Methods of designing and cascading unneutralized tuned-transistor amplifiers

Single-stage amplifiers using available transistors have been designed for high stability and found to have adequate gain and very low tuning interaction. Further consideration of these results shows that some very simple conditions are satisfied at resonance when the single stage is driven and terminated to produce the maximum gain for a given stability. In order that the previous results be of general use, some effective method of cascading must be developed. This problem can be greatly simplified by requiring that all stages have the same stability at resonance, realizing that the stability off resonance may not be the same as the resonant value. Three methods of cascading have been developed on this basis. One method uses dissipative coupling and appears to be the most practical method of cascading. This method is developed by requiring that each stage of the cascaded amplifier be driven and terminated at resonance under the same conditions for which a single stage would obtain the maximum power gain for a given stability. The actual intermediate-stage gain is compared with the maximum single-stage gain. For practical designs, this difference is less than 6 db. The difference per stage is even less than this calculated value when one considers that for n stages, only (n-l) dissipative interstage coupling networks are required. Thus, for a practical two-stage amplifier design, the gain per stage is less than 3 db lower than the maximum single stage transducer gain.