JPS6214724Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature compensation circuit for an oscillation circuit suitable for use, for example, in temperature compensation for a local oscillation circuit of a receiver.

Recently, it has become common practice to incorporate part or all of a circuit configuration into an IC and house it in a single package. Figure 1 shows an example of the high frequency stage and intermediate frequency stage of a radio receiver. The stored IC package cage 1 is shown. 2 shows the tuning circuit part of the external local oscillation circuit, 3 is a coil, 4 is a variable capacitance element, 5 is a trimmer capacitor,
Although not shown, 6 is a capacitor connected to the base of an amplifier element, such as a transistor, of the local oscillation circuit. Depending on the tuning operation, the capacitance of the variable capacitance element 4 changes due to the tuning voltage supplied from the input terminal 7,
Eventually, the local oscillation frequency changes to a frequency corresponding to the receiving frequency to be tuned, and tuning becomes possible.

Further, temperature compensation of the tuning circuit 2 is normally performed by connecting a temperature compensation capacitor 8 in parallel with the variable capacitance element 4.

These package 1 and tuning circuit 2 are combined with a low frequency stage (not shown) and housed in a case to complete one set.If you look at the change in the internal temperature of the set in the power supply bag, As shown by curve A in Figure 2, it gradually rises over time t ₂ (approximately 30
quantile) to reach a constant temperature.

Therefore, conventionally, in response to this temperature change, the capacitor 8 compensates for the temperature of the tuning circuit 2, that is, the change in the local oscillation frequency.

However, although it varies somewhat depending on the IC, the internal temperature of the IC package 1 differs between the initial state after power-on and after a certain time t ₁ (approximately 2 minutes), as shown by curve B in Figure 2. There is a problem that the local oscillation frequency changes.

This is because as the temperature of the IC pellet changes, the base-collector capacitance C _pb of the transistor that makes up the oscillation circuit changes and the oscillation frequency changes, or the base-emitter voltage V _BE changes as the temperature changes.
It is thought that the oscillation frequency changes as the bias conditions change.

Therefore, the conventional method of temperature compensation by simply connecting the temperature compensation capacitor 8 in parallel with the variable capacitance element 4 is effective for temperatures that change uniformly, such as the internal temperature of the IC package. It has the disadvantage that it does not follow rapidly changing local temperatures such as temperature, and the local oscillation frequency changes, deteriorating the characteristics of the receiver.

The present invention has been devised in view of these points, and provides a temperature compensation circuit for an oscillation circuit that can compensate for both the internal temperature of the set and the internal temperature of the IC package, and can always obtain a stable oscillation frequency.

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4.

FIG. 3 shows the configuration of this embodiment. In FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, temperature compensation capacitors 8a and 8b each having a value equivalent to the divided capacitance of the temperature compensation capacitor 8 used in FIG. 1 are provided, and the capacitor 8a is connected in parallel to the variable capacitance element 4 as described above. , the capacitor 8b is fixed to one surface of the IC package 1 with a thermally conductive adhesive 9.

And IC package 1 is connected by capacitor 8b.
The temperature rise inside the package conducted to the outside of the package is detected, and the capacitance change is transmitted to the tuning circuit 2 to correct the local oscillation frequency accordingly. Also, compensation for the temperature inside the set is performed by a capacitor 8a.
Of course, since the capacitor 8b is exposed inside the set, it also serves as temperature compensation inside the set together with the capacitor 8a.

Figure 4 shows the change in local oscillation frequency after power-on in comparison with a conventional circuit. In the conventional circuit, as shown by the broken line in the figure, the initial state after power-on, that is, time t ₁ (approximately 2 minutes) Although the local oscillation frequency changes significantly due to the influence of temperature rise during the period of time, the temperature compensation method described above is used in this embodiment, so that even in the initial state, as shown by the solid line in the figure, the influence of temperature rise is almost negligible. It can be seen that a substantially constant local oscillation frequency can be obtained without being affected by the noise. By the way, in the initial state, the conventional circuit has a frequency of 8kHz around 4~7MHz and 9.5~18M.
There was a frequency drift of 18 kHz near Hz, but in this example, it was significantly improved to 2 kHz and 4 kHz, respectively, at the same frequency.

As described above, according to the present invention, since the capacitors 8a and 8b simultaneously compensate for the effects of the internal temperature of the set and the internal temperature of the IC package, it is possible to always obtain a constant and stable oscillation frequency regardless of temperature changes. Unlike the conventional method, the characteristics of the receiver etc. are not deteriorated.

Although the above-mentioned embodiment describes the case where the present invention is applied to a radio receiver, the present invention is not limited to this and can be similarly applied to other devices that use an IC-based oscillation circuit. Not even.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a conventional circuit, Figure 2 is a characteristic diagram for explaining the operation of Figure 1, and Figure 3 is a diagram showing an example of a conventional circuit.
FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a characteristic diagram showing a comparison of frequency drift between the circuit according to the present invention and a conventional circuit. 1 is IC package, 2 is tuning circuit, 8a, 8
b is a temperature compensation capacitor, and 9 is a fixing material.

Claims (1)

[Scope of utility model registration request] A capacitive element of an oscillation tuning circuit externally attached to an IC incorporating a local oscillation circuit, a first temperature compensation capacitive element connected in parallel to this capacitive element and detecting a temperature rise inside the set, and the above-mentioned capacitor. A temperature compensation circuit for an oscillation circuit, characterized in that a second temperature compensation capacitive element is connected in parallel to the IC element and is attached to the package of the IC to detect a temperature rise inside the package.