| 摘要 |
1308646 Frequency synthesizers SCHLUMBERGER OVERSEAS MESSGERATEBAU UND VERTRIEB GmbH 6 May 1970 [10 May 1969] 21723/70 Heading H3F The invention relates to a frequency synthesizer in which the output frequency, e.g. 0-100 MHz is obtained by the subtractive mixing of a stepwisely selectable frequency, e.g. 480-580 MHz and a fixed frequency, e.g. 480 MHz in a final mixing stage 40, the fixed frequency resulting from the additive mixing in an output mixing stage 21 of a particular multiple, e.g. 440 MHz of a constant auxiliary frequency, e.g. 440 MHz and said auxiliary frequency itself. The auxiliary frequency, before being applied to the input of the output mixing stage 21 is amplitude-modulated, i.e. in mixer 22. The arrangement is characterized in that a differential amplifier 45 is connected in the amplitude regulation loop of the synthesizer output frequency, one input 45a of the differential amplifier 45 being supplied with the rectified and filtered synthesizer output voltage, i.e. over rectifier and filter 42. The other input 45b is supplied with the rectified and filtered amplitude-modulated auxiliary frequency in the same phase, i.e. over rectifier and filter 47; the output of the differential amplifier 45 is connected to the control terminal of a continuously gain-controllable attenuator 43 connected between the output mixing stage 21 and the final mixing stage 40. The two rectifier and filter circuits 42, 47 are preferably substantially identical, and their time-constants may be of the same order of magnitude as the modulation frequency period. The output level is controlled either by means of an adjustable attenuator 46 or by means of a D.C. voltage reference source 48 supplying a controllable bias to input 45b of the differential amplifier. The arrangement is such that modulation signals cancel out in the differential amplifier 45, from the control voltage applied to the attenuator 43. |
