SU886252A1 - Digital frequency synthesizer - Google Patents

Description

The invention relates to radio electronics, in particular, to the formation of oscillations with stable frequencies, and can be used in devices for stabilizing the frequency of radio stations. A digital frequency synthesizer is known, containing a series-connected reference oscillator, a digital frequency-phase detector, a first stable current generator, a low-pass filter, a controlled oscillator, and a variable aiming frequency divider whose output is connected to another input of a digital frequency-phase detector The other output of which is connected via the second stable current generator to the input of the low-pass filter 1. However, in a well-known digital frequency synthesizer, the time is not high enough. the stability of the output waveform. The purpose of the invention is to increase the short-term stability of output oscillations. To achieve this goal, a digital frequency synthesizer containing a series-connected reference oscillator, a digital frequency-phase detector, a first stable current generator, a low-pass filter, a controlled oscillator, and a variable division divider frequency divider whose output is connected to the digital frequency-phase input. the detector, another output of which is connected via the second stable current generator to the input of the low-pass filter, a third stable current generator is introduced, the output of which is connected to o input of low pass filter. The drawing shows a structural electrical circuit of a digital frequency synthesizer. Digital frequency synthesizer contains reference oscillator (OG) 1, digital

frequency-phase detector SChFD; 2, generators 3, 4 and 5, stable current, filter 6, low frequency (LPF), controlled oscillator (UG) 7, frequency divider 8 with variable division factor (DPKD). UG 7 through PDKD 8 is connected to ICFD 2, to the second input of which is connected the exhaust gas 1. The outputs of the CSFD 2 are connected with the control inputs of the generators 3 and 4 of the stable signal; The low-pass filter 6, connected between the connected outputs of the stable current generators 3 and 4 and HS 7, forms a ring of pulsed frequency self-tuning (IFAP).

The synthesizer works as follows,

If the difference in arrival time of the input pulses of the CCPD 2 is greater than the width of the dead zone, i.e. , then, depending on which of the input pulses of the CPCF 2 comes first, control pulses appear at one of the outputs of the CCPD 2, as a result of which a stable current generator 3 or 4 starts to work. Moreover, the signs of the currents of the generators 3 and 4 should be correct. From the stable current generator that is working at the same time, current control pulses E are given on the low-pass filter 6. Under the action of these pulses, the output voltage of the low-pass filter 6 is replaced by adjusting the frequency of the HS 7 so that the synchronism state is established in the IFAPH system, and tyi at the same time tends to zero. As soon as it becomes V, there is no regulation in the system.

The lack of synchronism in the system leads to an increase in tn and when the condition t is fulfilled, the process of automatic frequency tuning starts again. However, the synthesizer output signal in this mode of operation has a significant short-term frequency instability. In order to eliminate the short-term instability of the output signal, the synthesizer due to the operation of the IFACCH system in the deadband mode, it is necessary to eliminate the possibility of operating the system in this mode.

The IFAP system does not work in the indicated mode if the condition

 .:

Introduction to. Scheme additional generator 5 stable gok

allows to achieve the operation mode of the IFAP system, in which the above condition is fulfilled. An additional stable current generator 5 with its current affects the LPF 6 input and introduces into its extraction voltage a component with a linearly varying voltage, which constantly displaces the output, one frequency UG 7 relative to the required frequency of the synchronizer. In order to compensate for the constant bias of the output frequency U.G 7 in synchronization mode, the IFAP system generates a typing pulse of duration V, the magnitude of which is proportional to the current value of the additional generator 5 of the stable current J on110 to show that

“,

thirty

1.1

where 3

 0 - generator current value

3 and 4 stable current; TQ - the period of the pulse

EXT. 1. If the width of the dead zone for a specific implementation of a digital frequency converter has a value and j,

then, choose the current J value. of attitude

- s

.

at the same time .b

Thus, the introduction of an additional stable current generator into the digital frequency synthesizing circuit allows yeipaSttTb the appearance of a short-term instability of the output signal of the TOpia synthesis due to the presence of a dead zone due to the finite time of its elements.

Claims (1)

Invention Formula A digital frequency synthesizer containing a series-connected reference oscillator, a digital frequency-phase generator a detector, a first stable current generator, a low pass filter, a controlled oscillator and a frequency divider with an inverted division factor, the output of which is connected to another input of a digital frequency-phase detector, the other output of which is connected via a second stable current generator to a lower frequency input, characterized by that, with a circuit for increasing the 1-time stability of the output oscillations, a third stable current generator was introduced into it, the output of which is connected to the input of the high-frequency filter. 88625 S 24 Sources of information taken into account during the examination 1. US Patent No. 3714463, cl. ZO7-R.32, 1973 (prototype).