the sweep is -2 to +2 in steps of .1. After it
gets to +2, it will go back, and sweep from +2 to -2 in steps of -.1. The
plot will be superimposed on the up sweep. This way, you can see hysteresis
in the circuit.
- dc temperature 75
- Simulate at 75 degrees, this time. Since we
didn't specify new sweep parameters, do the same as last time. (Without the
loop.)