| 摘要 |
PURPOSE:To eliminate the need for the use of a high voltage for a DC drive voltage source even if the voltage gain variable width is increased by connecting a control terminal of 1st and 2nd attenuation transistors (TRs) to a common DC bias constant voltage source. CONSTITUTION:Gates being control terminals of the 1st and 2nd attenuation TRs Q3, Q4 are connected to a common DC bias constant voltage source 5. Since no signal is inputted to the attenuation TRs Q3, Q4, the voltage gain is decided by a current flowing to amplifier TRs Q1, Q2 and the minimum voltage gain is decreased nearly to zero independently of the current flowing to the attenuation TRs Q3, Q4. Thus, a lower voltage is enough for the voltage of the DC drive voltage source 1 than that of a conventional variable gain type differential amplifier circuit even when the voltage gain variable width is increased.
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