| 摘要 |
1,086,187. Automatic frequency control; staircase generating circuits. COMPAGNIE FRANCAISE THOMSON - HOUSTON - HOTCHKISS BRANDT. March 25, 1965 [March 27, 1964], No. 12784/65. Headings H3A and H3P. In a retro-active control system, e.g. an automatic frequency control system, having a search circuit for facilitating initial locking in, the control signal from the search circuit is maintained after locking in to enable a low level of the retro-active control signal to be employed. As described the output from an oscillator 1, Fig. 4, is fed, together with that from a reference oscillator 3, to a frequency comparator 2, the resulting error signal output being fed to control a reactance element 4, e.g. a diode, a valve or a transistor, in the resonant circuit of the oscillator 1. If the frequency of the oscillator 1 lies outside the range of the comparator 2, a staircase generator 6 is switched on to provide a sweep voltage for the reactance 4. When the oscillator 1 comes within the control range, the output from comparator 2 stops the staircase generator, to provide a constant voltage which is then added to that from comparator 2 to control element 4. The staircase generator, Fig. 1 (not shown) comprises a pulse generator 1 feeding a binary divider chain (21, 22 . . . 2n), the output from each stage being half the frequency and twice the amplitude of that from the previous stage. These outputs are then summed in an adding circuit (40), e.g. a resistive network, Fig. 3 (not shown). |
