| 摘要 |
An r.f. mixer suitable for use in an FSK (frequency shift keyed) receiver includes first and second mixer circuits 10, 11 receiving an r.f. signal and respective local oscillator signals which are in phase quadrature relationship. Third and fourth mixer circuits 15, 16 similarly receive the r.f. signal and also respective local oscillator signals which are in antiphase to those received by the first and second mixer circuits 10, 11. A local oscillator 20 provides the in-phase and phase quadrature signals, as well as antiphase versions thereof. Outputs of the first and third mixer circuits 10, 15 are combined in antiphase relationship, as are outputs of the second and fourth mixer circuits 11, 16, these combined outputs O/P1, O/P2 providing output signals with rejection of unwanted signal components, both of an A.M. nature and also quasi-synchronous signals which may arise in the presence of a lower level required binary FSK NRZ signal in a direct conversion receiver. <IMAGE>
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