基本信息
摘要：858,199. Diode gating circuits. MARCONI'S WIRELESS & TELEGRAPH CO. Ltd. April 9, 1959 [July 17, 1958], No. 23027/58. Class 40(6). Fig. 2 shows a coincidence detector for producing an output on lead 10 only when positive going input signals are present simultaneously at leads 1, 2 and for preventing a noise signal being produced at the output simulating a useful signal even when the two inputs are not simultaneously present. The input signals at 1, 2 are applied to an AND gate comprising semiconductor diodes 4, 5 and also to an OR gate comprising diodes 11, 12 to produce signals at points 3, 13 which are applied to a differential circuit 14 which produces an output to operate relay device 15 when there is a difference in amplitude between the input signals. Since the AND circuit produces an output which is approximately equal to the smaller of its two input signals if large useful signals are present simultaneously at inputs 1, 2 the signals at 3, 13 are of equal amplitude so that no output signal is produced from differential circuit 14 and relay 15 does not operate. If a large signal is present at only one of the inputs 1, 2 the signal at 13 will be very much greater than the signal at 3 so that the differential circuit 14 will actuate relay contact 15 to insert attenuation in the output signal path 10. The delay device 18 and the pulse widening circuit 19 compensate for delay in circuit 14 and thus prevent any noise signal getting to the output 10 even for a short period of time. In the modification shown in Fig. 3 the differential circuit 14 is constituted by a long-tailed pair comprising triodes 14a, 14b the output from which controls electronic switch comprises semi-conductor diodes 15a, 15b which are normally biased by resistor 22 and diode 23. The switch is in the input lead to cathode follower 8 from which the output lead 10 is fed. Resistors 20, 21 attenuate signals supplied via 13 to the valve 14a to ensure that with signal and noise simultaneously at terminals 1, 2 the noise levels at the grids of tubes 14a, 14b are substantially the same and the signal at the grid of valve tube 14b is little more than at the grid of 14a attentuation is thus not inserted in the path of output lead 10. If there is no signal at one of the input terminals I or 2 the output from the long-tailed pair 14a, 14b causes attenuation to be inserted.
摘要附图：
