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Unformatted text preview: EE3220 Homework #1 Solutions February 10, 2006 7.2 Identify the signal and bias components of the output voltage V out and determine the instantaneous signal power extracted from the V S source. What is the signal power transfer ratio of the circuit? + 5 V 1k Ω V S 1k Ω 2sin ω t V R 1 V B R L V out + + The diode is forward biased by the 5 V source and will remain forward biased at the minimum peak v s . We will assume the voltage drop across the diode is 0.7 V and that there is no internal resistance in the diode. Determination of loop current (KVL) 0 = V S V diode V R 1 + V B V out 0 = 2 sin ωt . 7 I (1 kΩ) + 5 I (1 kΩ) I = 2 . 15 + sin ωt mA ∴ V out = 2 . 15 {z} bias + sin ωt  {z } signal V Signal power delivered by source P S = V S I = 2 sin ωt V × sin ωt mA = 2 sin 2 ωt mW Signal power delivered to load P L = I 2 R L = (sin ωt mA) 2 (1 kΩ) = sin 2 ωt mW 1 Signal power transfer ratio P L P S = 2 sin 2 ωt mW sin 2 ωt mW = 1 2 7.5 An amplifier driven by a signal voltage source delivers power to a resistive load, producing power gain. The power drawn from the signal source is minimal. From where does the remaining power delivered to the load come? From the power supply. 7.7 An amplifier produces a sinusoidal signal of 8.5V peak across a 50Ω resistive load. The amplifier is powered from a 12V voltage source. a) What is the signal power delivered to the load? P L avg = V 2 rms R L = V 2 peak 2 R L = 8 . 5 V 2 2(50Ω) = 0 . 72 W b) How much current is drawn from the power supply if the amplifier has an overall efficiency of 25 P amp × 25% = P L P L = . 72 W . 25 = 2 . 9 W I amp = P amp V amp = 2 . 9 W 12 V = 241 mA 7.8 A microphone with an average output voltage of 5mV and a series resistance of 10kΩ acts as the input source to an amplification system that must drive an 8Ω loudspeaker. a) How much power will be delivered to the loudspeaker if the microphone is connected to it directly? Compute the resulting power transfer ratio. Connecting the microphone directly to the loudspeaker puts it in series with the loud speaker load, thus: = V mic I R mic I R loudspeaker = 5 mV I (10 kΩ) I (8 Ω) I = 5 mV 10 kΩ + 8 Ω = . 5 μ A P L = I 2 R = (0 . 5 μ A) 2 (8 Ω) = 2 pW P L P S = P L IV S = 2 pW (0 . 5 μ A)(5 mV) = 8 × 10 4 b) How much power will be delivered to the loudspeaker if the microphone drives an inverting amplifier with an input resistance of 5 kΩ, and output resistance of 2 kΩ, and a gain of 25? The inverter output drives the loudspeaker load. Compute the resulting power transfer ratio....
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This note was uploaded on 04/20/2008 for the course EE 3220 taught by Professor Audiffred during the Spring '06 term at LSU.
 Spring '06
 Audiffred
 Volt

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