RU194055U1 - Low-noise, voltage-controlled oscillator with electronic sub-band switching - Google Patents

Abstract

The proposed device relates to radio engineering and can be used in the construction of generators both to expand the frequency overlap and to reduce the steepness of the tuning characteristic (steepness of the tuning) to reduce the noise level of the generator, for example, when used as part of low-noise wide-range frequency synthesizers. - reduction of noise level at the output of the generator, instability of the generated frequency and the influence of destabilizing factors on leaving the boundaries of the sub-bands of the generator This eliminates the frequency range search system and improves the frequency switching performance. For this, N identical generators are introduced, where N is equal to the number of subbands, and the transistor collectors (VT) of each generator are connected to the corresponding output of the electronic switch (EC1), the input of which is connected to a power source. In this case, in each generator, the emitter of the transistor (VT) is connected to the anode of the switching diode, the cathode of which is connected to the other output of the isolation capacitor and through a resistor that sets the switching current and the switching voltage of the switching diode, with a common bus. 3 ill.

Description

The proposed device relates to radio engineering and can be used in the construction of generators both to expand the frequency overlap and to reduce the steepness of the tuning characteristic (steepness of the tuning) to reduce the noise level of the generator, for example, when used as a part of low-noise wide-range frequency synthesizers.

Foreign frequency synthesizer circuits with built-in generators are known, for example, ADF4350 type manufactured by Analog Devices, MAX2870 manufactured by Maxim Integrated, the disadvantages of which are a decrease in the quality factor and frequency stability of the oscillator circuit (CC) of the generator due to the presence of switching keys in its composition and the possibility of step unevenness changes in capacitance due to the spatial extent of the capacitor matrix, lowering the frequency of the LC generator due to an increase in the total inductance this leads to an increase in the length of the connecting conductors connecting the inductance of the circuit with other elements, which leads to a decrease in the frequency stability of the generator.

The closest analogue in technical essence to the proposed one is a voltage-controlled broadband generator (VCO), described in the article “Design Peculiarities of Broadband Synthesizers Based on a PLL with Integrated VCO” in the journal No. 11/2015 “Components and Technologies” p. 84-87 , a variant of constructing a VCO circuitry is shown in Fig. 2, on page 85, adopted as a prototype.

The prototype generator uses electronic frequency tuning and the formation of subbands by switching capacitors in the oscillator system of the generator and an automatic search system for the optimal subband of the generator, which is necessary due to the very low stability of the generator frequency due to imperfect switching circuits and requiring up to 40 μs for its operation., as follows from the description of the device.

An essential part of the prototype device related to the method of generating the subbands of the generator is shown by the example of two subbands and is shown in FIG. 1, where indicated:

EK1 - electronic switch (EK);

R1 is an isolation resistor;

R2, R3, R4, R5 - resistors that specify the operation mode of the transistor VT1;

R6 is a resistor limiting the control current;

D1 - switching diode;

VD1, VD2 - varicaps;

L1 - inductor of the oscillatory circuit;

C1, C2, C3 - capacitive divider of the oscillatory circuit;

C4 - isolation capacitor;

C5 - switched capacitor of the oscillatory circuit;

VT1 - transistor;

Ey - a source of control voltage;

Ep - source of supply voltage;

Ek is a source of switching voltage.

The prototype device contains an oscillatory circuit of the generator, formed by an inductor L1, a switched capacitor C5, counter-connected varicaps VD1 and VD2 and a capacitive divider C1, C2, C3. The source of the switching voltage Ek through the electronic switch 1 and the resistor R6 is connected to the connection point of the anode of the diode D1 and the output of the switched capacitor C5. The source of control voltage Ey through a resistor R1 is connected to the connection point of the first VD1 and second VD2 varicaps. The anode of the varicap VD1 through the capacitor C1 is connected to the base of the transistor VT1, between the base and the emitter of which the capacitor C2 is connected, and the emitter of the transistor through the parallel connected capacitor C3 and the resistor R5 is connected to the common bus, to which the anode of the second varicap VD2, the cathode of the diode D1 and the other terminal of the inductor L1. The power supply voltage Ep is connected to the collector of transistor VT1 and through a voltage divider from R4 and R2 and resistor R3 to the base of transistor VT1, resistor R2 is connected to a common bus by a different terminal.

