Please answer all questions. Thanks. A mixer is used in a vector network analyser to down-convert th

Please answer all questions. Thanks.

A mixer is used in a vector network analyser to down-convert the input signal to base-band. The input frequencies are 1.5 GHz and 2 GHz. GVin A2Vn where G is (a) Assuming a diode is used for the mixer, with a response V0ut the linear gain and A2 is the second-order gain. Calculate the amplitude and frequency of each output frequency component. (5 marks) (b) Figure B1-1 shows the schematic diagram of a double-balanced mixer. Explain how this mixer works. State three advantages of double-balanced mixers over other mixer types. (5 marks) LO Balancing IF transformer for RF input (Balun) Balancing transformer for RF input (Balun) RF Figure B1-1: Schematic diagram of a double-balanced mixer (c) For the diode mixer in part (a), the filter shown in Figure B1-2 is used to remove unwanted frequencies from the mixer output. Derive expressions for the impedance of the series and shunt lines. Use these to calculate the impedances at low and high frequency and determine at what frequency the output is maximised. What type of filter is this? (9 marks) w L L C C C Figure B1-2: Circuit diagram of a filter (d) Consider an inductor with a stray capacitance, explain what is meant by self-resonant frequency (SRF) and show what happens to the impedance of an inductor above the SRF (4 marks) PLEASE TURN OVER (e) Explain how the mixer in part (a) can produce other frequency components other than those stated (2 marks)

 

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