| 摘要 |
PROBLEM TO BE SOLVED: To prevent saturation of an emitter grounded transistor and a base grounded transistor with respect to an internal control voltage of a variable gain circuit to obtain a large amplitude signal outputs. SOLUTION: A bias voltage supply circuit is constituted by transistors Q31, Q32, Q33, etc., to supply a bias voltage corresponding to an internal control voltage Vc of a variable gain circuit to bases of base grounded transistors Q25, Q26. Accordingly, the bias voltage of the respective transistors Q25, Q26 fluctuates in proportion to an output DC voltage of the variable gain circuit, and emitter potentials of the transistors Q25, Q26 in proportion to the output DC voltage of the variable gain circuit are supplied to collectors of emitter grounded transistors Q27, Q28. As a result, even if the internal control voltage Vc of the variable gain circuit changes as the base potentials of the transistors Q25, Q26 change appropriately in accordance with the above change, it becomes possible to output a large amplitude signal without saturating the circuit.
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