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ECE 166 Microwave Circuits

Homework #6 Tuesday November 29, 2006

(Amplifier and Low-Noise Amplifier Design)

You will be designing a set of amplifiers at 2.5 to 3.6 GHz using the Agilent Silicon AT-41486 amplifier. All

simulations and plots are to be done in ADS at 0.1-6 GHz. The S-parameters are attached in pdf.

High-Gain Amplifier Design at 2.5 GHz:

1) Using the S-parameters for high-gain (8V, 25 mA bias), calculate and plot:

a) The unilateral coefficient (U), and the upper and lower bounds of the gain in dB (centered at 0 dB). Inwhich 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 (MSG or MAG depending on k) that can be attained using this device.

2) Assuming a unilateral transistor, design the input and output matching networks at 2.5 GHz using ideal LC

circuits, and simulate the S-parameters on the same chart (30 dB to +20 dB). Clearly show the matching networks

used. What is the input S11 and S22? They should not be well matched.

3) Design a high-gain amplifier using the bilateral conjugate match, and clearly write Gamma(in) and Gamma(out)

at 2.5 GHz and the matching networks used using ideal LC circuits. Simulate the amplifier S-parameters. Compare

the gain with the unilateral design above.

4) In (3) above, check that the amplifier is stable at all frequencies by plotting the input and output stability circles,

and Gamma(s) and Gamma(l). Make sure that Gamma(s) and Gamma(l) do not enter the un-stable regions at their

respective frequencies. Remember that k is < 1 for f3.1 GHz, so there is a huge frequency regionof instability.

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, etc.) and re-do the design.

Low Noise Amplifier Design at 3.6 GHz:

Knowing the S-parameters for low noise (8V, 10 mA bias), and the noise parameters, design an amplifier for low-

noise operation at 3.6 GHz. Clearly write Gamma(s), Gamma(out), Gamma(in) and Gamma(l) at 3.6 GHz, the

matching networks used, and the simulated S-parameters and noise figure (plot from 0.1-6 GHz). Use LC matching

(ideal components).

Label the gain, the output match level (must be good), the input match level (should not be that good), and the noise

figure at 3.0 to4.2 GHz.

Make sure to check that the amplifier is stable over the entire frequency range, and if it is not stable, then you needto add some mismatch or loss at the output port.

High-Gain Amplifier Design at 200 MHz:

The amplifier is not stable at 200 MHz. Design a high gain amplifier using LC matching networks and see how

much you can push it to get a high gain and always check for stability at all frequencies. Make sure that it is

decently matched (since you do not have a closed form solution, it is going to be hard to match it perfectly well, but

try). Use the S-parameters for high-gain (8V, 25 mA bias).