07.Class A amplifiers
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142 CLASS A AMPLIFIERS
R odd1
R odd2
50 Ω
50 Ω
R odd1
FIGURE 7.15 Power combining four transistors [7,8].
PROBLEMS
7.1Using the flow graph reduction method, verify the reflection coefficient found in Eq. (7.17).
7.2The measured scattering parameters of a transistor in an amplifier circuit are found to be the following:
jS11j |
6 |
S11 |
jS21j |
6 |
S21 |
jS12j |
6 |
S12 |
jS22j |
6 |
S22 |
0.85 |
32 |
3.8 |
145 |
0.04 |
74 |
0.92 |
15 |
||||
(a)Determine the stability factor, k, for this transistor.
(b)Determine the y parameters for this circuit.
(c)Determine the circuit that would neutralize (almost unilateralize) the circuit. While this procedure does not guarantee stability in all cases, it always helps lead toward greater stability.
(d)Determine the new scattering parameters for the neutralized circuit.
(e)Determine the generator and load impedances that would give maximum transducer power gain (not unilateral power gain).
(f)What is the value for the maximum transducer power gain.
7.3Determine the transfer function for the flow graph in Fig. 7.16.
7.4A certain transistor has the following S parameters:
S11 D 1.2, S21 D 4.0, S12 D 0, S22 D 0.9
Determine whether this transistor is unconditionally stable.
REFERENCES 143
a |
b |
c |
d |
e
f
FIGURE 7.16 Flow graph for Problem 7.3.
REFERENCES
1.H. L. Krauss, C. W. Bostian, and F. H. Raab, Solid State Radio Engineering, New York: Wiley, 1980, pp. 371–382.
2.P. J. Khan, Private communication, 1971.
3.J. M. Rollett, “Stability and Power-Gain Invariants of Linear Twoports,” IRE Trans. Circuit Theory, Vol. CT-9, pp. 29–32, 1962.
4.D. Woods, “Reappraisal of the Unconditional Stability Criteria for Active 2-Port Networks in Terms of S Parameters,” IEEE Trans. Circuits and Systems, Vol. CAS-23, pp. 73–81, 1976.
5.T. T. Ha, Solid State Microwave Amplifier Design, New York: Wiley, 1981.
6.S. G. Burns and P. R. Bond, Principles of Electronic Circuits, Boston: PWS Publishing, 1997.
7.R. G. Reitag, S. H. Lee, and D. M. Krafcsik, “Stability and Improved Circuit Modeling Considerations for High Power MMIC Amplifiers,” 1988 IEEE Microwave Theory Tech. Symp. Digest, pp. 175–178, 1988.
8.R. G. Freitag “A Unified Analysis of MMIC Power Amplifier Stability,” 1992 IEEE Microwave Theory Tech. Symp. Digest, pp. 297–300, 1992.