JPH04100331A - Cordless telephone set - Google Patents

Abstract

PURPOSE:To quicken the lock time when a channel transfer range is large, to reduce resident FM and to improve the S/N by providing a changeover circuit to the telephone set and selecting a constant of a loop filter in response to the channel transfer range. CONSTITUTION:When a channel transfer width of a reception PLL frequency synthesizer 5 and a transmission PLL frequency synthesizer 6 are small or the synthesizers are in lock state at channel changeover, a control circuit 4 discriminates it and loop filter changeover circuits 8,9 increase a time constant of low pass filters 51,61. When the channel transfer width is large, the control circuit 4 discriminates it and the loop filter changeover circuits 8,9 decrease the time constant of low pass filters 51,61. Thus, the lock time when the channel transfer range is large is quickened and when the channel transfer range is small or in the case of the lock state, the resident FM is reduced and the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a cordless telephone device with an improved frequency synthesizer circuit.

2. Description of the Related Art This type of cordless telephone device consists of a base station connected to a telephone line and a mobile station wirelessly connected to the base station, and uses a multi-channel access method to set up a wireless line for a plurality of wireless channels. This is a device that uses

FIG. 3 shows the configuration of a mobile station of a conventional cordless telephone device.

The mobile station shown in FIG. 3 includes an antenna 11, a receiving circuit 12 and a transmitting circuit 13 connected to the antenna 11. Control circuit 1 connected to receiving circuit 12 and transmitting circuit 13
4 controls the frequency division ratio of the programmable divider 153.163 of the PLL frequency synthesizer 15.16.

The reception PLL frequency synthesizer 15 includes a low-pass filter 151, a voltage controlled oscillator (VCO) 1.52, a programmable divider 153, and a phase detector 154. The transmission PLL frequency synthesizer] 6 includes a low-pass filter 161, a VCO 162, a programmable divider 163, and a phase detector 164. A reference frequency signal from the oscillation circuit 17 is supplied to the phase detectors 154 and 164.

Next, the operation of the above conventional example will be explained.

When a communication channel is set by the control circuit 4, the programmable dividers 153 and 163 are set to a frequency division ratio suitable for the channel. The phase detectors 153.163 output the difference between the reference frequency from the oscillation circuit 17 and the frequency divided by the programmable divider 153.163, and the difference is supplied to the low-pass filters 151.161.

The frequency difference is converted into a DC voltage by low-pass filters 151 and 161, and VCOs 152 and 162 output a frequency corresponding to the voltage.

The transmitting/receiving PLL frequency synthesizers 115 and 116 operate in the direction of eliminating the difference between the reference frequency and the divided frequency, and when the difference disappears, they begin to oscillate a stable frequency (this state is called frequency locked). ).

In this manner, the conventional cordless telephone device described above can oscillate a frequency corresponding to the communication channel by changing the frequency division ratio of the programmable divider 153.163 of the transmitting/receiving PLL frequency synthesizer 115.11-6.

Problems to be Solved by the Invention However, in the above-mentioned conventional cordless telephone device, although the response becomes faster by reducing the time constant of the low-pass filter of the transmitting/receiving PLL frequency synthesizer, the residual FM increases and overshoot is likely to occur when switching channels. There is a characteristic that. On the other hand, in the conventional cordless telephone device, if the time constant of the low-pass filter is increased, residual FM is reduced and overshoot is less likely to occur, but when the channel transition width is large, the response is slow.

In this way, the conventional cordless telephone device has a transmitting/receiving PLL.
Because it has characteristics that conflict with frequency synthesizers,
Fast response even with large channel transition width and residual FM
There is a drawback that it is not possible to design a PLL with a small number of PLLs.

The present invention solves the above-mentioned conventional problems, and provides an excellent cordless telephone device that shortens the lock time when the channel transition width is large, has little residual FM, and has a good S/N ratio. .

Means for Solving the Problems In order to achieve the above object, the present invention comprises a base station connected to a telephone line and a mobile station wirelessly connected to the base station, In a cordless telephone device using a multi-channel access scheme, the station includes a transmitting PLL frequency synthesizer with a loop filter having a plurality of constants;
Receive PLL with loop filter with multiple constants
A frequency synthesizer, a loop filter switching circuit that sets the constant of the rube filter of each of the PLL frequency synthesizers to one, and a loop filter switching circuit that performs channel setting and call connection of each of the PLL frequency synthesizers, and switches and controls the loop filter switching circuit. and a control circuit, wherein the loop filter switching circuit switches a constant of the loop filter according to a channel transition width.

