JPS5910081B2 - voltage controlled oscillation circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage controlled oscillation circuit.

A voltage controlled oscillation circuit is a circuit device that can electrically change the oscillation frequency, and is always used in PLL circuits (phase locked loop circuits).

Examples of circuits that apply PLL in consumer machines include the AFC (automatic frequency control) circuit in the horizontal synchronization circuit of television receivers, the APC (automatic phase control 9 circuit) in the color subcarrier regeneration circuit, and the VTR (video tape) circuit. This includes color reproduction circuits for recorders).

In recent years, these circuit sections are gradually becoming integrated circuits (ICs).

In that case, there is a technical problem of how to integrate the voltage controlled oscillation circuit with good stability.

That is, since both television receivers and VTRs use a stationary comparison signal as a reference, they do not require that much of a pull-in range, and rather stability is more important.

Therefore, various proposals have been made in the past. FIG. 1 shows an example of this, in which a variable phase shift circuit 10 consisting of a differential connection of transistors Q1 and Q2 is connected to a feedback circuit of an amplifier 12 consisting of transistors Q3 and Q4 together with a series resonant circuit 11 consisting of L, , C2. It was established.

This oscillator controls the oscillation frequency by changing the control voltage Vc of the transfer circuit 10.

That is, when the control voltage V(, = O, one end 1 of the resonant circuit 11
3, the voltage phase of the output terminal 14 of the phase shift circuit 10, which is the other terminal, is the same, so the circuit is connected to the L of the resonant circuit 11.
1. Series resonant frequency of C2 f−f o =”/2πJ
However, in the case of V(,>O, a voltage whose phase is advanced with respect to the terminal 13 is generated at the terminal 14, so that the resonant circuit 11 oscillates at a frequency f>fo at which the resonant circuit 11 becomes inductive.

Also, on the contrary, V.

In the case of <0, a voltage whose phase is delayed with respect to the terminal 13 is generated at the terminal 14, so that the resonant circuit 11 oscillates at a frequency f<fo at which it becomes capacitive.

However, this circuit has the following problems.

That is, in this circuit, in order to prevent R3 j Lm ) C2 from becoming a load on the phase shift circuit 10,
2 is designed to be a fraction of R3.

Therefore, since the load on Q1 and Q2 is small, a sufficient open loop gain cannot be obtained unless the current source 1 is increased to increase the mutual conductance of the differential amplifier 12 of Q3 and Q4.

In other words, large current consumption is inevitable in order to obtain sufficient open loop gain.

In order to keep this current consumption low, it is necessary to increase R3.

However, since this circuit uses series resonance, the series resistance component R3 of the circuit is multiplied by Q (where Q is the Q of the circuit determined by the control range (=2πfoL1/Ra).

) is required.

Therefore, if R3 is increased, an inductor with a large inductance of, for example, several tens of mH or more is required.

Inductors with such large inductance are generally expensive, and their own high impedance results in poor stability due to stray capacitance and induction.

In addition, this inductor L1 is generally made variable to compensate for variations in the elements, but making an inductor of several tens of mH or more variable as described above becomes extremely expensive.
It is also difficult to manufacture.

Therefore, since there are limitations in manufacturing large 1' inductors, it is naturally not possible to extend the lower limit of the oscillation frequency of the oscillator by using even larger inductors.

That is, in such a circuit, the lower limit of the oscillation frequency is suppressed.

On the other hand, when the oscillation frequency becomes higher than IMHz, self-resonance (
Parallel resonance due to the inductance of the inductor itself and distributed capacitance) cannot be ignored, and the center frequency f.

The control voltage has an asymmetrical frequency characteristic centered around .

Therefore, for this reason, the upper limit of the oscillation frequency is also limited.

In order to avoid the influence of self-resonance of the inductor, it is possible to lower the impedance of the inductor, but in this case R3 and Rl + R2 become small, and a large current is required to maintain the same open loop gain.

Recently, the degree of integration of linear ICs has improved considerably, but the fact that some circuits consume a large amount of power is a major impediment to the improvement of the degree of integration.

? The practical frequency range of this voltage controlled oscillator circuit varies depending on the control voltage, but it ranges from 10 KHz to several 10 KHz.
It is about 0 KHz.

On the other hand, a circuit as shown in FIG. 2 has also been proposed.

This circuit differs from the circuit shown in FIG. 1 in that ten phase shift circuits shown at 21 and 22 are placed on the input side of the amplifier.

In this case, the input impedance of the amplifier is mainly determined by the phase shift circuit, and there is no restriction that the load resistance R1 must be particularly lower than the input impedance, so open loop gain can be secured even with a smaller current than in the circuit of FIG.

However, since the use of series resonance is the same, the achievable oscillation frequency range is not improved.

