Cascode amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers
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The cascode amplifier shown in the figure is highly stable over a wide temperature range. The cascade on transistors V2, V3 forms the most common cascode circuit - "common emitter - common base", providing a low input capacitance. The low output impedance of the entire amplifier is achieved by turning on an emitter follower on transistor V4 at its output.
Conventional operating mode stabilization circuits are not applicable for cascode inclusions, since, due to the high intrinsic gain, it is impossible to use deep negative feedbacks without the danger of disturbing the stable operation of the amplifier. The required cascade bias on transistors V2 and V3 is set by a voltage divider formed by the elements V1, R1 - R4. Since the divider current is the collector current of transistor V1, any change in the temperature regime of the amplifier leads to a corresponding change in the base bias of transistors V2 and V3. It should be noted that for effective stabilization, transistor V1 must be of the same type as the others. Even better, if all four transistors are part of a transistor assembly made in a single silicon crystal.
The gain of the amplifier is equal to the ratio of the resistances of the resistors R6 and R7 and is about 10 at a maximum output voltage amplitude of 3 V and a bandwidth of 6 MHz.
Note. In a cascode amplifier, transistor assemblies 1MM6.0, KT365CA, K1HT291, K1NT591 can be used.
Literature
- "Radio, fernsehen, elekfronik" (GDR). 1978, No. 9
Publication: N. Bolshakov, rf.atnn.ru
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