lab2 - ECE 488: RF Circuits and Systems LAB 2: Unbalanced...

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ECE 488: RF Circuits and Systems Spring 2009 LAB 2: Unbalanced Switching Mixers and Bandpass Filters Reference: Lectures 6–8; Chapters 3–5 Due: At end of your lab period. Your Name: Your Net ID: Partner(s): Bench Number: Lab Date: Scores # 3-10/80 # 11/20 Total Lab TA: Circle Lab Section: Mon, Mon-Eve, Wed Introduction In this lab you will build and test an unbalanced switching mixer. The basic concept of the mixer is shown below in Figure 1 and produces an output sig- nal at the di±erence frequency between the LO and RF signals. The mixing is done by the shunt switch, which is opened and closed by the local oscillator. The action of the switch e±ectively produces a mul- tiplication of the RF signal by alternating ones and zeros (switch open and switch closed, respectively) which “chops up” the RF signal. Refer to the de- scription in Homework 3. Answers needed: Make sure you have transferred the sketch from Problem 1c of Homework 3 to Fig- ure 3 of this description and made the appropriate entries into item 2 and Table 1 of this lab description from Problem 2 of Homework 3 before going to lab. You will answer the remaining lab questions (items 3 through 11) during your lab. Lab reports: Your report is due at the end of your lab and should include this lab description with all Figure 1: Diagram for the switching mixer. of the question boxes ²lled in, and perhaps extra 8-1/2 ′′ x11 ′′ sheets for calculations supporting your answers in the boxes, for long answers that need more room, and for any special sketches required, if needed. Number the sections of these notes to cor- respond with the numerical sequence given here. Before Your Lab The actual circuit to be built in the lab is shown in Figure 2. Note that the LO frequency (1.70 MHz) is above the RF frequency (1.1 MHz), a high-side LO. (Remember, it can be either above or below.) The circuit uses an NPN transistor ( Q1 ) as the shunt switch. Since the NPN transistor can only short pos- itive voltages to ground, a positive DC bias is added to the RF input signal so that the voltage applied to the switch is always positive. (An easy way to pro-
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lab2 - ECE 488: RF Circuits and Systems LAB 2: Unbalanced...

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