JPS6112105A - Lc oscillation circuit - Google Patents

Abstract

PURPOSE:To decrease the characteristic change in an oscillating frequency against variance in Q of an LC resonance load by adding a diode to a transistor (TR) forming a differential circuit. CONSTITUTION:A diode 19 is added between a reference potential point of a positive pole of a power supply 11 and a collector of a TR15. That is, the LC oscillating circuit uses the diode 19 to bring the TR15 to a saturated region in the control range of a control current I. In this case, a voltage capacity VF of the diode 19 is set smaller than a base-emitter voltage VBE of the TR15. This is because the degree of the saturation of the TR15 is larger as the VF approaches more the VBE and the change in the oscillating frequency is increased. Through the forming above, the characteristic change in the oscillating frequency is reduced against variance in the Q of the LC resonance load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an LC oscillation circuit whose oscillation frequency can be controlled by current or voltage.

[Technical background of the invention and its problems] In general, an LC oscillation circuit is used as an integrated circuit (hereinafter abbreviated as IC) in an electronic circuit such as a PLL (phase synchronization control) circuit or a local oscillation circuit of a receiver. As shown in FIG. 5, it is constructed of a differential type. That is, in this LC oscillation circuit, when the power supply 11 is turned on and a current is supplied to the current source 12, this current is input to the current mirror circuit consisting of transistors 13 and 14, converted to the collector current of transistor 4, and then supplied to transistor 15. .16, is output to the common emitter section of the differential oscillation circuit consisting of the capacitor 7 and the coil 18.

In other words, in the above differential oscillation circuit, the transistors 15, 1
6 is operating without entering the saturation region, the oscillation frequency f osc is determined by (C: the capacitance of the capacitor 7, L: the filter 18 inductance).

However, when the transistor 16 operates in the saturation region, the base-collector of the transistor 16 is biased in the forward direction, and the isometric (feedback) capacitance between the base and collector increases significantly compared to when it is reverse-biased. However, the oscillation frequency f osc becomes lower than the above calculated value. For example, if the voltage of the power supply 11 is 5LVl, the capacitor 17
The capacitance C of the coil 18 is set to 190 [PF], the inductance L of the coil 18 is set to 560 [μH], and the collector current of the transistor 14 (control current I) is changed by changing the current amount of the current source 12.
When the oscillation frequency f osc is measured when changing the oscillation frequency f osc , the result is as shown in FIG.

In other words, from this FIG. 6, the capacitor 17 and the coil 1
When the Q of the LC parallel resonant load consisting of 8 is low, the transistor 16 does not enter the saturation region, so the oscillation frequency
osc hardly changes from 40 to 140 [μA], but if the Q of the parallel resonant load is high, the control current I
It can be seen that the signal amplitude appearing across the parallel resonant load increases in accordance with an increase in , and as a result, the transistor 1G enters the saturation region and the oscillation frequency f O20 decreases. That is, by setting the Q of the LC parallel resonant load to be high, a current control type LC oscillation circuit can be constructed.

However, in the conventional LC oscillation circuit as described above,
When an LC parallel resonant load is integrated into an IC, its Q tends to vary, and as described above, the characteristics of the oscillation frequency f osc also vary in accordance with the variation in Q.

[Object of the invention] This invention improves the above problems! The object of the present invention is to provide an LC oscillation circuit that can reduce changes in oscillation frequency characteristics due to variations in Q of a C resonant load.

[Summary of the Invention] In other words, an LC oscillation circuit according to the present invention includes a differential circuit including a pair of transistors, a current source that controls the amount of current flowing through the differential circuit, and one transistor of the pair of transistors. An LC resonant load consisting of a capacitor and a coil is interposed in the current supply path, and a diode is interposed in the current supply path of the other transistor of the pair of transistors and operates the other transistor in a saturated state within a control range. It is characterized by:

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to FIGS. 1 and 2. However, in FIG. 1, the same parts as in FIG. 5 are designated by the same reference numerals, and only the different parts will be described here.

FIG. 1 shows its configuration, in which a diode 19 is interposed between the reference potential point on the positive electrode side of the power source 11 and the collector of the transistor 15.

In other words, in this LC oscillation circuit, the diode 19 causes the transistor 15 to enter the saturation region within the control range of the control current I. In this case, the voltage capacity IMF of the diode 19 is the voltage between the base and emitter of the transistor 15. Set smaller than voltage VBE. This means that VF is VB
This is because the closer to H, the greater the degree of saturation of the transistor 15 becomes, thereby making it possible to increase the change in the oscillation frequency fosc. However, if it gets too close, the transistor 15 will be completely saturated and the oscillation will stop.

In FIG. 2, the power supply 11 is similar to the case shown in FIG.
The voltage is 5 [V], and the capacitance C of the capacitor 17 is 190 [V].
PF], the inductance L of the coil 18 is 560 [μH
] and shows the results of measuring the oscillation frequency f osc when the collector current (control current I) of the transistor 14 was changed by changing the amount of current of the current source 12. It can be seen from FIG. 2 that this LC oscillation circuit exhibits less characteristic change in the oscillation frequency f with respect to variations in the Q of the LC parallel resonant load than the conventional one. Furthermore, it can be seen that the oscillation frequency f osc changes linearly even if the Q of the LC parallel resonant load changes with respect to the change in the control current I.

Therefore, the C oscillation circuit configured as above is L
This makes it possible to reduce changes in the oscillation frequency characteristics due to variations in the Q of the C resonant load.

FIG. 3 shows another embodiment of the present invention, in which transistors 20. [1 shows the case where the polarity is opposite to that of the transistors 15 and 16 of the embodiment shown in FIG. Note that the current source 22 is equivalent to the current source made up of the current source 12 and transistors 13 and 14. The operation of this LC oscillation circuit is the same as that of the previous embodiment, so its explanation will be omitted.

FIG. 4 shows a configuration in which the LC oscillation circuit 23 shown in FIG. The oscillation signal is amplified by an amplifier circuit 24 consisting of Q4, diodes DI, D2, and current source 1, and output to 12L via an output terminal 25.
The signal is supplied to the frequency dividing circuit 26. In other words,
This PLL multiplexer circuit is easy to integrate into an IC,
Since there is little change in the characteristics of the oscillation frequency f osc of the LC oscillation circuit, the accuracy is extremely high.

In this way, the LC oscillation circuit according to the present invention is applicable to various electronic circuits.

[Effects of the Invention] As described above, according to the present invention, the L
A C oscillation circuit can be provided.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the LC oscillation circuit according to the present invention, Fig. 2 is a characteristic diagram showing the characteristics of the oscillation frequency with respect to the control current of the same embodiment, and Figs. FIG. 5 is a circuit diagram showing the configuration of a conventional LC oscillation circuit, and FIG. 6 is a characteristic diagram showing the frequency characteristics of the LC oscillation circuit. 11...Power supply, 12. ...Current source, 13-16...
- Transistor, 17... Capacitor, 18... Coil, 19... Diode, ■... Control current. Applicant's agent Patent attorney Takehiko Suzue Figure 3 Figure 4

Claims (1)

[Claims] a differential circuit made up of a pair of transistors, a current source that controls the amount of current flowing through the differential circuit, and an LC resonant load made of a capacitor and a coil interposed in the current supply path of one of the pair of transistors; An LC oscillation circuit comprising: a diode that is interposed in a current supply path of the other transistor of the pair of transistors and causes the other transistor to operate in a saturated state within a control range.