JP2969639B2 - Radio selective call receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a local oscillator circuit of a radio selective calling receiver,
In particular, the present invention relates to an improvement in a temperature compensation function of an oscillation frequency of a local oscillation circuit.

[Prior Art] FIG. 6 is a block diagram of a radio selective calling receiver (hereinafter, referred to as a receiver) generally used.

The radio wave transmitted from the base station is received by the antenna 10, amplified by the high-frequency amplifier 20, and frequency-converted by the mixing circuit 40 together with the frequency generated by the local oscillation circuit 30. Generally, the converted frequency is a frequency that can be demodulated, such as 455 kHz. The frequency-converted signal is amplified by the amplifier 50 and converted to a digital signal by the demodulation unit 60.

The ROM 70 stores its own calling number.
At 0, it is determined whether or not the number included in the received data matches the calling number stored in the ROM 70. Control unit
When it is confirmed at 80 that the calling numbers match, a signal is sent to the driving amplifier 100 to make the speaker 110 sound and notify the wearer of the calling.

Reference numeral 90 denotes a crystal oscillator for generating a timing clock of the control unit 80, and reference numeral 140 denotes an operation switch. As the power source 130 of the receiver, a 1.4V battery is usually used. The circuits after the amplifier 50 operate using the battery 130 as a power supply.

The stabilized power supply circuit 120 includes the high-frequency amplifier 20 and the local oscillation circuit.
30, for stably operating the wireless circuit of the mixing circuit 40.

FIG. 7 shows an example of the high-frequency amplifier 20 shown in FIG. The transistors 201 and 202 are cascode-connected, and the resistors 203, 204, and 205 determine the bias of the transistors. The capacitors 206 and 207 are decaps.

FIG. 8 (a) shows an example of the local oscillation circuit 30 shown in FIG. 6, and FIG. 8 (b) is an equivalent circuit thereof, constituting a Colpitts type oscillation circuit. At the oscillation frequency, the coil 30, the crystal oscillator 303, and the trimmer capacitor 304 connected in series are inductive. Meanwhile, coil 3
09 and the capacitor 310 are connected in parallel and are capacitive at the oscillation frequency. The resistors 305 and 306 determine the bias of the transistor, and the capacitors 311 and 308 are decaps.

The deviation of the frequency of the local oscillation circuit mainly occurs due to the deviation of the crystal oscillator 303 and the deviation of the coil 302. The deviation is set to a desired frequency by adjusting the trimmer capacitor 304.

The terminals Ta, Tb, Tc shown in FIGS. 7 and 8 correspond to the terminals Ta, Tb, Tc shown in FIG. The NF of the radio unit is a factor that determines the call sensitivity of the receiver. In FIG. 6, the NF and the gain of the high-frequency amplifier 20 greatly contribute to the NF of the radio unit. That is, a change in the characteristics of the high-frequency amplifier 20 leads to a change in the call sensitivity of the receiver.

FIG. 9A shows the voltage V _BE between the base and the emitter of the transistor 201 used in the high-frequency amplifier 20 shown in FIG.
And generally has a slope of about −2 mV / ° C. As is apparent from this characteristic, when the value of the voltage V _BE changes, the voltage between both ends of the resistor 203 shown in FIG. 7 changes. That is, the base current of the transistor 201 changes, and the NF and gain of the high-frequency amplifier 20 change. For example, at a low temperature, the base current of the transistor 201 decreases due to an increase in the voltage V _BE, so that the N
F and gain decrease. In order to prevent this decrease, the power of the high-frequency amplifier 20 is devised in the receiver.

FIG. 9B shows the temperature characteristics of the power supply of the high-frequency amplifier 20 (corresponding to the power supply of the stabilized power supply circuit 120 in FIG. 6), in which the stabilized power supply voltage V _STB is increased at a low temperature.
The slope of the temperature characteristic in FIG. 9B is the voltage in FIG. 9A.
Since it has the same slope of −2 mV / ° C. as the temperature characteristic of V _BE , the potential at both ends of the resistor 203 in FIG. 7 is constant irrespective of the temperature, that is, the base current of the transistor 201 becomes constant, The properties of 20 are no longer affected by temperature.

The local oscillation circuit 30 shown in FIG. 8 also uses the power supply of the stabilized power supply circuit 120 shown in FIG. 6, but the frequency of the local oscillation circuit 30 has little dependence on the power supply. Depends on characteristics.

 FIG. 10 shows a temperature characteristic diagram of the crystal oscillator 303.

Normally, the operating temperature range of the receiver is -20 ℃ ~ 50 ℃,
The frequency deviation is large around -20 ° C, and in actual use, the standard is set for the deviation at -20 ° C for sorting.

[Problems to be Solved by the Invention] In the above-mentioned conventional local oscillation circuit, since the selection is performed by setting the standard at a low temperature, it takes time and effort for the selection, the yield is reduced, and the cost is increased. Having.

