| 摘要 |
A signal handling stage provides variable gain, for example for automatic gain control functions, in a radio frequency tuner. The stage comprises a transconductance stage 1 having negative feedback via further transconductance stage 7. The output current of the transconductance stage 1 is supplied to an AGC core 2, which steers the output current between output loads 3 and 4 and loads for driving the transconductance stage 7 in accordance with an AGC voltage. The amount of negative feedback is therefore varied in accordance with the AGC voltage. For relatively low gain, a large amount of feedback is used and this improves the distortion performance. For relatively high gain, the negative feedback is reduced but a good noise figure can be achieved. <IMAGE>A signal handling stage provides variable gain, for example for automatic gain control functions, in a radio frequency tuner. The stage comprises a transconductance stage 1 having negative feedback via further transconductance stage 7. The output current of the transconductance stage 1 is supplied to an AGC core 2, which steers the output current between output loads 3 and 4 and loads for driving the transconductance stage 7 in accordance with an AGC voltage. The amount of negative feedback is therefore varied in accordance with the AGC voltage. For relatively low gain, a large amount of feedback is used and this improves the distortion performance. For relatively high gain, the negative feedback is reduced but a good noise figure can be achieved. <IMAGE> |
