| 摘要 |
A radio receiver having a double-balanced mixer stage comprising two pairs of emitter coupled transistors (T1 to T4), the common emitters of each pair of transistors being connected to identical current sources (T5, T6 and T9). A local oscillator signal is applied differentially to junctions (58, 60) of the base electrodes of the first and fourth transistors (T1, T4) and the second and third transistors (T2, T3), respectively. The rf input signal is applied to the common emitter junctions (50, 52) via damping resistors (R3, R4) which are also connected to respective current sources. Outputs from the pairs of emitter coupled transistors are coupled to cascode stages (66, 68). Further damping resistors (R1, R2) are connected between the differential local oscillator input (22A, 22B) and the junctions (58, 60) of the base electrodes. The damping resistors are of a low value typically 25 ohms and serve to stabilise the double-balanced mixer circuit and prevent it from going into oscillation. |
