1. INVESTIGATION of noise in amplifiers operating in gain compression
Undergraduate Research Presentation (EPSCoR) Spring 2010
Department: Electrical and Computer Engineering
Date: 24th April 2010
Venue: University of Wyoming Classroom Building Rm 115
Prepared by: Chepchumba Soti Limo
Advisor: Dr. Eva Ferre-Pikal

2. HIGHLIGHTS Introduction Background Objectives Simulations
Measurement Systems
Results
Conclusion

3. INTRODUCTION:
Noise: According to Motchenbacker and Connelly, noise is “any unwanted disturbance that obscures a desired signal.
All signal that are transmitted go through some processing after they have been received
All signals become weaker as they are being transmitted therefore necessary to amplify signal after receiving it
Unfortunately, amplifiers add noise to the signal therefore degrading the system performance.

4. Types of Noise Phase Noise: Fluctuations at the zero crossings
Amplitude Noise: Fluctuations at the peaks

5. BACKGROUND
Transmitters and receivers have oscillators
A basic oscillator consists of an amplifier and a filter connected in a closed loop
The amplifier in the oscillator is the main source of noise when the oscillator is operating in very high frequencies
Gain Compression Region
This is the region where the amplifier is no longer linear i.e. the output power is no longer proportional to the input power
Why are we interested in studying amplifiers operating in gain compression?
Most amplifiers in the oscillator operate in gain compression

6. OBJECTIVES
For this project the common emitter (CE) amplifier shown below was built.
The main aim of this project is to see how varying the value of the inductor L1 (20nH and 100nH) will affect the PM noise of the amplifier when operating in gain compression .
All measurements were taken at a frequency of 500MHz.

7. SIMULATIONS
Before proceeding to build the circuit, we had to make sure that the DC bias of the amplifier was just right i.e. that we were not passing to much current through the transistor to destroy it.
Waveform of the magnitude of the gain (Vo/Vi) in the frequency range 10 KHz to 10 GHz

8. Waveform of the phase of the gain (Vo/Vi) in the frequency range 10 KHz to 10 GHz
Apart from making sure our amplifier is biased just right, the simulations help us know how much gain we can expect when we take our measurements. That is what the graphs in this sections represent.

9. MEASUREMENT SYSTEM Dynamic Signal Analyzer SR785
Instruments used:
Agilent E360A Tripple Output Supply
Provided the DC supply needed to power the amplifier
6062A Synthesized RF Signal Generator
Provided the input AC signal at 500MHz
Dynamic Signal Analyzer SR785
Used for injecting the noise into the circuit, measuring the phase noise and measuring the low frequency noise at the collector and the base
Giga-Tronics 8541C Universal Power Meter
Used for measuring the input and output power of the system
LeCroy 9310M Dual 300Mhz Oscilloscope
Used for callibrating the amplifier which helped in calculating the actual phase noise of the circuit

10. Using the information gotten form the measurements taken from the instruments mentioned previously, we were able to measure the total noise in the amplifier, and since we injected a known low frequency noise signal into our amplifier, we were ale to calculate the actual phase noise that the amplifier injects into the overall system.
The low frequency noise that was injected into the system was a sinusoidal signal with an amplitude of 50Vpk and a frequency of 50Hz.

11. RESULTS
We started by characterizing the amplifier so that we can identify where exactly the 1dB, 2bB and 3dB compression points are. This is because this are the three points at which we are going to take readings at and compare.
We started with the 100nH inductor and the characterization graph is shown below.

12. After characterizing the amplifier, we were able to establish the 1dB, 2dB and 3dB points for the 100nH inductor as follows:
1dB => Pin = dB
2dB=> Pin = dB
3dB=> Pin = dB
Once we knew what the exact input power needed for the CE amplifier, the system for measuring the phase noise was set up and calculations done. A summary of the results are listed as follows:
@ 1dB
Phase Noise = dB
@ 2dB
Phase Noise = dB
@ 3dB
Phase Noise = dB

13. CONCLUSION
Because of time and all the obstacles we have had to overcome in building the circuit and taking measurements, we have just been able to successfully complete the first phase of this project.
However, since the circuit is already built and the measurement system is already set up, taking measurements for the second phase of this project should not take nearly as long as the first phase. The most time consuming part will be changing the inductor.
With the results we have obtained so far, they seem to be consistent with the theory behind this project.
Since the main objective is to compare the results we have obtained with the ones we are yet to get, I am unable to do any comparison. It is for this reason that I do not have a conclusion now.

14. THANK YOU