| 摘要 |
A temperature compensated amplifier with variable gain and to a radio device having an amplifier according to it. The gain control and temperature compensation of a differential amplifier ( 210 ) are implemented by a control circuit ( 220 ), which has a balanced and differential output (V<SUB>1</SUB>, V<SUB>2</SUB>). The output voltage of the control circuit, or the control voltage, is arranged to be proportional to difference between two source currents (I<SUB>GT1</SUB>, I<SUB>GT2</SUB>), which difference can be varied on both sides of zero. The output of the control circuit is connected to the bases of the differential pair (Q 1 , Q 2 ) of the variable gain amplifier, whereupon the ratio of the output current (i<SUB>out</SUB>) to the input current (i<SUB>in</SUB>) of the pair becomes dependent on the control voltage. This is arranged to be proportional to the absolute temperature, too. A temperature change then changes the control voltage the more the higher the control voltage is. The temperature coefficient is adjusted so that the effect of the temperature on the current difference of the differential pair of the variable gain amplifier is compensated. Owing to differential type control circuit the current gain with temperature compensation can be varied in the whole range 0 . . . 1.
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