Ne VFO models for Square Wave Response http://groups.yahoo.com/group/soft_radio/files/SDR%20Spice%20Analysis%20Files/squarewave%20models.zip
Mike, a member of this group made some comments about modeling the VFO with square waves. And so this file is that, and it includes a way to mimic and test the correction making wave forms. To do that, I simply added a transformer to create delays in the digital input signal and now the circuit tries to make corrections to the VFO such as I have seen on the oscilloscope. The transformer is a test device only. Changes for the square wave are as follows. The PRE and CLR pins both want to work on the D input. And so, you can disconnect them from V3 and connect them to D. And add the following to the subscript of V3 PULSE(0 5 0 10n 10n 5u 10u) V3 then will be a square wave generator and the change in the pins seems to work best this way for the digital input signal. I have done this in these files so you do not have to. Problem Report: I have had a report of a problem with the 74HC74 Spice model in the Digital VFO files. The VCC 5 volt line may be off in the Component Attribute Editor window. Just click on the 74HC74 to get the editor window. If you get Spice Model VCC 0 Then click that and in the little window at top, type VCC 5 to set the supply voltage. If it reads VCC 0 there is no supply voltage. And the model does not have a ground depicted, this is however in the subscript or 74HC.lib file. If set right, then the following is seen in the Component Attribute Editor. Spice Model VCC 5 Spice Line VCC=5 SPEED=1.0 TRIPDT=1e-9 The only other reason that the file might not be working for some is that the software has not located the 75hc.lib file in the folder. You can copy and paste a copy into the " sub " folder: link to sub folder: file://C:/Program%20Files/LTC/SwCADIII/lib/sub About that ground again: I think there is a misunderstanding here? Don't worry about a ground pin or setting the ground. You do not have to set any information about the ground. Do not assume that the grounding pin is floating above ground in this model, because if that was true, the chip would not be on and hence not working. And well, the 74HC74 symbol does not depict the ground. If you will look in the DC Operating Point plot you will see that there is a Ix (u1:VGND) device current, which is the mysterious missing ground pin. And it tells you that the ground is part of the unseen subcircuit. And so, you will not find pin VGND no matter how hard you look. So do not try and find the ground. The ground pin is already set at ground and you can not change it unless you rewite the .lib file and make a change in the device symbol. I do not have a problem with the circuit running for me, but if you have a problem check the Component Attribute Editor and set the devices VCC power supply input. You will notice that the Flip Flop symbol does not have either a ground or a +VCC pin. And perhaps add a copy of the .lib file to the sub folder in Switcher CAD III. If you are trying to use this with some other software then I can not help you. You are on you own in that case. In the data sheet of the chip, pin 14 is VCC +5V and pin 7 is ground. In the beginning with this 74hc.lib file I too had to find and turn on the VCC line to get the chip to running in LTspice. And the model should have that set already when you click it on. Since then, every model I designed worked for me very well. Dan