Another problem is that the impedance seen from point 23 in the phase shift circuit must be resistive, which requires an inductor in the phase shift circuit.

This is not very desirable from the point of view of cost.

Therefore, this circuit is not particularly superior to the circuit shown in FIG. 1 except for current consumption.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a voltage controlled oscillation circuit that can secure a large open loop gain with a small current and has an improved oscillation frequency region.

That is, the present invention provides two amplifiers whose mutual conductance changes differentially with a DC control voltage, excites a parallel resonant circuit with the sum of the outputs of the two amplifiers, and then excites the voltage of the parallel resonant circuit or divides it. The resulting voltage is divided into two components with different phases by an appropriate phase shift circuit,
The present invention provides a voltage controlled oscillation circuit that achieves the above object by feeding back to the two amplifiers.

Hereinafter, the present invention will be explained in detail with reference to embodiments of the drawings.

FIG. 3 shows an integrated embodiment of the invention.

The area within the broken line 30 in the figure indicates the inside of the IC circuit, and the other areas indicate external circuits.

Transistor Q3. tQ3 constitutes a differential amplifier, the emitters of which are connected in common, and grounded via a current source 31 and a terminal 32 as /Mass current input terminals.

Further, the bases of these transistors Q31 and Q32 are connected to control terminals 33 and 34, respectively.

A DC voltage Vo is applied between the control terminals 3334 for controlling the oscillation frequency of the circuit.

On the other hand, transistors Q33, Q34 and transistor Q3
5 t Q36 are each differential? The transistors Qs1t constitute width amplifiers 35 and 36, their respective emits are connected in common, and each serves as a bias current input terminal.
Connected to the collector of Qa.

The base of transistor Q33 is connected to bias terminal 37.

Similarly, the bases of transistors Q34 and Q35 are connected in common and connected to the bias terminal 37 via a resistor 38.

A bias voltage vB is applied to this bias terminal 37.

The bases of commonly connected transistors Q34 and Q35 are connected to terminal 39, and the base of transistor Q3a is connected to terminal 40.

Furthermore, the collectors of transistors Q33 and Q35 are commonly connected to terminal 41, and the collectors of transistors Q33 and Q35 are connected in common to terminal 41.
The collectors of Q4 and Qaa are commonly connected to a terminal 42.

On the other hand, in the external circuit, the power supply voltage ■ is applied to the terminal 42 from the terminal 43, and the inductor 4 is applied to the terminals 42 and 41.
4 and a parallel resonant circuit 46 having a capacitor 45 are connected.

Further, a DC blocking capacitor 47 is provided between the terminals 41 and 40.
Further, a resistor 48 is connected between the terminals 40 and 39, and a capacitor 49 is connected between the terminals 39 and 32.

Next, in order to explain the operation of the above circuit, an equivalent circuit thereof is shown in FIG.

The resistor 38 is a bias resistor inside the IC, but it is connected in parallel to the capacitor 49 in terms of AC.

As a general design, the absolute value of the parallel impedance of the resistor 38 and capacitor 49 is set to be equal to that of the resistor 48.

Therefore, the voltage island across the resistor 48 and the voltage across the capacitor 49 are the same.

The vectors have the same magnitude and differ only in phase.

The vector of voltage M3 between terminals 41 and 32 in FIG.
and M2, the vectors of each voltage are as shown in FIG.

On the other hand, the current II j I2 is the transistor Q33 t Q
Differential amplifiers 35 and 3 consisting of 34 and Q3, , Q36
11 is the product of the voltage M1 and the mutual conductance of the differential amplifier 36, and 12 is the product of the voltage M1 and the mutual conductance of the differential amplifier 35.

The transconductance of a differential amplifier is proportional to the current of the current source connected to the common emitter electrode.

Therefore, when v(3=o, the mutual conductances of the differential amplifiers 35 and 36 are equal, II-11=II21, and when Vc>0, the mutual conductance of the differential amplifier 35 is thicker<+i1+<1121 becomes.

On the other hand, when Vo<O, the mutual conductance of the differential amplifier 36 is larger, 1111>1121.

A vector diagram of II, I2, and v in these three states is shown in FIG.

As mentioned above, 11 is given as the product of M1 and the mutual conductance of the differential amplifier 36, so the vector direction is M
Equals 1.

Similarly, 12 vector directions are equal to M2.

As is clear from the figure, when VC,=O, M3 and 11+
12 phases are equal.

The circuit therefore oscillates at the parallel resonant frequency.

When VC>O, there is a lagging current, so the circuit is inductive.
The oscillation condition is satisfied at a frequency lower than the parallel resonance frequency.

Also, when c<0, the current advances in the opposite direction, so the circuit is capacitive and oscillates at a frequency higher than the parallel resonance frequency.

