RU2212756C2 - Frequency synthesizer - Google Patents

Abstract

FIELD: radio and communications engineering; frequency synthesizing. SUBSTANCE: frequency synthesizer has phase-locked loop, variable-frequency oscillator, mixer, intermediate-frequency channel, phase-frequency detector, and loop filter, as well as amplitude detector, small frequency spectrum sensor, large frequency spectrum sensor, frequency control unit, reset element, two switches, and current generator. EFFECT: enhanced speed. 1 cl, 1 dwg

Description

 The invention relates to radio and communications technology and can be used in the synthesis of frequencies.

 In the description of the invention [1] a frequency synthesizer is presented, which comprises a tunable generator, a mixer, an intermediate-frequency path with a controlled passband made in the form of a low-pass filter and a switch, a frequency-phase detector, a loop filter, an amplitude detector, a fine-frequency grid sensor, coarse grid sensor, frequency control unit and reset element.

 However, in the known frequency synthesizer, considerable time in the tuning process passes until the moment when the signal in the summing loop of the phase-locked loop is in the passband of the intermediate frequency path. This time takes the greater share in the tuning process, the wider the frequency range of the coarse mesh sensor.

 The objective of the invention is to increase performance.

 To do this, a frequency synthesizer containing a tunable generator, a mixer, an intermediate frequency path with a controlled passband made in the form of a low-pass filter and a first switch, a frequency-phase detector, a loop filter, an amplitude detector, a fine-frequency grid sensor, a large-frequency grid sensor , a frequency control unit and a reset element, a current generator and a second switch are introduced. The output of the current generator is connected to the output of the loop filter through a second switch, the control input of which is connected to the output of the amplitude detector.

 The drawing shows a structural diagram of the proposed device.

 The frequency synthesizer includes a tunable generator 1, a mixer 2, an intermediate frequency path 3, made in the form of a low-pass filter 4 and a first switch 5, a frequency-phase detector 6, a loop filter 7, an amplitude detector 8, a fine frequency grid sensor 9 (LCM), a coarse frequency grid sensor 10 (DCCH), a frequency control unit 11 and a reset element 12, as well as a second switch 13 and a current generator 14, introduced.

 In quasistatic, i.e. synchronous operating mode, a phase-locked loop, including an adjustable oscillator 1, mixer 2, intermediate-frequency path 3 with a controlled passband, made in the form of a low-pass filter 4, the first switch 5 and a frequency-phase detector 6, sums the frequencies of the DMSCH 9 and the DCSCH 10, i.e. the frequency of the signal at the output of the generator 1 is equal to the sum of the frequencies of the sensors 9 and 10 frequencies. In this mode, a signal is present at the input of the amplitude detector 8. The first switch 5 provides a wide (ΔFш) bandwidth of the intermediate frequency path 3 by switching the cutoff frequency of the low-pass filter 4. The value ΔFш according to [1] is chosen to be higher than the upper nominal frequency of the LSSM 9. At the output of the frequency-phase detector 6 and the input of the loop filter 7, there is a voltage corresponding to the phase difference of the input signals, which controls the frequency of the tunable generator 1.

 The loop filter 7 corrects the frequency-phase characteristic of the phase-locked loop, providing a stability condition.

 The signal from the amplitude detector 8, the second switch 13 is turned off, so the current generator 14 is not connected to the output of the loop filter 7.

 Suppose, on a command from the first output of control unit 11, a new frequency is set in the DMCH 9. In this case, the frequency of the signal at the output of the mixer 2, corresponding to the difference in the frequencies of the signals of the tunable generator 1 and the DCCH 10, is within the wide (ΔFш) bandwidth of the path 3. There is a signal at the input of the amplitude detector 8. The voltage from the device 8 controls the first switch 5, which maintains a wide (ΔFш) bandwidth of the intermediate frequency path 3. At the output of the frequency-phase detector 6 there is a signal that changes the voltage at the output of the loop filter 7, trying to reduce the frequency difference at the inputs of the frequency-phase detector 6 to zero, i.e. go to synchronization until the phase difference. As a result, the frequency of the signal at the output of the tunable generator 1 will have a new value equal to the sum of the frequencies of the signals DMSCH 9 and DKSCH 10.

 Suppose, on command from the second output of control unit 11, a new frequency is set to DCSCH 10. At the same moment, the control voltage at the output of loop filter 7 is reset by command from the third output of frequency control unit 11. In this case, the frequency of the signal at the output of the mixer 2, equal to the difference between the frequencies of the signals of the tunable generator 1 and the DCCH 10, is greater than the bandwidth of the intermediate frequency path 3 (ΔFш). At the input of the amplitude detector 8, the signal disappears and the first switch 5 by switching the cutoff frequency of the low-pass filter 4 provides a narrow (ΔFy) bandwidth of the path 3. The ΔFy value is chosen to be significantly lower than the lower nominal frequency of the DMSCH 9, i.e. the condition ΔFу << ΔFш is fulfilled. Simultaneously with the disappearance of the signal at the output of the detector 6, a switch 13 is turned on, which connects the current generator 14 to the output of the loop filter 7. There is a rapid increase in voltage at the output of the loop filter 7.

 The frequency of the tunable generator 1 will begin to increase rapidly. An increase in the frequency will occur until the frequencies from the outputs of the tunable generator 1 and the DCCH 10 differ by an amount not exceeding ΔFy. As soon as this happens, signals will appear at the output of path 3 and amplitude detector 8, and the last signal will switch the bandwidth of path 3 to ΔFш and, through the second switch 13, disconnect the current generator 14 from the output of the loop filter 7. From this moment, the output voltage increases the loop filter 7 will be slower and only due to the signal of the frequency-phase detector 6. Next, the frequency of the tunable generator 1 will be fine tuned to the sum of the frequencies of the DMSCH 9 and the DKSCH 10 up to a phase difference.

 The described mechanism for increasing the rate of increase in voltage at the output of the loop filter 7 until the signal hits the narrow band of the intermediate frequency path 3 can significantly reduce the tuning time of the synthesizer. This gain is greater, the wider the frequency range covered by the DCSCH 10.

Sourse of information
1. Patent 1691960, H 03 L 7/16, Frequency synthesizer. A.I. Belyakov, S.Kh. Kesper.

Claims (1)

 A frequency synthesizer containing a tunable oscillator, mixer, intermediate frequency path, phase-phase detector and loop filter connected to a phase-locked loop, as well as an amplitude detector, the input of which is connected to the output of the intermediate frequency path, a fine frequency grid sensor, the output of which is connected to the second input of the frequency-phase detector, a large frequency sensor, the output of which is connected to the second input of the mixer, as well as a frequency control unit, the first output of which is connected to the input fine mesh sensor, the second output is with the input of the large mesh sensor, and a reset element, the input of which is connected to the third output of the frequency control unit, and the element output is to the output of the loop filter, while the intermediate frequency path consists of a low-pass filter and the first a switch, the input of which is connected to the output of the amplitude detector, and the output to a low-pass filter, characterized in that a second switch and a current generator are introduced into it, and the output of the current generator is connected to the output of the loop filter of the second switch control input coupled to an output of the amplitude detector.