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ECE 166 – Microwave Circuits and Systems

Homework #6– Friday December 2, 2011 at 5pm

(High-Gain Amplifier Design, Low-Noise Amplifier Design) 

You will be designing a low-noise amplifier  at 2.5 GHz using the Agilent ATF 34143 amplifier. This is a high

 performance GaAs amplifier with a NFmin of 0.27-0.33 dB at 2.5 GHz (all for 10 cents, amazing!).  All simulationsand plots are to be done in ADS at 0.1-10 GHz. The S-parameters are given on the website.

 Note: ADS can plot many of these parameters for you. See note on the website.

1) Using the S-parameters for 4 V, 60 mA bias (page 10 in the data sheet), calculate and plot:

a)  The unilateral coefficient (U), and the upper and lower bounds of the gain in dB (centered at 0 dB). In

which frequency region is the unilateral approximation valid?

 b)  The Stability Factor, k and . In which frequency region is the transistor unconditionally stable?

c)  The maximum transducer gain in dB (MSG or MAG depending on k) that can be attained using this

device. Compare with S21. This is basically Fig. 26 in the data sheet.

2) Knowing the S-parameters for low noise and high linearity (4 V, 60 mA – and thus the high current for linearity),

and the noise parameters, design an amplifier for low-noise operation at 2.5 GHz for a wireless base station. Clearly

write Gamma(opt), Gamma(s), Gamma(out), Gamma(in) and Gamma(l) at 2.5 GHz, the matching networks used,

and the simulated S-parameters and noise figure (plot from 0.1-10 GHz). Use LC matching. Label the gain, the

output match level (must be good), the input match level (should not be that good), and the noise figure at 0.1 to 10

GHz. Check that the amplifier is stable at all frequencies by plotting the input and output stability circles, and 

Gamma(s) and Gamma(l) (again, ADS does this automatically). Make sure that Gamma(s) and Gamma(l) do not

enter the un-stable regions at their respective frequencies. Make sure that S11 and S22 for the entire amplifier are < 1

(at all frequencies (for stability).

3) Design a high-gain amplifier at 7 GHz using a unilateral approximation, 4 V, 60 mA . Use LC matching circuits

(ideal components). After you have designed the input and output matching circuits to match S11 and S22, connect

them to the transistor and note the real S11 and S22 and gain of the entire amplifier. Since you have made a

unilaterial assumption and the transistor is not really unilaterial, the amplifier S 11 and S22 will not be <-20 dB, but

around -10 dB to -15 dB. Make sure that the amplifier is stable at all frequencies. Plot Gamma(s) and Gamma(l)

and make sure that you are not intersecting any stability circles. All plots should be at 0.1-10 GHz. Simulate the NF

of the high gain amplifier and compare with NFmin that can be attained (if designed as an LNA). Try to get a gain

of 10-11 dB at 7 GHz. 

 If the amplifier is not stable, then you need to reduce the gain a bit (mismatch at certain frequencies, shunt loading

at the output with an LR, series loading with a parallel CR, etc.), and then redo the design.