LIMITERR - Limiter (Differential IO)
Model Kind
General
Model Sub-Kind
Generic Editor
SPICE Prefix
A
Model Name
LIMIT
SPICE Netlist Template Format
@DESIGNATOR %%vd(%1,%2) %%vd(%3,%4) @"DESIGNATOR"LIMIT
.MODEL @"DESIGNATOR"LIMIT limit (?in_offset|in_offset=@in_offset| ?gain|gain=@gain| ?out_lower_limit|out_lower_limit=@out_lower_limit| ?out_upper_limit|out_upper_limit=@out_upper_limit| ?limit_range|limit_range=@limit_range| ?fraction|fraction=@fraction|)
Parameters (definable at component level)
The following component-level parameters are definable for this model type and are listed on the Parameters tab of the Sim Model dialog. To access this dialog, simply double-click on the entry for the simulation model link in the Models region of the Component Properties dialog.
| In_Offset | input offset (Default = 0). |
| Gain | gain (Default = 1). |
| Out_Lower_Limit | output lower limit (Default = 0). |
| Out_Upper_Limit | output upper limit (Default = 1). |
| Limit_Range | upper and lower smoothing range (Default = 1.0e-6). |
| Fraction | used to control whether the is specified as a fractional (TRUE) or absolute (FALSE) value. (Default = FALSE). |
Notes
This model is similar in function to the Gain function. However, the output is restricted to the range specified by the output lower and upper limits. The input signal can be either a differential current or differential voltage signal.
This model is also similar in function to the Controlled Limiter, the difference being that the output limiting is defined using parameters of the model, rather than providing the limit levels external to the device.
The Limit_Range is the value below Out_Upper_Limit and above Out_Lower_Limit at which smoothing of the output begins. The Limit_Range therefore represents the delta, with respect to the output level, at which smoothing occurs. For example, for an input Gain of 2, Limit_Range of 0.1V and output limits of 1V (upper) and -1V (lower), the output will begin to smooth out at +/-0.9 V.
When the Limit_Range is specified as a fractional value (Fraction parameter set to TRUE), it is expressed as the calculated fraction of the difference between Out_Upper_Limit and Out_Lower_Limit.
Examples
Consider the limiter in the above image, with the following characteristics:
- Pin1 (positive input) is connected to net
In1 - Pin2 (negative input) is connected to net
In2 - Pin3 (positive output) is connected to net
Out - Pin4 (negative output) is connected to net
GND - Designator is
U1 - Gain =
3 - Out_Lower_Limit =
-15V - Out_Upper_Limit =
15V - All other model parameters are left at their inherent defaults.
The entry in the SPICE netlist would be:
*Schematic Netlist:
AU1 %vd(IN1,IN2) %vd(OUT,0) AU1LIMIT
.MODEL AU1LIMIT limit ( gain=3 out_lower_limit=-15 out_upper_limit=15 )
The effect of the function can be seen in the resultant waveforms obtained by running a transient analysis of the circuit.
In this example, the following analysis parameters on the Transient/Fourier Analysis page of the Analyses Setup dialog have been used:
- Transient Start Time - set to
0.000 - Transient Stop Time - set to
50.00m - Transient Step Time - set to
200.0u - Transient Max Step Time - set to
200.0u