JPH0656931B2 - Oscillator - Google Patents

Description

The present invention relates to an oscillating device, and an object of the present invention is to provide an oscillating device that can stably oscillate even if deviations of various circuit element constants are large.

Oscillators are used in various receivers, but it is necessary that the oscillators always oscillate stably.
If stable oscillation does not occur due to the value or deviation of the active element or passive element, it becomes necessary to limit the element constant, resulting in an oscillation device with narrow manufacturing conditions for stable operation, which is extremely difficult to build. turn into.

FIG. 1 and FIG. 2 are diagrams showing a conventional example of an oscillator having a configuration intended to be a semiconductor integrated circuit (IC). In FIG. 1, reference numerals 1 and 2 denote transistors of a differential pair, which is the main constituent of the oscillator, 3 is a constant current source, 4 is an external terminal for oscillation, 5 is a coil, 6 is a capacitor, and a coil 5 and a capacitor 6 are provided. And constitute an LC parallel resonance circuit. And
Reference numeral 7 is an equivalent parallel resistance component of the resonance circuit, 8 is a power supply terminal for supplying a power supply voltage, and 9 is a ground potential power supply terminal. When the oscillator is integrated into an IC, the frame 1 indicated by a chain line
The circuit portion within 0 is built in a single semiconductor substrate.

By the way, in this oscillator, if a slight shock voltage is applied to the base of the transistor 1 or the base of the transistor 2 in some form, the potential of the external terminal 4 for oscillation is equal to the inductance L of the coil 5 and the capacitor 6. It fluctuates according to the response determined by the capacitance C, and acts to further strengthen the base potential difference between the transistors 1 and 2 generated earlier, and the oscillation phenomenon is repeated.

The oscillation frequency fosc at this time is It is well known that However, the load of the transistor 1 is the resonance circuit of the coil 5 and the capacitor 6 and the equivalent parallel resistance component 7, and once the oscillation device causes an oscillation phenomenon, the load becomes a sufficiently large value in terms of AC, but is stationary. In this state, the DC resistance of the coil 5 (the resistance that determines the Q of the coil) is very small, so the DC voltage gain is also small. Therefore, when the shock is small, the oscillation phenomenon does not occur and the oscillation remains stopped.

FIG. 2 shows an oscillator in which a resistor 11 (R ₁₁ ) is inserted to increase the DC voltage gain, and the drawbacks of the oscillator shown in FIG. 1 are eliminated. By the way, in this oscillator, if the current flowing through the transistor 1 is I _E1 , the potential difference ΔV _BE between the bases of the transistor 1 and the transistor 2 is ΔV _BE = I _E1 R
₁₁ , and the value of ΔV _BE must be set so as not to deviate from the active region of the differential amplifier formed by the transistors 1 and 2. Here, it is I _E and R ₁₁ that determine the DC voltage gain, and it is the impedance at resonance of I _E and L, C and the value r of the equivalent parallel resistance component 7 that determines the oscillation amplitude. , I _{E and} the deviation of I _E , R ₁₁ ,
Considering the temperature characteristics of L and C, each element must be used in a limited manner.

In the circuit of FIG. 2, the selectivity Q of the parallel resonant circuits 5 and 6
Is found to affect the stable oscillation operation, and the resistance is intentionally inserted to experimentally determine the effect of the equivalent parallel resistance 7 in FIG. The broken line in FIG. 3 shows the data obtained by gradually increasing the value from 0 and plotting the value rmin at the start of oscillation against the value of R ₁₁ . The broken line in FIG. 3 shows that rmin is small near R ₁₁ = 100 to 150Ω and oscillates most easily, and when R ₁₁ is larger than that, oscillation is rather difficult. This is because the above-mentioned ΔV _BE increases at an accelerated rate with the increase of R ₁₁ , and when I _E = 0.2 mA, ΔV _{BE is 30} mV when R ₁₁ = 200Ω, and the operation at the margin of the active area of the differential amplifier is performed. This is because the gain is significantly reduced.

As can be seen from this example, the conventional circuit configuration shown in FIG. 2 has a drawback that the differential amplifier is out of balance while the DC gain increases, and it must be used at a compromise point, and variations in the circuit element constants. , I _E deviation, temperature variation, etc. are extremely difficult to use, and in an integrated circuit or the like, the allowable variation range of process parameters is narrow, and the manufacturing yield is poor.

The present invention has been made to eliminate the inconveniences of the conventional examples described above, and provides an oscillation device that oscillates extremely stably and does not reduce the manufacturing yield when integrated into an IC.