The emitter of the transistor VT1 is connected to the capacitor C4, the other output of which is the output of the device.

The prototype device operates as follows.

The first subband (p / d) of the generator is switched on by supplying a switching voltage Ek to the diode D1 through the electronic switch EC1, due to which the capacitor C5 is connected to the oscillator circuit of the generator and, at the lower limit of the control voltage Eu, there is a lower limit on the frequency of the generator for the first p / d. The upper frequency limit of the first p / d is determined by the upper value of the control voltage Eu. Similarly, when a blocking voltage Ek is applied to the diode D1, the capacitor C5 is disconnected from the oscillating circuit and the lower limit of the second subband is determined at the lower limit of the control voltage Eu. The value of the value of the capacitor C5 is selected taking into account the degree of tuning of the varicaps VD1 and VD, and the joining of the boundaries of the subranges and the implementation of continuous overlapping of the generator frequency.

The disadvantage of the prototype device is the decrease in the quality factor and frequency stability of the oscillatory circuit of the generator due to the presence of a switching diode D1 with non-ideal parameters in the open and closed state, which reduces the frequency stability of the generator and increases the noise level of the generator. Further extension of the subbands in this way aggravates this drawback.

The minimum width of the selected VCO subranges is limited by how much of their width is constituted by possible departures of their boundaries due to destabilizing factors (temperature, technological spread, aging, etc.) and the larger their width, the less relevant the possible departures of the subband boundaries.

The task to which the proposed device is aimed is to reduce the noise level at the generator output, to reduce the instability of the generated frequency and to reduce the influence of destabilizing factors on the leaving of the boundaries of the sub-bands of the generator, which eliminates the frequency range search system and improves the frequency switching performance.

To solve the problem, in a low-noise, voltage-controlled generator with electronic switching of subbands, containing an electronic switch, a generator controlled by the voltage of one sub-band with an oscillatory circuit consisting of two counter-series-connected varicaps that are connected in parallel with an inductor and a capacitive divider of three capacitors , while the anode of the first varicap through the first capacitor of the divider is connected to the base of the transistor, between the base and emitter of which key of the second capacitor divider to the emitter of a transistor connected in parallel included a third capacitor and a resistor divider defining a mode of operation of the transistor connected to the other ends of the common bus; a resistive divider is connected between the common bus and the collector of the transistor, the connection point of two resistors of the divider through the third is connected to the base of the transistor; the connection point of the varicaps through a separation resistor is connected to the control voltage input; one output of the isolation capacitor is the output of the device, and also a switching diode and resistor, according to a utility model, the output of the electronic switch is connected to the collector of a transistor, the emitter of which is connected to the anode of the switching diode, the cathode of which is connected to the other output of the isolation capacitor and through a resistor that sets the unlocking current and the switching voltage of the switching diode, with a common bus, in addition, the input of the electronic switch is connected to a power supply source.

A block diagram of the proposed device is shown in FIG. 2, where indicated:

1, 2, N - voltage-controlled oscillators (VCOs) of the respective subbands;

EK1 - electronic switch;

C4 - isolation capacitor;

R6 is a resistor that sets the unlocking current and the switching voltage of the switching diodes;

Ey - a source of control voltage;

Ep is a source of supply voltage.

The proposed device uses N independent, identical generators on N subbands with switching over the supply voltage and switching their outputs with diodes, thereby eliminating the switching of elements directly in the oscillatory circuits of the generators.

The proposed device contains a source of control voltage Eu connected to the inputs of the control voltage N of parallel connected generators. The outputs 1 - N of the VCO are connected through an isolation capacitor C4 to the output of the device and to a resistor that sets the switching current and the switching voltage of the switching diodes R6 - to the common bus. The power supply source Ep is connected to the input of the electronic switch, the N outputs of which are connected to the power supply inputs of each of the N generators, respectively.

A circuit of a generator controlled by the voltage of one of the subbands is shown in FIG. 3, where indicated:

R1 is an isolation resistor;

R2, R3, R4, R5 - resistors that specify the operation mode of the transistor VT1;

VD1, VD2 - the first and second varicaps;

D1 - switching diode;

L1 - inductor of the oscillatory circuit;

C1, C2, C3 - capacitors of the capacitive divider of the oscillatory circuit;

C4 - isolation capacitor;

VT1 is a transistor.

