JPH07115377A - Intermediate frequency circuit part - Google Patents

Abstract

PURPOSE:To provide the intermediate frequency circuit part which can evade deterioration of a bit error caused by a drift, even when a band pass filter for inputting an output signal of a frequency mixer and outputting only an intermediate frequency signal is that which drifts a passing frequency band due to its temperature variation. CONSTITUTION:A temperature sensor 10 for detecting a temperature of a band pass filter (ceramic filter) is provided, and also, a relation of a temperature of the above-mentioned ceramic filter and a passing frequency band is stored in advance in a ROM 5e, and by varying a value of a frequency division ratio N of a programmable frequency divider 15a in accordance with a detected temperature of the temperature sensor 10, a frequency of a signal f2 sent to a mixer from a PLL frequency synthesizer 3h is controlled so that the frequency of the output signal from the mixer becomes a center frequency of the frequency band of the temperature sensor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate frequency circuit section in a digital cordless telephone (that is, a personal handyphone).

[0002]

2. Description of the Related Art In recent years, digital cordless telephones, which have become a hot topic, have a circuit configuration as shown in FIG. That is, it includes a transmission / reception antenna 1, a transmission / reception switching circuit 2, a reception unit 3, a signal processing control unit 4, an automatic frequency control circuit 5, a voltage controlled temperature compensation crystal oscillator 6 and a transmission unit 7. Further, the receiving unit 3 includes a low noise amplifier 3a, a frequency mixer 3b which mixes the received signal from the low noise amplifier 3a with the signal f ₁ from the PLL frequency synthesizer 3i serving as the first local oscillator, and outputs the mixed signal. A bandpass filter 3c that selectively passes only a signal in a predetermined frequency band of the output signal of the frequency mixer 3b, and a signal that has passed through this bandpass filter 3c from a PLL frequency synthesizer 3h serving as a second local oscillator. Frequency mixer 3d that mixes and outputs the signal f ₂ of the signal, a bandpass filter 3e that selectively passes only a signal in a predetermined frequency band of the output signal of the frequency mixer 3d, and a bandpass filter 3e that passes the bandpass filter 3e. The amplification circuit 3f that amplifies the output signal by amplifying it with a predetermined amplification factor and the output signal of this amplification circuit 3f , QPSK demodulation to obtain a baseband signal and send it out.

The signal processing control unit 4 for inputting the baseband signal from the receiving unit 3 is a circuit for transmitting various signals and data based on the baseband signal,
For example, the automatic frequency control circuit 5 has frequency error data X
₁ , the transmission / reception switching circuit 2, the transmission / reception switching signal X ₂ , the PLL
The frequency synthesizer 3i receives the frequency setting data X for reception.
₃ , the transmission frequency setting data X ₄ is sent to the PLL frequency synthesizer 7a of the transmitting unit 7. The automatic frequency control circuit 5 has a configuration described later, and the frequency error data X ₁
The voltage-controlled temperature-compensated crystal oscillator 6 is a circuit that outputs a DC voltage based on the above, and supplies a frequency signal corresponding to the output from the automatic frequency control circuit 5 to the PLL frequency synthesizers 3h, 3i and 7a. In addition, the transmitter 7 is
An LL frequency synthesizer 7a, a QPSK demodulator 7b for transmitting a modulated wave signal obtained by modulating the signal from the PLL frequency synthesizer 7a with transmission data from the signal processing control unit 4, that is, a baseband signal, and a bandpass filter 7c.
And a power amplifier 7d.

FIG. 3 shows in detail the main part of the intermediate frequency circuit section comprising the automatic frequency control circuit 5, the voltage controlled temperature compensation crystal oscillator 6 and the PLL frequency synthesizer 3h. That is, the automatic frequency control circuit 5 receives the CP to which the frequency error data X ₁ from the signal processing control section 4 is given.
U5a, ROM 5b and D / A conversion circuit 5c. The CPU 5a takes in the frequency error data X ₁ and executes the processing based on the program in the ROM 5b.
The digital signal corresponding to the frequency error data X ₁ is D /
The digital signal is supplied to the A conversion circuit 5c, and the D / A conversion circuit 5c converts the digital signal into an analog signal and supplies it to the voltage-controlled temperature-compensated crystal oscillator 6. Further, the voltage-controlled temperature-compensated crystal oscillator 6 obtains a signal having a frequency corresponding to the voltage of the given analog signal, and supplies this to the PLL frequency synthesizer 3
to h and so on. Then, in the PLL frequency synthesizer 3h, the frequency divider 11 divides the signal from the voltage-controlled temperature-compensated crystal oscillator 6 by the frequency division ratio M and sends it to the phase comparator 12, which in turn divides it. The phase of the signal from the frequency divider 11 and the signal from the frequency divider 15 are compared, and a pulse output having a pulse width corresponding to the difference between the two phases is transmitted. The low-pass filter 13 gives a voltage component oscillator 14 a DC component voltage obtained by smoothing the pulse output from the phase comparator 12, and the voltage control oscillator 14 gives the signal having a frequency corresponding to the given voltage component. f ₂ is sent to the frequency mixer 3d and also to the frequency divider 15. The frequency divider 15 frequency-divides the sent signal f ₂ by a frequency division ratio N and supplies it to the phase comparator 12. In the so-called lockup state, the frequency divider 15 supplies the signal f ₂ to the phase comparator 12. The frequency of the above-mentioned signal and the frequency of the signal given to the phase comparator 12 from the frequency divider 11 coincide with each other.

