Hello fellow Qspice users I am Jay, I am new to Qspice and this Forum and I am looking for some help. I found the ¥-Device Externally Set Oscillator which I would like to use but I don’t see an equation that relates the how RT ( Timing resistor value at FREQ) adjusts FREQ. I tried a few RT values but was never able to get it to run at the base frequency set by FREQ. For reference If I set FREQ=8k and apply a 1ohm resistor to Rt, the oscillator runs at 200kHz. Any advice on this would be great. Thanks -J
I have a feeling that Default RT is 100K instead of 1.
In this setup if I assign FREQ=80K, I can get ~80kHz from V(Q) with R1=100kohm.
If I uncomment attribute RT=100K for ¥1, I can get exact same curve.
Hello KS, thanks for the help. Yes, it appears that 100k ohms does the trick. I’m not sure I understand the semantics of the statement “RT Timing resistor value at FREQ Ω 1.” in the Qspice help guide. I read that as 1.0 ohm is the default (so I thought I could vary the base freq between 0 and 100%, by setting Rt between 0 and 1) but I’m just some noob here so what do I know : )
Thanks again. -J
@jay314159265 I did try to study how EXTOSC work in September last year but failed about that until your post came up. I am not totally certain but the default value 1 of RT in Qspice Help may be a typo. By testing EXTOSC, default RT seems to be 100kohms. The hardest part of several ¥-Device is its Symbol, Pin Description and Instance Parameters description in HELP may be a bit confusing. My guess is that when Mike created those devices, thing got change but not updated in help or its symbol. But we can always reverse engineering thing out, which is a way we learn.
By revisit this device, finally get more idea how it works. There are multiple symbol for EXTOSC in Symbol library, here I created examples that use ExtOsc4 and ExtOsc2.
Basically EXTOSC is a VCO, with symbol ExtOsc2, you can control output frequency with voltage through Vres1 and Vres2. In demo circuit, there is a PLL.qsch work in this way, I just try to simplify thing and to identify its Frequency and Voltage formula. Hope it give you more idea how to use this device in Qspice. Feel free to share if you figure anything new or anything wrong in this study.
Wow thanks KS, I wonder why the EXTOSC got included without the correct documentation? Having an “ideal” VCO is a nice feature for SPICE. Now that I have a better idea of what is going on I will continue to use it and post back any updated findings.