Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

undesired Oscillation problem

Status
Not open for further replies.

liletian

Full Member level 6
Joined
Mar 5, 2008
Messages
337
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,298
Activity points
3,790
Hi guys
I had a problem, when I tested my FM receiver chips, there is an undesired signal around 250KHZ at 20 mV, I did not know where it comes from. One of suspection is from amplifer which might oscillator. I attached my anplifier design, can anyone give me some idea how to test in software if this part is easy to oscillator.
Also what will be a possible noise origan in RF chips? I have mixer and oscillator(current starving inverter oscillator) too. Please add as much comments as you can. How to find if the attached file is easy to oscillate or not in software?
Thanks a lot
 

Is the power supplied by a switching power supply?
 

rudane said:
Is the power supplied by a switching power supply?
no, it is not, it is supplied by a DC voltage of 1.2V and 0.6V
 

Does the tail current source shares a same bias voltage with the 40u/120n? What will it be used for?
For the two stage amplifier, maybe you should add frequency compensation circuits to ensure stablity of the whole system.
 

jianjing526 said:
Does the tail current source shares a same bias voltage with the 40u/120n? What will it be used for?
For the two stage amplifier, maybe you should add frequency compensation circuits to ensure stablity of the whole system.
4u/120n and 2.5u/120n share same voltage with 40u/120n, how to dig it out in software stage? What should I do?
Thanks
 

liletian said:
Hi guys
I had a problem, when I tested my FM receiver chips, there is an undesired signal around 250KHZ at 20 mV, I did not know where it comes from. One of suspection is from amplifer which might oscillator. I attached my anplifier design, can anyone give me some idea how to test in software if this part is easy to oscillator.
Also what will be a possible noise origan in RF chips? I have mixer and oscillator(current starving inverter oscillator) too. Please add as much comments as you can. How to find if the attached file is easy to oscillate or not in software?
Thanks a lot

i observe one thing.. how can vbias connect to the gate of two transistor? no DC path to ground for this node.
 

liletian said:
jianjing526 said:
Does the tail current source shares a same bias voltage with the 40u/120n? What will it be used for?
For the two stage amplifier, maybe you should add frequency compensation circuits to ensure stablity of the whole system.
4u/120n and 2.5u/120n share same voltage with 40u/120n, how to dig it out in software stage? What should I do?
Thanks
Well, your amplifier works in a close-loop configuration. Without any frequency conpensation circuitry. How can it be surely stable? You can have a AC analyse and test the loop stability!

Added after 3 minutes:

surianova said:
liletian said:
Hi guys
I had a problem, when I tested my FM receiver chips, there is an undesired signal around 250KHZ at 20 mV, I did not know where it comes from. One of suspection is from amplifer which might oscillator. I attached my anplifier design, can anyone give me some idea how to test in software if this part is easy to oscillator.
Also what will be a possible noise origan in RF chips? I have mixer and oscillator(current starving inverter oscillator) too. Please add as much comments as you can. How to find if the attached file is easy to oscillate or not in software?
Thanks a lot

i observe one thing.. how can vbias connect to the gate of two transistor? no DC path to ground for this node.
I think vbias is provided by other circuitry! It's an input for the amplifier. DC path to ground exits in the other circuitry!
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top