The BUF602 is a very well controlled part, 1 GHz bw,
low output impedance, closed-loop gain = 1.00. So I expect
the real oscillator to match the sim very well.
On 25/02/2024 4:12 am, John Larkin wrote:
The BUF602 is a very well controlled part, 1 GHz bw,
low output impedance, closed-loop gain = 1.00. So I expect
the real oscillator to match the sim very well.
Perhaps. Neither inductor has any parallel capacitance, and L2 hasn't
got any series resistance either.
Replacing L1 with a 150n Wurth ferrite bead, which does come with full
set of data - the part I picked was 742794 WE-CBF 1806 - stopped it from >working.
A YAGEO company - Pulse sells a 150nH part you can buy from Mouser
PE-0603CD151GTT 150 @ 250MHz 28 @ 150MHz 990 0.92 2
The 990 number is the series resonant frequency of 990MHz which implies
a parallel capacitance of 17pF. The Q was 28 at 150MHz
Plugging that in, and dropping C1 to 25pF did give a working circuit
with a oscillation frequncy of 50.483012MHz.
The second harmonic was 22dB below the fundamental, and the third was
32db down.
A sim is only as good as the component data you plug in.
On Sun, 25 Feb 2024 14:58:13 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 25/02/2024 4:12 am, John Larkin wrote:
The BUF602 is a very well controlled part, 1 GHz bw,
low output impedance, closed-loop gain = 1.00. So I expect
the real oscillator to match the sim very well.
Perhaps. Neither inductor has any parallel capacitance, and L2 hasn't
got any series resistance either.
Stray c will change the frequency slightly, less than component
tolerances.
There's already 40 ohms in series with L2 so a bit more doesn't
matter. About 8 ohms of the 40 is the output impedance of the BUF502.
Replacing L1 with a 150n Wurth ferrite bead, which does come with full
set of data - the part I picked was 742794 WE-CBF 1806 - stopped it from
working.
Sure, oscillators are easy to break if you really want to.
A YAGEO company - Pulse sells a 150nH part you can buy from Mouser
PE-0603CD151GTT 150 @ 250MHz 28 @ 150MHz 990 0.92 2
The 990 number is the series resonant frequency of 990MHz which implies
a parallel capacitance of 17pF. The Q was 28 at 150MHz
Series resonant frequency? 17 pF resonates with 150n at 100 MHz. You
slipped a couple of decimal points. You could use my LC7.exe program.
https://www.dropbox.com/scl/fi/h7l4bkx07fjo78rj83na4/LC7.EXE?rlkey=9cpwpna4begf1u8lfdawibwrl&dl=0
https://www.dropbox.com/scl/fi/yio6yl26ag6wqliafeahc/LC7.txt?rlkey=ncfyzyiav8majni507dgc8qzg&dl=0
I'm using a Coilcraft part, 1812SMS-R15GLB. Q is about 100 at 50 MHz.
SRF 750 MHz, so c=0.3 pF, less than the PCB pads and traces. Tempco is
only 40 PPM.
Plugging that in, and dropping C1 to 25pF did give a working circuit
with a oscillation frequency of 50.483012MHz.
The second harmonic was 22dB below the fundamental, and the third was
32db down.
A sim is only as good as the component data you plug in.
One thing that expedites engineering is knowing which possible effects
don't matter, so can be ignored.
And, I suppose, which people don't matter and can be ignored.
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