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

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Discussion Overview

The discussion revolves around the internal components of the input module of the MC12079 integrated circuit (IC) used as a UHF divider by 256. Participants are exploring issues related to oscillation at 10 MHz and the implications of adding a resistor to the circuit, as well as seeking detailed information about the IC's internal schematics.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes using a 47 k resistor between the non-inverting input and ground to address oscillation issues, questioning the potential impact on sensitivity and other parameters.
  • Another participant asks for clarification on the configuration of the resistor and capacitor, as well as details about the input frequency and amplitude, indicating a need for more information to diagnose the problem.
  • There is a mention of oscillation occurring even with the signal input unconnected, suggesting a possible layout issue rather than a simple fix.
  • A later reply speculates that the input module may contain an operational amplifier and references the data sheet, noting specific resistor values that should be in place for proper operation.

Areas of Agreement / Disagreement

Participants express differing views on the root cause of the oscillation and the appropriateness of the resistor fix. There is no consensus on the internal structure of the input module or the implications of the modifications made.

Contextual Notes

Participants have not provided detailed schematics, and there are unresolved questions regarding the exact nature of the oscillation and the circuit layout. The discussion lacks definitive conclusions about the internal components of the MC12079.

Who May Find This Useful

This discussion may be of interest to electronics engineers, hobbyists working with RF circuits, and individuals troubleshooting similar issues with the MC12079 IC.

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?