Therefore, the control characteristics are as shown in FIG.

The phase difference θ between V1 and V2 shown in the vector diagram of FIG. 5 can be arbitrarily set from 0 to 900 by changing the value of the resistor 38, but the larger the value, the more stable the circuit becomes.

However, if the resistor 38 is made too large, the balance of the circuit will be lost, so a range of 60 to 80 degrees is probably appropriate.

The present invention has the following advantages over conventional oscillation circuits.

First, current consumption is reduced. That is, in the circuit of the present invention, bias resistors 38 and 48 serve as load resistances for transistors Q33 t Q35.

In contrast, in the conventional circuit shown in FIG. 1, a resistor that is a fraction of these bias resistors enters the load as a phase shift circuit, so for the same open-loop gain, the required current of the embodiment of the present invention is a fraction of that of these bias resistors. 1 will suffice.

Second, the inductance of the required inductor can be small.

That is, since the conventional circuits shown in FIGS. 1 and 2 both use series resonance, an inductor is required to obtain an impedance that is Q times the series resistance component of the circuit.

However, according to the present invention, the inductance is such that the impedance is 1/Q times that of the parallel resistance component, so if Q=10, for example, an inductor with an inductance that is about two orders of magnitude smaller can be used.

Therefore, the manufacturing margin for obtaining a large inductance increases, which widens the lower limit of the oscillation frequency and reduces costs.

On the other hand, since self-resonance is not a problem at high frequencies, it is possible to design a device that can obtain even higher oscillation frequencies even with a small current.

That is, in the present invention, as long as the voltage controlled oscillation circuit has a control range of the numerical coefficient of the center frequency, it is possible to realize a frequency from about one order of magnitude lower to one order of magnitude higher than the conventional circuit with the same degree of difficulty.

Another advantage is that the phase shift of the circuit can be up to ±45°.
(In practice, it is about ±40°), which is ±2 of the conventional circuit shown in Figure 1.
It is wider than 2.5 degrees and the Q of the circuit is high, improving stability.

Further, in the circuit of the present invention, the transistor Q33 5
The output capacitance of Q35 is only connected in parallel to the capacitor 45 of the parallel resonant circuit 46 and has no effect, but in the conventional circuit of FIG. 1, it delays the phase and lowers the frequency limit.

Further, in the circuit shown in FIG. 1, the change in open loop gain due to the control voltage decreases unilaterally as the frequency increases, whereas in the present invention there is almost no change.

In the embodiment shown in FIG. 3, a resistor 48 is connected between the terminals 40 and 39, and a capacitor 49 is connected between the terminals 39 and 32, but even if the capacitor 49 is connected in parallel to the resistor 48, good.

However, in that case, the sizes of the resistor 48 and the resistor 38 need to be reversed.

In short, terminals 40, 39 and terminal 39. Impedances having approximately the same size and different phases may be connected between the 32 and 32.

Further, the DC blocking capacitor 47 is connected to the terminal 41, but it may be connected to the inductor 44 or capacitor 45 of the parallel resonant circuit 46 by providing a tap thereon.

FIG. 8 shows another embodiment of the invention.

In the embodiment shown in FIG. 3 above, the mutual conductance is controlled by changing the current source connected to the common emitter of the differential amplifier by the control voltage, but in this embodiment, the differential circuits 81 and 82 are The common emitters (bias current input terminals) of the transistors that make up the differential circuits 83 and 84 are connected to the collectors of the transistors that make up the differential amplifier circuits 83 and 84, and the current generated in the collectors is passed through the differential amplifier circuits 83 and 84.
The control voltage Vo applied to the base of the transistor 84
The apparent mutual conductance is changed by so-called current division.

Since the other external circuit configurations and operations are completely the same, the same reference numerals as in FIG. 3 are used to omit the explanation.

Although the number of elements in this circuit increases, terminal 85,
A feature is that the center bias value of the control voltage Vo applied to the circuit 86 can be made higher than that of the circuit shown in FIG. 3, which may facilitate the construction of the phase comparator.

In addition, in this circuit and the circuit in FIG. 3, the transistor Q33
+ Q35 directly drives the parallel resonant circuit 46, however, the parallel resonant circuit 46 may also be driven by providing a load resistor to the transistors Q33 and Q3H and taking out the output to the terminal 41 via an emitter follower.

A special feature of this is that low impedance output can be taken out without adding pins to the IC.

However, it is not suitable for high frequencies. All of the embodiments described above require three external connection terminals in addition to the power supply voltage and ground terminals when integrated.

This is standard for voltage controlled oscillators, but two terminals are also possible if specifically required.

This is a feature not found in conventional circuits.