The oscillator of the present invention will be described in detail below with reference to FIG. FIG. 4 is a diagram specifically showing a configuration example of the oscillator of the present invention. The basic configuration is the same as that of the conventional oscillator shown in FIG. 1 and FIG. The difference is that the common connection point between the base of the transistor 1 and the collector of the transistor 2 is connected to the V _CC line in which the voltage V. With such a configuration, the fact that the DC voltage gain, which is a drawback of the configuration of FIG. 1, is eliminated by adding the resistor 11, and the value of ΔV _BE , which is a drawback of the configuration of FIG. Is removed from the active region of the differential amplifier by adding the resistor 12. Therefore, the values of the coil 5 and the capacitor 6 need not be particularly considered.

In the circuit of FIG. 4, when the value r of the equivalent parallel resistance component is gradually increased from O and turned over, the value rmin at which oscillation starts
Data plotted with respect to the value of R ₁₁ is shown by a solid line in FIG. 3 as in the case of the conventional example. The measurement conditions and external L, C, etc. are the same as in the conventional example shown by the broken line.

That is, in the oscillator of the present invention, since the DC load of the differential amplifier is balanced by adding the resistor 12, the DC operating point is always set at the center of the active region, and the reduction of DC gain is prevented. Has been. Therefore, the values R ₁₁ and R ₁₂ of the resistors 11 and ₁₂ are increased to, for example, 200
Even if the value is in the vicinity of Ω, no increase in rmin is seen as in the case of the conventional oscillator shown by the broken line, and the oscillation occurs at an extremely small value of r.

Thus, by adding the resistor R ₁₂ having the same value as the resistor R ₁₁ , an extremely stable oscillation circuit can be constructed.

Further, in the conventional oscillator shown in FIG. 2, as is apparent from FIG. 3, the allowable range of the optimum value of R ₁₁ (the portion in FIG. 3A) is not so wide. For this reason, when the circuit IC is formed, it is not possible to use an IC resistor having a large variation in value and a large variation in value due to temperature, and an external resistor is used. On the other hand, in the oscillator of the present invention, it is sufficient to establish the relationship of R ₁ R ₂ between the values R ₁₁ and R ₁₂ of the resistors 11 and 12, and the allowable range of the absolute value of R ₁ and R ₂ itself. (Fig. 3B part) is extremely wide. Therefore, the above IC resistor can be used, and the third
As shown in the figure, the resistors 11 and 12 can be housed inside a circuit portion that can be integrated into an IC, and the number of externally attached portions when integrated into an IC can be reduced.

SUMMARY OF THE INVENTION The present invention is summarized as follows: a transistor of a differential pair comprising first and second transistors 1 and 2 having emitters commonly connected and collectors and bases cross-connected to each other; and a collector of the first transistor 1. External terminal 4 for oscillation
And a second resistor 12 connected between the collector of the second transistor 2 and the power supply terminal 8, the first resistor 11 connected between 1, 2 and the first and second resistors 11 and 12 are integrated into an IC
The oscillating device is characterized in that an LC parallel resonance circuit (5, 6) is connected between the external terminal 4 and the power supply terminal 8 while being integrated inside, and the oscillating device is summarized as follows. It is easy to start by increasing the DC load of the oscillator circuit, the operating points of the transistors of the differential pair are kept balanced, and it operates stably even if the resistance value varies. In addition, since one terminal connecting the resonance circuit can be shared with the power supply terminal, only one external terminal connects the resonance circuit. It has a special effect that it oscillates stably without depending on the absolute accuracy of.

[Brief description of drawings]

1 and 2 are circuit diagrams showing a configuration example of a conventional oscillator, FIG. 3 is a characteristic diagram showing a relationship between a load resistance and a minimum equivalent parallel resistance value for starting oscillation, and FIG. 3 is a circuit diagram showing a circuit configuration of the oscillator of FIG. 1, 2 ... Differential pair transistors, 3 ... Constant current source, 4
... external terminal for oscillation, 5 ... coil, 6 ... capacitor, 7 ... equivalent parallel resistance of resonant circuit, 8 ... power supply terminal,
9 ... Ground terminal, 10 ... IC circuit part, 11, 12 ...
…resistance.

Claims (1)

[Claims] 1. A differential pair of transistors comprising first and second transistors having emitters commonly connected and collectors and bases cross-connected to each other; a collector of the first transistor and an external terminal for oscillation. A first resistor connected between the first transistor and a second resistor connected between a collector of the second transistor and a power supply terminal, and the first and second transistors and the first and second transistors. An oscillator, wherein a second resistor is integrated inside the IC, and an LC parallel resonance circuit is connected between the external terminal and the power supply terminal.