[0005]

A frequency mixer 3d for mixing the signal f ₂ from the PLL frequency synthesizer 3h, which is the second local oscillator, with the signal from the bandpass filter 3c (see FIG. 2). As the bandpass filter 3e that selectively passes only the signal of the predetermined frequency band component of the output signal of (3) and sends it to the amplifier circuit 3f, the use of a ceramic filter is being considered because of the possibility of downsizing and weight reduction. However, when a ceramic filter is used as the bandpass filter 3e, the pass frequency band drifts due to the temperature change of the ceramic filter, and as a result, bit error of the received digital data
There is a drawback that the rate deteriorates. The present invention has been made in view of the circumstances as described above, and a bandpass filter that inputs an output signal of a frequency mixer and outputs only an intermediate frequency signal is one in which a pass frequency band drifts due to a temperature change thereof. However, it is an object of the present invention to provide an intermediate frequency circuit section capable of avoiding the deterioration of the bit error rate due to the drift.

[0006]

In order to achieve the above object, the present invention stores temperature detection means for detecting the temperature of a bandpass filter and a relationship between the temperature of the bandpass filter and its pass frequency band. A storage means is provided to determine the current pass frequency band of the band pass filter that has changed due to temperature change, and the local oscillation frequency so that the signal of the center frequency of this pass frequency band is sent from the frequency mixer. The frequency of the signal was adjusted.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to an embodiment shown in the drawings. FIG. 1 shows an automatic frequency control circuit 5, a voltage-controlled temperature-compensated crystal oscillator 6, a PLL frequency synthesizer 3h, etc. in an intermediate frequency circuit section according to this embodiment. This corresponds to FIG. 3 showing the relationship between the control temperature-compensated crystal oscillator 6 and the PLL frequency synthesizer 3h, etc. (Note that in FIG. 1, the circuit part having the same function as the circuit part in FIG. The same reference numerals are used for the parts). In addition, this embodiment is similar to FIG.
Except for the part different from the above, it is exactly the same as the conventional example.

That is, in this embodiment, a temperature sensor 10 for detecting the temperature of the bandpass filter 3e, which is a ceramic filter, is newly added, and the detection output of this temperature sensor 10 is A / of the automatic frequency control circuit 5. The data is supplied to the D conversion circuit 5d, converted into digital data by this, and supplied to the CPU 5f. Also,
The ROM 5e is used not only for the control program but also for the ceramic filter (that is, the bandpass filter 3 in FIG. 1).
It is a circuit unit that fixedly stores the relationship between the temperature and the passing frequency band of e), reads them as appropriate, and sends them to the CPU 5f. The D / A conversion circuit 5c is a circuit unit that converts a digital signal from the CPU 5f into an analog signal and supplies the analog signal to the voltage-controlled temperature-compensated crystal oscillator 6. Further, unlike the conventional example, in the present embodiment, the automatic frequency control circuit 5c is used. CPU 5f
A control signal is sent from the programmable frequency divider 15a of the PLL frequency synthesizer 3h to change the value of the frequency division ratio N of the programmable frequency divider 15a.

