74HCU04 LC Osc

Andrew Holme · 2006-10-08T14:16:09+00:00

I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is specified as having a Q of 100: 74HCU04 |\ .------| >O-----o---- | |/ | | .-. | | | | | | 3k3 | 4.8uH '-' | ___ | o------UUU------o | | --- --- --- 390p --- 390p | | | | === === GND GND(created by AACircuit v1.28.6 beta 04/19/05 Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage across either capacitor is about 0.5VThe 3k3 forms a potential divider with the impedance across the capacitor:0.5 / 3 = Z / (3k3 + Z)Z = 660 ohmsDynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z = 2640 ohmsQ = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5Why is my calculated Q so low?TIAAndrew

Oct 08, 2006 41 Replies

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Tony Williams 19 years ago

The thread is still on Google, all 127 posts. "xtal oscillator problems", OP's post 7th March 2002.

Google Groups: sci.electronics.design

Worth a re-read.

Tony Williams.

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Mike Monett 19 years ago

Amazing. Thanks, Tony.

Regards,

Mike Monett

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