JPS6213841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation device that is preferably provided within an integrated circuit.

Recently, it has been considered to incorporate the tuner part of a television receiver into an integrated circuit (IC) including a local oscillator. In this case, the problem is that since a large number of circuits are formed on the same chip, the temperature of the chip increases and a frequency drift occurs in the local oscillator. This problem is particularly noticeable during switch drift from when the TV is turned on until the chip temperature becomes constant.

Conventionally, in general, as a method for stabilizing the oscillation frequency of an oscillation device, first, the coupling between the tank circuit and the transistor is made coarse, so that the oscillation frequency value is determined by the tank circuit as much as possible without depending on the element parameters of the transistor. Consider this. Second, methods such as stabilization using the reactance stabilization method have been used. However, if the tank circuit and transistor coupling are made rough, oscillation tends to become unstable, and although the reactance stabilization method improves at a certain frequency, it is not suitable for tuner oscillation devices that change the oscillation frequency.

This invention was made in view of these points,
It is an object of the present invention to provide an oscillation device that can reduce drift due to chip temperature changes, particularly switch drift, by actively utilizing element parameters of a transistor.

That is, the present invention changes the base-collector junction capacitance of the transistor by changing the base potential of the transistor in an oscillation circuit configured to feed back a part of the collector output of the transistor to the base input side in accordance with temperature changes. This is to reduce drift due to temperature rise.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows the configuration of an oscillation device according to an embodiment of the present invention, which basically consists of an oscillation circuit 1 and a control circuit 2 for reducing temperature drift of this oscillation circuit 1. The oscillation circuit 1 has a first transistor 6 and a second transistor 7 of a differential type, whose emitters are commonly connected to a constant current source 3 and whose bases are connected to bias resistors 4 and 5, respectively. A tank circuit 10 consisting of a reactance L _T 8 and a capacitor C _T 9 is connected between the collectors of the first and second transistors 6 and 7.
Feedback is applied from the collector of the first transistor 6 to the base of the second transistor and from the collector of the second transistor 7 to the base of the first transistor 6 via feedback capacitors 11 and 12, respectively. Note that this oscillation circuit 1 is a tank circuit 1.
0 and feedback capacitors 11 and 12 are integrated circuits. Also, the base of the transistor
The collector-to-collector capacitance C _D is a simulated representation of the junction capacitance.

The oscillation frequency 〓 _SC of this oscillation circuit is expressed by the following formula.

In the above equation, P _TR (T) represents the term due to the element parameters of the transistor excluding the base-collector junction capacitance C _D , and has positive temperature characteristics, so
As the temperature increases, the oscillation frequency decreases. However, as can be seen _from the above equation, the base-collector junction capacitance C _D of the transistor directly affects the oscillation frequency. By reducing , it is possible to keep the oscillation frequency constant with respect to temperature. The control circuit has this function. This control circuit 2
The basic configuration includes a transistor 13 having temperature detection and signal amplification functions and a bias resistor.
It has R ₂₁ , R ₂₂ , R ₂₃ and R ₂₄ and is integrated with the oscillation circuit 1 on the same semiconductor substrate. The base of transistor 13 is a bias resistor
It is connected to the power supply V _CC via R ₂₁ 14 and grounded via bias resistor R ₂₂ 15.
The collector is connected to the power supply V _CC through the bias resistor R ₂₃ 16, and the emitter is connected to the bias resistor R ₂₄
It is grounded via 17. The output is taken out from the collector 18 and connected to the control input terminal 19 of the oscillation circuit 1.

In this circuit, the output potential V _B immediately after turning on the switch is V _B =V _CC -R ₂₃ ×I _Q3 (T ₁ ) (2). However, I _Q3 (T ₁ ) is the current value flowing through the transistor 13 when the chip temperature is T ₁ immediately after switching on, and I _Q3 (T ₁ )=V _C −V _BE (T ₁ )/R ₂₄ (3). . V _C is the base of transistor 13 (C
The bias potential at point ) does not vary with temperature. Further, V _BE (T ₁ ) is the base-emitter voltage of the transistor 13 at the temperature T ₁ .

Next, when the chip temperature rises and becomes constant at T ₂ , the current value I _Q3 (T ₂ ) flowing at that time is I _Q3 (T ₂ )=V _C −V _BE (T ₂ )/R ₂₄ (4) ) becomes. It is known that the base-emitter voltage V _BE of a transistor decreases as the chip temperature rises, and generally has a temperature characteristic of about -2 mV/°C. Therefore, from this temperature characteristic, V _BE (T ₂ ) <
Since V _BE (T ₁ ), I _Q3 (T ₂ )>I _Q3 (T ₁ ). Therefore, from equation (2), the output voltage V _B when the temperature is T ₂ is a lower voltage than when the temperature is T ₁ . Therefore, as the temperature rises, the base potential of the transistors 6 and 7 constituting the oscillation circuit 1 decreases, and the junction capacitance C _D decreases, making it possible to compensate for the decrease in the oscillation frequency.