The generator controlled by the voltage of one subband consists of counter-series-connected varicaps VD1 and VD2, which are connected in parallel with the inductor L1, a capacitive divider from capacitors C1, C2, C3 and form an oscillatory circuit of the generator. The anode of the varicap VD1 is connected through the capacitor C1 to the base of the transistor VT1, between the base and the emitter of which the capacitor C2 is connected, the emitter of the transistor VT1 is connected to the capacitor C3 and the resistor R5 connected in parallel, with other terminals connected to a common bus. An anode of the diode D1 is connected to the emitter of transistor VT1, the cathode of which is connected to an isolation capacitor C4 (Fig. 2). The output of the electronic switch is connected to the collector of transistor VT1 and through a resistive divider, consisting of R4, R2, and resistor R3 - with the base of transistor VT1, while the other output of resistor R2 is connected to a common bus.

In addition, the connection point of the varicaps VD1 and VD2 through the isolation resistor R1 is connected to the input of the control voltage of the generator, and the other terminals of the inductance L1 and the varicap VD2 are connected to a common bus.

The proposed device operates as follows.

Using EK1, the first generator, designed to block the first p / d, is switched on by the supply voltage Ep, while the voltage from the emitter of the transistor VT1 opens the switching diode D1 and, due to the voltage across the resistor R6, the second switching diode of the second p / d generator is closed (in Fig. 3 shown). Similarly, using the electronic switch EK1, the supply voltage Ep is supplied to the collector of the transistor of the N-th VCO, the corresponding diode is opened and the generator of the N-th p / d is turned on

Thus, the proposed technical solution in comparison with the prototype allows you to use it, for example, as part of a low-noise wide-range high-speed frequency synthesizer to significantly increase the speed of the synthesizer by eliminating the need to have a subband search system and get a significant reduction in noise level and improving its basic parameters in due to the possibility of optimizing the parameters of each of the individual generators.

In the proposed device can be used as active elements VT1.1, VT1.2, for example, transistors of type 2T368A9, as varicaps VD1.1, VD1.2, VD2.1, VD2.2 - varicaps of type 2B124A9, as commuting diodes D1.1, D1.2 - diodes type 2D409A9.

When performing the generator according to the scheme of the proposed device, i.e. in the form of a set of separate independent generators switched over the supply voltage to their parts of the frequency range, without switching elements in their oscillating systems, the noise level of the generators can be reduced to 20 dB compared to the prototype, and high frequency stability eliminates the need for a complex automatic search system sub-range, replacing it with a fast-acting system to turn on the desired sub-range according to the generator frequency table by applying a supply voltage to it, which reduces the time included the desired subrange of the generator compared with the prototype tens of times.

Claims (1)

Low-noise, voltage-controlled oscillator with electronic sub-band switching, containing an electronic switchboard connected in series and a voltage-controlled one subband oscillator (VCO), consisting of two counter-series varicaps that are connected in parallel with an inductor and a capacitive divider of three capacitors , while the anode of the first varicap through the first capacitor of the divider is connected to the base of the transistor, between the base and emitter of which key of the second capacitor divider to the emitter of a transistor connected in parallel included a third capacitor and a resistor divider defining a mode other ends of the transistor connected to the common bus; a resistive divider is connected between the common bus and the collector of the transistor, the connection point of two resistors of the divider through the third is connected to the base of the transistor; the connection point of the varicaps through a separation resistor is connected to the control voltage input; one output of the isolation capacitor is the output of the device, as well as a switching diode and resistor, characterized in that (N-1) identical generators are introduced, controlled by the voltage of one subband with an oscillatory circuit, and (N-1) outputs of the electronic switch are connected to the inputs of the corresponding VCO whose control voltage inputs are combined; the outputs of the N VCO are combined and connected to the connection point of the isolation resistor and the isolation capacitor, while in each of the N VCO the output of the electronic switch is connected to the collector of the transistor, the emitter of which is connected to the anode of the switching diode, the cathode of which is connected to the other output of the isolation capacitor and through the resistor, the setting unlocking current and the switching voltage of the switching diode, with a common bus, in addition, the input of the electronic switch is connected to a power supply source.

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