What components are inside the input module of the MC12079 IC for UHF division?

AI Thread Summary
The MC12079 IC is being used as a UHF divider by 256, but it is experiencing oscillation at around 10 MHz, even with no signal input. A 47 k resistor was added between the non-inverting input and ground to mitigate this issue, raising concerns about potential impacts on sensitivity and other parameters. Participants in the discussion suggest that the oscillation could be due to layout issues and emphasize the importance of adhering to the recommended resistor values from the datasheet. There is a request for detailed schematics of the input module to better understand its components. Overall, the conversation highlights the need for careful troubleshooting and adherence to design specifications when working with the MC12079.
Ravaner
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Hello. I use a MC12079 as UHF divider by 256. Unfortunately this IC was oscillating at about 10 MHz. To correct this problem I insert a 47 k resistor between non inverting input and Gnd as Inverting input is used for signal to divide. It works, but I would like to know if this can have unwanted consequence on other parameters for example sensitivity. My question : has someone a precise idea of what is inside the input module ( in+ & in-) just in front of 1st flip-flop ( detail schematics) ?
 
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You put the resistor in parallel with the capacitor?

Can you post schematic?
What is the input freq and amplitude?

What do you mean "oscillating at 10MHz"? Is the output 10MHz superimposed on the intended RF, or is it just outputting 10MHz?
Is the 10MHz oscillation full power or at a small parasitic level.

Sounds to me like you may have a layout issue, I would not feel comfortable applying the 47K fix not knowing the root cause of the problem.
 
Hi. Oscillation occurs even with unconnected signal imput. I made several tentatives to join schematics pic but unsuccessfully ! Sorry
 
Ravaner said:
Hello. I use a MC12079 as UHF divider by 256. Unfortunately this IC was oscillating at about 10 MHz. To correct this problem I insert a 47 k resistor between non inverting input and Gnd as Inverting input is used for signal to divide. It works, but I would like to know if this can have unwanted consequence on other parameters for example sensitivity. My question : has someone a precise idea of what is inside the input module ( in+ & in-) just in front of 1st flip-flop ( detail schematics) ?
Seems to have an op amp input. The data sheet shows a 1.2k resistor load between output and ground. The non inverting input has a 50 ohm load resistor. Wondering if you have these in place, obviously with very short connections?
 

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