FIG. 2 shows the measurement results of temperature drift when such an oscillation device is used as a VHF band local oscillation device and a tuner is integrated into an IC. The oscillation frequency is approximately
At 270MHz, the power consumption of the chip is approximately 300mW, and the chip temperature rises approximately 50°C relative to the outside air. In the figure, the solid line A shows the characteristics of the conventional oscillation device in which the base voltage of the transistor is kept constant with respect to temperature rise, and the broken line B shows the characteristics of the oscillation device of the present invention in which the base voltage is lowered by about 1 V with respect to temperature rise. This shows that. As can be seen from this characteristic, in the conventional device without compensation, frequency fluctuations of approximately -160 to 170 KHz appear, whereas in the device of the present invention, frequency fluctuations of approximately -160 to 170 KHz appear.
The fluctuation is suppressed to 50KHz, and the effect of compensation is clearly visible.

FIG. 3 shows a specific example of the configuration of the control circuit 2 used in the present invention. This control circuit is the first
The difference from the configuration of the control circuit 2 shown in the figure is that the first
Transistor 3 corresponding to transistor 13 in the figure
The difference is that a transistor 31 is newly inserted in a Darlington-connected state before the transistor 2. According to this configuration, since there are two V _BEs of the temperature detection section, the bias resistance values R ₃₄ and R ₃₃ are equal to R ₂₄ in Fig. 1.
and R ₂₃ respectively, the output voltage V _B varies by approximately twice. Conversely, to obtain the same output voltage change as with one transistor, the ratio of R ₃₃ /R ₃₄ is R ₂₃ /
The ratio is about half that of R ₂₄ . When diffused resistors are formed in the same chip, the closer the resistance values are, the smaller the variation ratio is, so in this case, a highly accurate control voltage can be created. For the same reason, n transistors 41, 42, . . . can be connected in Darlington as shown in FIG. 4.

FIG. 5 shows still another example of the configuration of the control circuit 2. In FIG. This configuration example differs from FIG. 1 in that a diode 51 is inserted between the base of the transistor 13 and the bias resistor 14 in the forward direction. According to this configuration, the potential at point C is the potential of the diode 51.
Due to the temperature characteristics of , it increases as the temperature rises. Therefore, compared to the circuit of FIG. 1, the apparent temperature coefficient becomes larger by the number of diodes. For this reason, the third
Similar effects can be obtained without providing an extra transistor as in the configuration example shown in FIGS. The temperature coefficient can also be increased by inserting a diode 61 into the emitter of the transistor 13 as shown in FIG.

In oscillation circuits, there is often a requirement to extract the output differentially. In that case, it is necessary to configure the oscillation circuit with a differential transistor pair as shown in Figure 1, but in this case, as the number of transistors increases, the base-collector junction capacitance C _D of the transistor increases. It is desirable that the control circuit has a wide variation range in the output voltage _VB . The control circuits shown in FIGS. 3 to 6 above fully satisfy these requirements.

As described above, the present invention is capable of increasing the oscillation frequency by changing the base potential of the transistor in an oscillation circuit having a tank circuit and configured to feed back a part of the collector output of the transistor to the base. drift can be compensated for.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an oscillation device according to an embodiment of the present invention, FIG. 2 is a diagram showing how frequency drift is improved by the oscillation device of the present invention, and FIGS. 3 to 6 are respectively FIG. 3 is a diagram showing a configuration example of a control circuit used in the oscillation device of the present invention. 1... Oscillation circuit, 2... Control circuit, 3... Constant current source, 6, 7... Transistor, 10... Tank circuit, 13... Transistor, 14, 15, 1
6, 17...Bias resistance.

Claims (1)

[Claims] 1 first and second transistors of differential type whose emitters are commonly connected to a constant current source;
and a tank circuit connected between the collectors of the second transistor and from the collector of the first transistor to the base of the second transistor and from the collector of the second transistor to the base of the first transistor. an oscillation circuit consisting of a feedback circuit that applies feedback, and a control circuit that changes the base potential of the first and second transistors in accordance with temperature changes so as to compensate for changes in oscillation frequency due to temperature changes in the oscillation circuit; The control circuit includes a third transistor, first and second resistors connected between the base and ground of the third transistor and between the emitter and ground, respectively, and the base of the third transistor.・Third and fourth resistors connected between the constant potential and the collector and the constant potential, respectively, and from the third resistor to the second resistor via the base and emitter of the third transistor. at least one diode inserted in the path or at least one transistor Darlington connected to the third transistor;
An oscillation device comprising means for supplying the collector output of the third transistor to the bases of the first and second transistors constituting the oscillation circuit, and the oscillation device is integrated with the oscillation circuit.