SU1392613A1 - Frequency syntesizer - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to increase the spectral purity of the output signal by reducing the noise of the fractionality. The usb-sat contains the accumulations of the adder (NS) 1, the digital-to-analog converter (DAC) 2, the low-pass filter 3. A converter (П) 4 of the sequence of sawtooth pulses into a sequence of short short pulses is introduced. After that, the pulses cffl (t) with the reference frequency fd are fed to the clock input HC 1, which has a capacitance b. The content of a (t) NS 1 increases with each clock cycle by the value a given on the other code input NA 1. When HC 1 overflows, the variable number a (t) decreases by the value of b and its further primes | starting with the rest. Formed by t.obr. step function a (t) is converted by the D / A converter 2 to the analogue equivalent A (t) containing an RF period. The sawtooth component is G (t) with frequency e, eliminated by filter 3, and neggerzyudich. the saw-tooth component Gg (t) with frequency fв fd- (a / b) passing through (ильtertr 3 on P4. Gg (t) has the same meaning that its values taken over time interval T in / fc are equal to others. Due to this, the pulses g (t) received at the output of P 4 are periodical, a sequence of pulses with a frequency fg. Consequently, the fractional interference will be significantly weakened. e (L CO ND O5 CO

Description

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The invention relates to radio engineering and can be used in transceiver and measuring equipment.

The circuit of the invention is to increase the spectral frequency of the output signal by reducing the noise of the granularity.

Figure 1 shows an electrical structural diagram of a frequency synthesizer; figure 2 - diagrams of work.

The frequency synthesizer contains an accumulator adder (NS) 1, a digital-to-analog converter (DAC) 2, a low-pass filter 3, and a converter for a sequence of sawtooth pulses into a sequence of rectangular short pulses.

The frequency synthesizer works as follows.

The pulse sequence ((t) with the reference frequency f (Fig. Ia) arrives at the clock input HC 1, which has a capacitance b given by a digital code on one of the code inputs. The content of a (t) NS 1 increases with each clock cycle by the amount a given on the other code input NA 1. When HC 1 overflows, the variable number a (t) decreases by the value of b, and its further increments on the next cycle occur, starting with residue, formed during overflow. The step function a (t) thus formed (FIG. 26 is converted by a DAC 2 to an analog equivalent A (t) containing a high frequency Periodic sawtooth component G. (t) with frequency f., Eliminated by filter 3, and a non-periodic sawtooth the component Gj (t) (Fig. 2c) with the average frequency fv fl in / b, passing

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through filter 3 to the input of converter A.

Converter 2 can be constructed in the form of sequentially connected Schmidt trigger and one-oscillator (not shown).

The component Gg (t) has the property that its values, taken over a time interval Td, are equal to each other, so that the pulse tfg (t) (Fig. 2d) obtained at the output of converter 4 is a periodic pulse sequence with frequency fg. Consequently, the interference fractional will be significantly weakened.

The threshold value Gp of the threshold element included in converter 4 can be chosen over a wide range, namely c / a / 2 6 "o (L - - a / 2), where o (A / a is a scale factor when translating digital values in analog.

Formula reclamation

A frequency synthesizer containing series-connected accumulating summatcp, a digital-to-analog converter and a low-pass filter, in this case the first and second code inputs and the clock input of the accumulating adder are respectively the first and second code inputs and the clock input of the frequency synthesizer, characterized in that the spectral purity of the output oscillations by reducing the noise of fractionalities; a converter of a sequence of saw-tooth pulses is introduced into a sequence of rectangular Short impulses whose input is connected to the output of the low-pass filter.

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Claims (1)

Claim A frequency synthesizer comprising a series-connected accumulating adder, a digital-to-analog converter and a low-pass filter, wherein the first and second code inputs and the clock input of the accumulating adder are the first and second code inputs and the clock input of the frequency synthesizer, characterized in that, in order to increase the spectral purity of the output oscillations by reducing the noise of fragmentation, a converter of the sequence of sawtooth pulses into a sequence of rectangular short pulses, the input of which is connected to the output of the low-pass filter. Fae.