# Radio Receiver Design .page160

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Amplifier Design and Application                                                       145

Because the 100-ohm resistor appears to be in parallel with the output, an inductor
should be added in series with the resistor. For 500 ohms inductor impedance, its
value should be L = 5 0 0 / 0 = 79 mHy, for operation at loo0 Hz. Again, this
component value would be much smaller for operation at higher frequencies. Dis-
sipation in the 100-ohm resistor would be only i2R = 0.Ol2x 100 = 10 mW. With
careful layout, this amplifier can provide more than 20 dB of gain up to 2 GHz.

QUESTIONS

1. If an amplifier’s input signal is 0.1 V and its output is 15 V, what are its
voltage and power gain? (Assume that input and output impedances are
matched and are 50 ohms.)
2. If the preceding amplifier’s input impedance is 50 ohms and its output
impedance is 300 ohms (both matched), what are the voltage and power gain?
3. What is the output power in questions 1 and 2?
4. What is the difference between          and IP, for an amplifier?
5 . Given that IP, is specified as + 15 dBm and gain is 2 1 dB, what is IIP, for an
amplifier?
6. If an amplifier’s IIP, is given, how can one estimate          ?
7. Given an amplifier with IP, at + 10 dBm and input signals at -20 dBm, what
level of third-order output should be expected?
8. In a receiver whose preamplifier has a noise figure of 2.5 dB, an attenuator
whose insertion loss is 1.2 dB is to be added. What is the effect on the
amplifier? What is the effect on the receiver?
9. An amplifier with 2 dB noise figure and 18 dB gain is to be used to drive a
mixer with 10 dB noise figure and 6 dB gain. Can this combination work for
a receiver with 100 kHz noise bandwidth and 1.O p,V specified sensitivity?
Assume a 10 dB IF noise figure.
10. What Q would be required for an amplifier to operate with a bandwidth of 50
kHz at 10.7 MHz?
1 1 . What is the effect of adding a variable attenuator ahead of a preamplifier?
After the preamplifier?
12. What are the advantages and disadvantages of employing a limiting IF
amplifier in a receiver?

REFERENCES*

I.   Cahn, C. R., A note on signal-to-noise ratio in bandpass limiters, IEEE Truns. Inform.
Theory, Jan. 1961.

*Also see references for Chapter 6.

http___www.philadelphia.edu.jo_

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