An example is shown in FIG. This circuit is different from the one in FIG. 3 in that PN elements 91 and 92 are connected between terminal 42 and the base of transistor Q33 and between terminal 41 and the base of transistor Q36, respectively, and the bases of these transistors are connected to a current source. 100 and 101, the DC blocking capacitor is omitted and the number of IC terminals is reduced by one.

Further, PN elements 91 and 92 level shift the power supply voltage V and apply it to the bases of transistors Q33 to Q36.

That is, it provides a certain level of potential difference between the bases and collectors of the transistors Q3a to Q36 to prevent the bases and collectors from turning on.

Usually, one or two PN elements 91 and 92 provide sufficient open loop gain.

As is clear from the above explanation, the voltage controlled oscillator circuit according to the present invention can secure a large open loop gain with a small current compared to the conventional voltage controlled oscillator circuit, and requires only a small inductance. This can greatly expand the low frequency limit due to limitations and the high frequency limit due to self-resonance.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams of conventional voltage controlled oscillation circuits,
FIG. 3 is a circuit diagram of a voltage controlled oscillation circuit according to an embodiment of the present invention, FIG. 4 is an equivalent circuit diagram for explaining its operation, and FIG.
The figure is a voltage vector diagram of a phase shift circuit formed by connecting two impedance elements, Figure 6 is a vector diagram of signals of each part to explain the state in which the oscillation frequency of the circuit of Figure 3 is controlled, and Figure 7 is a diagram showing the relationship between control voltage and oscillation frequency of the circuit of the present invention, and FIGS. 8 and 9 are circuit diagrams showing other embodiments of the present invention. 35, 36. 81-84... Differential amplifier circuit, 46... Parallel resonant circuit, 48... Resistor, 49... Capacity, 47... Single line Capacity for flow prevention.

Claims (1)

[Scope of Claims] 1. First and second differential amplifiers each having a first and a second input terminal, a first and a second output terminal, and a bias current input terminal; A first input terminal of each of the differential amplifiers is commonly connected, a bias voltage is applied to a second input terminal of the first differential amplifier, and a bias voltage is applied to a second input terminal of the first differential amplifier. A second differential amplifier configured such that second and first output terminals are commonly connected, and first and second output terminals of the first and second differential amplifiers are commonly connected and connected to a power supply. a third differential amplifier having a first and second input terminal, a first and second output terminal, and a bias current input terminal, the third differential amplifier having a bias current input terminal; terminal is connected to a current source, first and second output terminals are connected to respective bias current input terminals of the first and second differential amplifiers, and further between the first and second input terminals a second circuit section configured to apply a DC control voltage; and a second circuit section configured to apply a DC control voltage;
and a parallel resonant circuit whose one end is connected to the commonly connected second and first output terminals of the second differential amplifier and whose other end is connected to a constant potential, and the voltage of this parallel resonant circuit or its level. A series circuit of two impedance elements connected in series to the parallel resonant circuit to generate two voltage components with different phase angles than the shifted voltage, and one of the two voltage components obtained by this series circuit. to a second input terminal of the second differential amplifier, and means for feeding back the other one to the commonly connected first input terminals of the first and second differential amplifiers. Features a voltage controlled oscillation circuit. 2 comprising first and second differential amplifiers each having a first and second input terminal, a first and second output terminal, and a bias current input terminal, each of the first and second differential amplifiers a first input terminal of the first differential amplifier is connected in common and a bias voltage is applied to a second input terminal of the first differential amplifier; a first circuit section configured such that the two output terminals are commonly connected to a power supply, and the bias current input terminals of the first and second differential amplifiers are respectively connected to a current source; , first,
third and fourth differential amplifiers each having a second input terminal, first and second output terminals, and a bias current input terminal, the first and second input terminals of the third differential amplifier; A DC control voltage is applied between the first and second input terminals, and the first and second input terminals of the fourth differential amplifier are commonly connected, and the third and fourth differential amplifiers are connected in common. The first and second output terminals of the differential amplifiers are commonly connected, and the second and first output terminals of the third and fourth differential amplifiers are commonly connected and connected to a power supply. A parallel circuit in which one end is connected to the commonly connected first and second output terminals of the third and fourth differential amplifiers and the other end is connected to a constant potential. a series circuit of a resonant circuit and two impedance elements connected in series to the parallel resonant circuit so as to generate two voltage components having different phase angles than the voltage of the parallel resonant circuit or a voltage obtained by level-shifting the voltage of the parallel resonant circuit; , one of the two voltage components obtained by this series circuit is connected to the second input terminal of the second differential amplifier, and the other one is connected to the common connection of the first and second differential amplifiers. A voltage controlled oscillator circuit comprising means for feeding back to a first input terminal.