ltspicepulsevoltage-source
I am trying to create a pulse voltage source in ltspice. The pulse should look like a half cycle of a sine wave however the rise and fall times should be different. I can create such pulse with the PULSE function of ltspice and can create a half cycle sine wave but I don't know how to create a nonsymmetric sine pulse. The rise time should be 10 microseconds and fall time should be 15 microseconds. I added a picture that I drew for you to visualize.
Thanks in advance.
Here is the real behavior of almost the same circuit, installed in a real device.
The differences are that the driving source impedance is unknown (V1 is ideal in the simulation), and the load impedance corresponding to R3 in the diagram is unknown.
The behavior is nowhere near the rosy picture painted by the simulation. (On the other hand it is good enough that the everything works in the DUT).
The horizontal divisions on the graticule represent 500 nS intervals. The upper trace is the transistor's collector: one division is 5V. The bottom trace is from the base: one division is 2V. As can be seen, the rise time is quite slow, taking over 500 nS to rise to more than 90%. What might be considered a solid high logic level is probably not established for some 250 to 300 nS.
Your model seems to consist of 2 voltage-controlled voltage sources. The e in e0 and e1 gives that away (in a spice netlist, e is a vcvs) I'm guessing that the max=0.3 min=-0.3 set the minimum and maximum output voltage.
Now let's see if there is a way to do the same but in a syntax that LTspice understands. Find a manual here it is, the interesting bit starts at page 113:
E. Voltage Dependent Voltage Source
yes that is what we need, now check if it will accept options to limit the minimum and maximum voltage. Hmm unfortunately there's nu such option. Bummer, this also explains why your model does not work !
Now there is also a BV (Arbitrary behavioral voltage source) source, see page 101. There are also some examples here. I think it is possible to replicate the model using the BV.
Best Answer
This is not a very beautiful approach, but it works (for this signal).
First I created two voltage sources, which provide the two halves of the signal.
So V1 is
SINE(0 8 25k 0 0 0 0.25), a 25 kHz sine but only for a quarter cycle, so that it stops at the maximum value.V2 is
SINE(0 8 16k6667 10u 0 90 0.25), 16.67 kHz sine but shifted by 90° so it starts at the maximum, again for a quarter cycle, so that it will stop at zero.The real output is then a BV-source with
V=min(V(Vout1),V(Vout2))so it outputs always the smaller of the two voltages, which works in this case because one starts at the maximum value and the other one stops at the maximum value.The frequencies are easy to calculate: it's just \$f = \frac{1}{4 \times t}\$ where t is either the rise or the fall time.