next up previous contents index
Next: Piecewise Linear Up: Tran Functions Previous: Pulse   Contents   Index

Gaussian Pulse

General Form:
gpulse(v1 v2 td pw per td1 td2 ... )
vsfq 0 0 gpulse(0 0 20p 2p 0 40p 60p)
vpulse 1 0 gpulse(0 1 100p 5p 100p)

parameter description default value units
v1 base value 0.0 volts or amps
v2 pulse peak value v1 volts or amps
td delay time 0.0 seconds
pw pulse width see description seconds
per period 0.0 seconds

This generates a gaussian pulse signal, and as a special case, as a voltage source will generate single flux quantum (SFQ) pulses.

Warning: The pulse width is interpreted as the full-width half-maximum in release 4.3.3 and later. In earlier releases, this was taken as the ``variance'' (width where amplitude is 1/e of the peak). Presently, this interpretation can be coerced by giving a negative pulse width, the absolute value will be used as the variance.

The expression used to generate a pulse is
pw > 0 :

value = v1 + (v2 - v1) . exp(- (4 . ln(2) . (time - td )/pw)2)
pw < 0 :
value = v1 + (v2 - v1) . exp(- ((time - td )/ - pw)2)

The td delay value specifies the time of the initial pulse peak. The pw defines the pulse width, as described above. If the per is given a nonzero value larger than twice the pw, a train of pulses will be generated, the first being at td and at time increments of per thereafter. A per explicitly zero can be followed by any number of time values. A pulse will be generated to peak at each of these values, in addition to the td value.

A single flux quantum (SFQ) pulse, as a voltage applied across an inductor, will induce a single flux quantum of

$ \Phi_{0}^{}$ = h/(2e) = 2.06783fWb
where h is Planck's constant, e is the electron charge. With superconductors, the flux that threads superconducting loops is quantized in increments of this value, due to the requirement that the superconducting wave function meet periodic boundary conditions around the loop.

If the pw is not given or given as zero, the source will be configured to produce an SFQ pulse with the given amplitude. Thus, the actual pulse width will be computed internally, with amplitude not zero, as

pw = 2$ \sqrt{{ln(2)}}$$ \Phi_{0}^{}$/(abs(v2 - v1)$ \sqrt{\pi}$)
where $ \Phi_{0}^{}$ is the flux quantum whose value is given above.

Similarly, if the amplitude is set to zero, i.e., v2 = v1, the amplitude will be computed from the pulse width to yield an SFQ pulse. The computed amplitude is

v2 = v1 + 2$ \sqrt{{ln(2)}}$$ \Phi_{0}^{}$/(pw$ \sqrt{\pi}$)

If both amplitude and pulse width are set to zero or not given, the full-width half-maximum SFQ pulse width is taken as the TSTEP transient analysis parameter, and the amplitude is computed as above.

In superconducting electronics, single flux quantum pulses are generated and received by logic circuits. A generator of SFQ pulses is therefor a useful item when working with this technology.


* gaussian pulse

v1 1 0 gpulse(0 0 20p 2p 0 40p)
l1 1 2 10p
b1 2 0 100 jj3 area=.2
r2 2 0 2
.tran .1p 100p uic
.plot tran v(1) v(2) i(l1) ysep

* Nb 4500 A/cm2
.model jj3 jj(rtype=1, cct=1, icon=10m, vg=2.8m, delv=0.08m,
+ icrit=1m, r0=30, rn=1.7, cap=1.31p)

In the example, the generator produces two SFQ pulses. The second pulse causes the Josephson junction to emit a flux quantum, the second one from the source is therefor expelled. The inductor current shows the same value before and after the second pulse, as expected.

next up previous contents index
Next: Piecewise Linear Up: Tran Functions Previous: Pulse   Contents   Index
Stephen R. Whiteley 2018-04-22