CLIMITER - Controlled Limiter (Single-Ended IO)

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Model Kind

General

Model Sub-Kind

Generic Editor

SPICE Prefix

A

Model Name

CLIMIT

SPICE Netlist Template Format

@DESIGNATOR %1 %2 %3 %4 @"DESIGNATOR"CLIMIT
.MODEL @"DESIGNATOR"CLIMIT climit (?in_offset|in_offset=@in_offset| ?gain|gain=@gain| ?upper_delta|upper_delta=@upper_delta| ?lower_delta|lower_delta=@lower_delta| ?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).

Upper_Delta

output upper delta (Default = 0).

Lower_Delta

output lower delta (Default = 0).

Limit_Range

upper and lower smoothing range (Default = 1.0e-6).

Fraction

used to control whether the limit range 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 (cntl_lower and cntl_upper pins of the device). The input signal can be either a single-ended current or single-ended voltage signal.

The Limit_Range is the value below the cntl_upper limit and above the cntl_lower limit at which smoothing of the output begins. A minimum positive value of current/voltage must exist between the cntl_upper and cntl_lower inputs, at all times. 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 (on pin cntl_upper) and -1V (on pin cntl_lower), the output will begin to smooth out at +/-0.9 V.

The input values arriving at the cntl_upper and cntl_lower pins of the device are tested to verify that they are far enough apart to guarantee a linear range between them. The range is calculated as:

(cntl_upper - Upper_Delta - Limit_Range) - (cntl_lower + Lower_Delta + Limit_Range)

and must be greater than or equal to zero.

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 cntl_upper and cntl_lower.

Examples

Consider the controlled limiter in the above image, with the following characteristics:

  • Pin1 (input) is connected to net In
  • Pin2 (cntl_upper) is connected to net Vupper
  • Pin3 (cntl_lower) is connected to net Vlower
  • Pin4 (output) is connected to net Out
  • Designator is U1
  • Gain = 2
  • Limit_Range = 0.1
  • All other model parameters are left at their inherent defaults

The entry in the SPICE netlist would be:

*Schematic Netlist:
AU1 IN VUPPER VLOWER OUT AU1CLIMIT
.MODEL AU1CLIMIT climit (in_offset=0 gain=2 upper_delta=0 lower_delta=0
+ limit_range=0.1 fraction=FALSE)

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 60.00u
  • Transient Step Time - set to 2.000u
  • Transient Max Step Time - set to 2.000u

With the exception of the Initial Value parameter (set to -4V), the Pulsed Value parameter (set to 4V) and the Period parameter (set to 15us), all other parameters for the Pulse Voltage Source have been left at their defaults.

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