JPS6022845B2 - voltage controlled oscillator - Google Patents

Description

[Detailed description of the invention] The present invention relates to voltage controlled oscillators.

An example of a conventional technique will be explained with reference to FIG. Connect the base and collector to the collector of the other transistor.
The emitters of transistors 1 and 2 connected to the current source 3 are commonly connected and connected to a current source 3. The collector of the transistor 1 is directly connected to the power supply terminal 4, and the collector of the transistor 2 is connected to the power supply terminal 4 through a parallel resonant circuit consisting of a coil 5 and a capacitor 6. The collector of the transistor 2 is connected to a variable capacitance diode 8 through a capacitor 7, and the other side of the variable capacitance diode is connected to GND (ground terminal) 9. A control input terminal 10 is connected through a resistor 11 to a connection point between the capacitor 7 and the variable capacitance diode 8. The oscillation frequency momme sc of this voltage controlled oscillator is bSCni.
/2 level L (C + CD) ... is given by {1).

However, C7》Co. R,. 》2mfoscL. C:
Capacity of capacitor 6, CD: Capacitance of variable capacitance diode 7, R, . : Size of resistor 11.

Here, the capacitance C of the variable capacitance diode 8.

can be changed by the control input voltage, so the oscillation frequency can be changed. As mentioned above, conventional voltage controlled oscillators using a resonant circuit composed of a coil and a capacitor have used variable capacitance diodes to change the oscillation frequency.
However, this circuit configuration requires a large capacitance change width of the variable capacitance diode, linearity of the capacitance change with respect to the control width, and Q characteristics as a tuning capacitor, which increases the cost and makes it difficult to integrate the circuit. There was a drawback in the structure.
In order to eliminate these drawbacks, the present invention constructs a voltage controlled oscillator with a circuit that has good linearity of control characteristics with respect to the oscillation frequency, has a wide variation range, and is easy to integrate into an integrated circuit without using a variable capacitance diode. It is.

The present invention will be explained using the drawings.

As shown in FIG. 2, the emitters of transistors 1 and 2, each having its base connected to its collector, are commonly connected and connected to a variable current source 12.

The collector of transistor 1 is directly connected to power supply terminal 4,
The collector of the transistor 2 is connected to the power source 4 through a parallel resonant circuit consisting of a coil 5 and a capacitor 6. The magnitude of variable current source 12 can be changed by input from control input terminal 10. Next, it will be shown that the oscillation frequency of this circuit depends on the current value of the variable current source 12. Figure 3 is the second
This is an equivalent circuit diagram for calculating the oscillation frequency of the oscillation circuit shown in the figure, in which transistors 1 and 2 whose bases are connected to each other and their collectors are connected to a common emitter are represented as a hybrid type equivalent circuit.

Terminals 13, 14 and 15 correspond to the collector, base and emitter terminals of transistor 1, respectively;
6, 17 and 18 correspond to the collector, base and emitter terminals of transistor 2, respectively. Also, the base resistances of transistors and 2 are equivalent resistances 19 and 2.
0, the input resistance is shown by the equivalent resistances 21 and 22, and the depletion layer capacitance of the emitter and base junctions is shown by the equivalent capacitances 23 and 2.
4. The emitter diffusion capacitance is equivalent capacitance 25 and 26, and the collector and base junction depletion layer capacitance is equivalent capacitance 27 and 2.
8, auxiliary power supplies are shown at 29 and 30, respectively. During steady oscillation, the loop gain is as small as 1, and the depletion layer capacitances 27 and 28 at the collector and base junctions are small, so they can be ignored.

Also, based on the symmetry of the circuit, if we rewrite Figure 3, we get the equivalent circuit No. 4.
Get the picture. Here, find the impedance between the collectors of transistor and 2.
‐‐‐■ However, fT》Z: Impedance between the collectors of transistor and 2, L: Impedance of coil 5, C: Capacity of capacitor 6, Cb: Sum of capacitances of equivalent capacitance 23 and equivalent capacitance 25, two equivalents. Sum of capacitances of capacitance 24 and equivalent capacitance 26, rb: Value of equivalent resistances 19 and 20, r stroke: Value of equivalent resistances 21 and 22, fT: i8! = 1 frequency, B: Emitter grounded current amplification factor.

At the oscillation frequency, Z becomes a pure resistance with zero phase angle, so (
Assuming that the imaginary part of Z)=0, {31 equation is obtained.

