Author Topic: Tips about this circuit ?  (Read 910 times)

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Offline GregoryTopic starter

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Tips about this circuit ?
« on: October 25, 2019, 02:36:53 am »
Hello guys! I designed and tested this 10Mhz amplifier, filter and buffer.

The idea is that a 10Mhz signal from a Rubidium Standard comes in and the crystal filter and buffer output stages will be replicated 6 times for 6 output channels.

I prototyped this circuit and it appears to work really well.

Do you have tips for improvement?





thank you!

Offline bob91343

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Re: Tips about this circuit ?
« Reply #1 on: October 25, 2019, 05:16:05 am »
Input and output impedance and levels?  Pic of waveform?

If you are doing this six times, the input impedance has to be 6 times higher to avoid overloading the source.
 

Offline dom0

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Re: Tips about this circuit ?
« Reply #2 on: October 25, 2019, 11:32:13 am »
The absurdly high Q value of the quartz circuits can pull the average output frequency from the mean value at the input. I think these can be used, but you would have to reduce their Q considerably (dampen the crystals with a resistor of a couple hundred Ohms across them).
,
 

Offline ArthurDent

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Re: Tips about this circuit ?
« Reply #3 on: October 25, 2019, 02:06:40 pm »
You might want to check what has already been done in the past to get ideas. A number of frequency standards used xtal filter/buffers on the output of their oscillators, like this HP schematic shown. The manuals quite often has a section on theory of operation that might be useful.
 

Offline GregoryTopic starter

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Re: Tips about this circuit ?
« Reply #4 on: October 25, 2019, 06:13:31 pm »
Quote
Input and output impedance and levels?  Pic of waveform?

If you are doing this six times, the input impedance has to be 6 times higher to avoid overloading the source.

The output impedancia of the standard is ~50ohm. The output of my circuit is ~50ohm through the 47ohm output resistor.
The follower stage after the comom emitter stage generate the low impedance signal to drive the 6 crystal filters.

The input has 3.5Vpp and the output 2.4Vpp (~11dbm on 50ohm)

Quote
The absurdly high Q value of the quartz circuits can pull the average output frequency from the mean value at the input. I think these can be used, but you would have to reduce their Q considerably (dampen the crystals with a resistor of a couple hundred Ohms across them).

Why?

Quote
You might want to check what has already been done in the past to get ideas. A number of frequency standards used xtal filter/buffers on the output of their oscillators, like this HP schematic shown. The manuals quite often has a section on theory of operation that might be useful.

Thank you!

Here on my instagram I have a picture of the output stage without and with the filter.
https://www.instagram.com/metslab/

The harmonic content of the output has bigger even harmonics, I think because the class A emitter folower of the output stage. Anyway, I think it`s working fine.



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