In the present embodiment constructed as described above, the temperature of the hand-pass filter 3e shown in FIG. 2, that is, the temperature of the ceramic filter rises while the transmission and reception are repeated, and the pass frequency band of this ceramic filter is increased. When drifting, the temperature sensor 10 shown in FIG. 1 sends a detection output corresponding to the temperature of the ceramic filter to the automatic frequency control circuit 5, that is, the A / D conversion circuit 5d in FIG. Then, the A / D conversion circuit 5d converts the detected output thus sent into a corresponding digital signal, and the CPU 5f
Give to. The CPU 5f receives the frequency error data X ₁ from the signal processing control unit 4 as in the conventional example and sends a corresponding digital signal to the D / A conversion circuit 5c, and this digital signal is sent by the D / A conversion circuit 5c. The signal is converted into an analog signal and given to the voltage-controlled temperature-compensated crystal oscillator 6, and the voltage-controlled temperature-compensated crystal oscillator 6 sends a signal having a frequency corresponding to the voltage of the given analog signal to the PLL frequency synthesizers 3h, 3i, etc. . The CPU 5f performs the following operations in addition to the operations similar to the above-mentioned conventional example. That is, the digital signal (that is, the signal indicating the temperature of the ceramic filter) from the A / D conversion circuit 5d and the ROM
The center frequency fc of the pass frequency band of the ceramic filter at the current temperature is obtained from the data read from 5e (that is, the relationship between the temperature of the ceramic filter and the pass frequency band). Next, the CPU 5f is shown in FIG.
In order to match one frequency of the output signal of the frequency mixer 3d with the center frequency fc, a control signal is sent to the programmable frequency divider 15a of the PLL frequency synthesizer 3h, the value of the frequency division ratio N is changed, and the PLL is changed. The signal f ₂ sent from the frequency synthesizer 3h to the frequency mixer 3d
Change the frequency of. In this case, the voltage-controlled temperature-compensated crystal oscillator 6 is connected to the PLL frequency synthesizers 3i, 7a.
Since there is no change in the frequency of the signal given to, there is no inconvenience in transmission and reception.

When the temperature of the hand-pass filter 3e shown in FIG. 2, that is, the ceramic filter changes and the pass frequency band changes due to the above operation, the frequency of the output signal from the frequency mixer 3d also follows the change. Therefore, the output signal from the frequency mixer 3d is
It can pass through the hand-pass filter 3e, that is, the ceramic filter, and the output signal waveform of the hand-pass filter 3e will not be distorted. As a result, even if there is a temperature change in the ceramic filter, a digital signal that passes through the ceramic filter, is amplified by the amplifier circuit 3f, is demodulated by the QPSK demodulator 3g, and is sent to the signal processing control unit 4 is subjected to the temperature change. There will be no base bit error and no degradation of the bit error rate.

The present invention is not limited to the above embodiment, and various modifications can be applied without departing from the present invention.

[0012]

As described in detail above, the present invention includes temperature detecting means for detecting the temperature of a bandpass filter, and storage means for storing the relationship between the temperature of the bandpass filter and its pass frequency band. , The pass frequency band of the band pass filter after the temperature change is obtained, and the frequency of the local oscillation frequency signal is adjusted so that the signal of the center frequency of this pass frequency band is sent from the frequency mixer. Even if the bandpass filter that receives the output signal of the frequency mixer and outputs only the intermediate frequency signal drifts the pass frequency band due to the temperature change, it is caused by the drift. (EN) It is possible to provide an intermediate frequency circuit unit capable of avoiding deterioration of bit error rate.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional digital cordless telephone.

FIG. 3 is a diagram showing a main part of an intermediate frequency circuit section in a conventional digital cordless telephone.

[Explanation of symbols]

 3d frequency mixer 3e, 13 band pass filter 3f amplifier circuit 3g QPSK demodulator 3h PLL frequency synthesizer 5a, 5f CPU 5b, 5e ROM 5c D / A converter circuit 5d A / D converter circuit 10 temperature sensor 11, 15 frequency divider 12 phase comparator 14 voltage controlled oscillator 15a programmable frequency divider

Claims (1)

[Claims] 1. A local oscillating circuit, a frequency mixer that mixes a transmitted signal with a local oscillating frequency signal from the local oscillating circuit and outputs the signal, and inputs an output signal from the frequency mixer. A bandpass filter that outputs a signal in a frequency band, a temperature detection unit that detects the temperature of the bandpass filter, a storage unit that stores the relationship between the temperature of the bandpass filter and a pass frequency band, and the temperature detection unit. Temperature, the relationship between the temperature and the pass frequency band of the band pass filter stored in the storage means, to determine the current pass frequency band of the band pass filter, the frequency of the output signal of the frequency mixer is Control the frequency of the local oscillation frequency signal sent from the local oscillation circuit so that it becomes the center frequency of the pass frequency band at the present time. Intermediate frequency circuit, wherein the control circuit, in that it comprises that.