[Means for Solving the Problems] The present invention relates to a radio selective calling receiver having a local oscillation circuit to which a voltage is supplied from a voltage stabilizing means which receives a power supply of an apparatus and outputs a voltage having predetermined characteristics. The temperature compensation of the local oscillation frequency is performed by adding an element whose capacity changes according to the output voltage based on the predetermined characteristic of the voltage stabilizing means to the local oscillation circuit.

[Embodiment] FIG. 1 shows a main part of an embodiment of the present invention, except for the vicinity of a local oscillation circuit 30, which is shown in FIG.

In this embodiment, the varicap 10 is connected in parallel to the trimmer capacitor 304 of the local oscillation circuit 30. Capacitor 1
Numerals 1 and 12 reduce the coupling between the high-frequency amplifier 20 and the local oscillation circuit 30. In general, a high-frequency filter or the like is used instead of the capacitor 11. The coil 18 is for cutting off the AC component.

Next, the relationship between the components of the local oscillation circuit 30, which is the main feature of the present invention, and the oscillation frequency will be described.

First, as shown in FIG. 2, between the trimmer capacitor 304 and the capacitance C of the PQ connected to the varicap 10 and the oscillation frequency f of the local oscillation circuit 30, as the capacitance C increases, the oscillation frequency increases. There is a relationship that f decreases.

FIG. 3 shows the relationship between the applied voltage and the capacitance of the varicap used in the present invention and the change in the capacitance converted into the oscillation frequency.

For convenience of explanation, the stabilized power supply voltages V _STB at normal temperature (25 ° C.) and low temperature (−20 ° C.) are V ₀ and V ₁ respectively, and the capacities of the varicaps 10 at these times are C ₀ and C ₁ , respectively. And Moreover, against the time of the capacitance C ₀ of the varicap 10, the change in the oscillation frequency when a C ₁ to [Delta] F _2.

From the relationship shown in FIG. 2, ΔF ₂ is a positive value. Considering the temperature characteristics of the crystal oscillator in Fig. 10, the oscillation frequency deviation at -20 ° C, which was a problem in the conventional circuit,
(−ΔF ₁ + ΔF ₂ ), and the oscillation frequency shift is improved.

In the present invention, the temperature characteristics of the trimmer capacitor, the coil, and the like are not included, but the degree of improvement ΔF ₂ is the same as that when other temperature characteristics are considered.

FIG. 4 shows an application example of the present invention, in which a transistor is used instead of a varicap. FIG. 5 is a characteristic diagram of the circuit shown in FIG. This example is the base of the transistor - utilizes the capacitance between the collector, Fig. 3 the same characteristics are obtained by a change of the base current I _B. Change of the base current I _B is similar to the case of the varicap, obtained by a change of the stabilized supply voltage V _STB. Further, by using a thermistor in place of the resistor 8, it is also possible to increase the amount of change in the base current I _B at the time of temperature change.

[Effects of the Invention] As described above, the present invention relates to a radio selective call receiver in which a power supply voltage of a radio unit has a temperature characteristic in order to stably operate the radio unit, and to adjust a frequency of a local oscillation circuit thereof. By connecting an element (for example, a varicap) whose capacity varies according to the voltage to the trimmer capacitor in parallel, the temperature characteristics of the frequency of the local oscillation circuit, especially the temperature characteristics at a low temperature (−20 ° C.) are improved. This has the advantage that the standard of the crystal oscillator of the local oscillation circuit can be relaxed and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a radio unit which is a main part of one embodiment of the present invention, and FIG. 2 is a characteristic showing a relationship between a local oscillation frequency and a capacitor connected in parallel to a crystal oscillator according to the present invention. FIG. 3 is a diagram showing the relationship between the applied voltage and the capacitance value of the varicap in the present invention. FIG. 4 is a diagram for explaining the case where a transistor is used instead of the varicap in the present invention. FIG. 6 is a characteristic diagram of the base current-base-collector capacitance of the circuit of FIG. 4, FIG. 6 is a block diagram of a known radio selective calling receiver, and FIG. 7 is a radio selective calling receiver shown in FIG. FIG. 8 is a diagram showing an example of a conventional local oscillation circuit in the radio selective calling receiver shown in FIG. 6 together with its equivalent circuit, and FIG. 9 is a diagram in FIG. Between the base and emitter of the transistor shown Shows the temperature characteristic of the output voltage of the stabilized power supply circuit in the temperature characteristics and the radio selective calling receiver of pressure, Fig. 10 temperature characteristic diagram of crystal oscillator shown in Figure 6. In the figure, 10 is a varicap, 303 is a crystal oscillator, 304
Is a trimmer capacitor.

Claims (1)

(57) [Claims] 1. A radio selective call receiver having a local oscillation circuit to which a voltage is supplied from a voltage stabilizing means which receives a power supply of an apparatus and outputs a voltage having a predetermined characteristic. A radio selective calling receiver, which performs temperature compensation of a local oscillation frequency by adding an element whose capacity changes according to an output voltage based on predetermined characteristics to the local oscillation circuit.