As you may have seen, the amplifier you simulated in week 5 was using the FLL200IB-2 GaAs High Power MESFET. In the simulation, the transistor was already biased and your task was to apply the circuit matching to tune it to the desired frequency of 680MHz. A datasheet of this transistor is provided for you in the same directory as this assignment specification. You will need to use the data sheet to ascertain some details about the amplifier you have designed. Note, however, that the datasheet does not specify properties for every frequency as is typically the case and so you will need to extrapolate or estimate some values from the data sheet for use at 680MHz. Also note that you do not get any information about the FLL200IB-2 confused with data on the same sheet for the FLL200IB-1 or FLL200IB-3, which you have not used. It is also worth noting some terms or information on the data sheet you may not be familiar with: -

 The pinchoff voltage. This is the gate source voltage where there is minimal or no drain current. Note that such a voltage is negative in this case. - The table entitled “Absolute maximum rating” is the highest possible values of the stated parameters in the table. - The power derating curve. This is a requirement to reduce the voltage and current in the transistor so that there is less power dissipated when the transistor is at a higher temperature than its limit specified in the curve. To exceed it could cause the device to fail substantially. - Measured gain and efficiency values assume that circuit matching has been applied. This is achieved in practice through what is known as load pull measurements. It is recommended for you to have a good read through the data sheet and ensure you understand it. You should present your results of your final tuned circuit from this week’s laboratory. Ensure that you show both your schematic circuit with clear indication of your component values and also your S- Parameters clearly in your results. Ensure you explain clearly the meaning of the S-parameters plotted so that it can be verified why the amplifier is working. (10 Marks) 

Based on the expected maximum output power from the data sheet and the corresponding input power, determine the operational bandwidth of your amplifier setting suitable criteria for the transistor used. Comment also on the consistency of the gain within your chosen bandwidth. (10 Marks) 

In designing your amplifier matching circuits you had to first find the reflection coefficient at the input to your transistor before applying any matching. It is a good idea to check that the value of this reflection coefficient you used in your simulation is in line with what you find from the information on the datasheet. Using the data given in the Smith chart comment on whether the gate and drain of the transistor have a high or low impedance at 680MHz giving reasons for your answer. (10 Marks) 

You will notice from the datasheet that this transistor is designed to operate with a bias suitable for class AB operation. Suppose you were to re-bias the transistor to work for class A operation. Determine the changes you would have to make from what is recommended on the data sheet and would the matching circuit you had designed in this lab be any longer valid? Justify your answer. (10 Marks)

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