1 4 fOSCCb
r light 2 futaki left = 2 fosCC 10
...{3} From this, the oscillation frequency can be found. sc: oscillation frequency, k: Bormann constant, q: electron charge, T:
Absolute temperature, lo: magnitude of current of variable current sources 1 and 2, where f,》phantom sc, C》Cb, r　》rb.

becomes. The above formula (■) is the magnitude of the current of the variable current source 12 lo
This shows that the oscillation frequency can be changed by changing . As explained above, according to the present invention, since the oscillation frequency can be changed by changing the magnitude of the current of the variable current source 12, there is no need to use a variable capacitance diode, which has the effect of facilitating integration into an integrated circuit.

Further, as shown in equation '4', the change in the oscillation frequency is proportional to the magnitude lo of the current of the variable current source 12, which has the effect of improving the linearity of the control characteristic of the oscillation frequency. Because of the excellent features described above, when the present invention is used as a voltage controlled oscillator in a phase-locked circuit for FM detection or PM detection, a detection circuit with small detection distortion can be realized.

FIG. 5 is a circuit connection diagram of a specific embodiment of the present invention.

A transistor 30 is formed by connecting the emitters of transistors 1 and 2 in common, with their bases connected to their collectors.
Connect to the collector of

The outside of the transistor 1 is directly connected to the power supply terminal 4, and the collector of the transistor 2 is connected to the coil of a parallel resonant circuit composed of a coil 5 and a capacitor 6 with an intermediate connection point, and one end of the parallel resonant circuit is connected to the power supply terminal 4. followed by The base of the transistor 31 is connected to the control input terminal 10, and the emitter is connected to the GND terminal 9 through a resistor 32. The base of the transistor 33 is connected to the collector of the transistor 2, the collector is connected to the power supply terminal 4, the emitter is connected to the output terminal 34, and the emitter is connected to GND through the resistor 35.
Connect to terminal 9.

The present example shown in FIG. 5 is an example of use as a voltage controlled oscillator in a phase-locked circuit, and in order to prevent the variable frequency width from becoming too wide, an intermediate connection point is provided in the coil 5 of the resonant circuit. If the turns ratio of the entire coil 5 up to the midpoint is 1:m, the tuning capacitance will equivalently be 1/〆 times, so the oscillation frequency will be (〇<m<・) 13,: of the transistor 31. The change in the oscillation frequency due to the collector current is twice as small as that in formula 4.

FIG. 6 shows another specific embodiment of the present invention, which differs from the embodiment described above in that resistors 36 and 37 are connected to the emitters of transistors 1 and 2, respectively.

The oscillation frequency in this case is expressed by the resistance values of the resistors 36 and 37 expressed as Re.

This equation shows that the dependence of the oscillation frequency on the collector current of transistor 31 becomes smaller due to the inclusion of a resistor in the emitter. It has a suppressing effect.

[Brief explanation of drawings]

Figure 1 is a circuit connection diagram explaining a conventional voltage controlled oscillator.
FIG. 2 is a circuit connection diagram of an embodiment of the present invention, FIG. 3 is an equivalent circuit diagram for determining the oscillation frequency of the embodiment, and FIG.
5 is a circuit connection diagram showing a specific embodiment of the present invention, and FIG. 6 is a circuit connection diagram showing another embodiment of the present invention. 1, 2, 31, 33...transistor, 3...current source,
4...Power terminal, 5...Coil, 6,
7. ．．・．． ．．・Capacitor, 8...Variable capacitance diode, 9...GND terminal, 1 0...
Control input terminal, 1 1, 32, 35, 36, 37...
...Resistance, 12...Variable current source, 13, 16
......Collector terminal, 14,17...Base terminal, 15,18...Emitter terminal, 19,20,
21, 22...Equivalent resistance, 23, 24, 25, 26
, 27, 28... Equivalent capacity, 29, 30...
...Dependent current source, 34...Output terminal. Younger brother's picture, crocodile, 2, chicken, 3, crocodile, figure 6, figure 6

Claims (1)

[Claims] 1 first and second transistors whose emitters are coupled to each other, whose bases are connected to the collectors of the other, and whose bases are connected to the collectors of the other;
a resonant circuit connected between the collectors of the first and second transistors; and a current source connected to the emitter coupling point of the first and second transistors, and controls the current value of the current source. A voltage controlled oscillator characterized in that the oscillation frequency is controlled by controlling in response to a signal.