| 摘要 |
The present invention relates generally to communications, and more specifically to a method and apparatus for minimizing DC offset and second-order modulation products (IM2 noise) while demodulating RF signals. The principle of the invention can be applied to differential, down-conversion circuits ( 50 ) consisting of two differential mixers ( 54, 56 ) in series, a follows: a pair of current sources Ia and Ib are used to provide current to positive and negative channels of the first differential mixer ( 54 ). Providing current to the amplifying transistors of the first mixer ( 54 ) reduces the current drawn through the active mixer switches, reducing the noise generated. The current sources 1 a and 1 b are trimmed in a complementary manner where 1 a=I+Delta 1 , and 1 b=Delta 1 . The value of Delta 1 can be determined in a number of manners; for example, it could be established by testing after the circuit has been fabricated, and the value stored on-chip, for future use.
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