Operation The present invention has the following effects due to the above configuration. That is, the control circuit switches the low-pass filter so that the time constant becomes small when the channel transition width is large, and switches the low-pass filter so that the time constant becomes large when the channel transition width is small.

As a result, lock time is fast, residual FM is small, and overshoot is less likely to occur when switching channels.
It can be a LL frequency synthesizer.

Example Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram showing an embodiment of a mobile station of a cordless telephone device according to the present invention.

The mobile station shown in FIG. 1 includes an antenna 1, and a receiving circuit 2 and a transmitting circuit 3 connected to the antenna 1. The control circuit 4 controls the frequency division ratio of the programmable divider 53 of the reception PLL frequency synthesizer 5. Similarly, the control circuit 4 controls the frequency division ratio of the programmable vibration 63 of the transmitting PLL frequency synthesizer 6. The reception PLL frequency synthesizer 5 includes a low-pass filter 51, a voltage controlled oscillator (VCO) 52, and a programmable vibration generator 5.
3. It is composed of a phase detector 54.

The transmission PLL frequency synthesizer 6 includes a low-pass filter 61, a VCO 62, a programmable waveguide 53, and a phase detector 64. A reference frequency signal from the oscillation circuit 7 is supplied to the phase detectors 54 and 64.

The time constant of the low-pass filter 51 is switched by the loop filter switching circuit 8. Similarly, the low-pass filter 61 also has a loop filter switching circuit 9.
The time constant is switched by .

The loop filter switching circuit 8.9 is turned on and off by a control signal from the control circuit 4.

FIG. 2 is a circuit diagram showing an example of the configuration of the above-mentioned low-pass filter.

Since the low-pass filters 5L and 61 have the same configuration, one configuration will be explained and the other configuration will not be explained.

In FIG. 2, the low-pass filter 51 used in the reception PLL frequency synthesizer 5 is composed of a lag lead filter composed of resistors R, R3 and capacitors C, C2, and a resistor R3 and capacitor C3. It is constructed by connecting a lag filter.

Further, the capacitor C0 is connected in parallel to the capacitor C2 when the transistor Trl constituting the loop filter switching circuit 8 is turned on, and is disconnected from the capacitor C2 when the transistor T is turned off.

Next, the operation of the above embodiment will be explained.

In the above embodiment, the receiving PLL frequency synthesizer 5
The operation of the transmission PLL frequency synthesizer 6 is the same as in the conventional example.

Then, during channel switching operation, if the channel transition width is small or in a locked state, the control circuit 4 determines this and loop filter switching circuit 8.9
As a result, the time constant of the low-pass filters 51 and 61 is increased.

Further, in the channel switching operation, if the channel transition width is large, the control circuit 4 determines this, and the loop filter switching circuit 8.9 reduces the time constant of the low-pass filter 51.610.

As a result, when the receiving PLL frequency synthesizer 5 and the transmitting PLL frequency synthesizer 6 have a small channel transition width or are in a locked state, the response is slow but the residual F
The filter switches to a low-pass filter with a small number of M, and a low-pass filter with a large residual FM but a fast response when the channel transition width is large.

According to the above embodiment, the residual FM in the locked state
This has the advantage that the lock time can be made faster without increasing the signal-to-noise ratio, that is, deteriorating the S/N ratio.

Effects of the Invention As is clear from the above embodiments, the present invention switches to a low-pass filter with a small time constant and quick response when the channel transition width of the PLL frequency synthesizer is large, so that the lock time can be shortened. In addition, when the channel transition width is small or in a locked state, the filter is switched to a low-pass filter with a large time constant and a low residual FM, so that the residual FM is small and the S/N ratio can be improved.

In addition, the present invention does not cause opacity even when the channel transition width is small, and can realize an optimal lock time for any channel transition width.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the cordless telephone device of the present invention, FIG. 2 is a circuit diagram showing a low-pass filter and loop filter switching circuit of the same device, and FIG. 3 is a block diagram showing a conventional cordless telephone device. It is a diagram. l... Antenna, 2... Receiving circuit, 3... Transmitting circuit, 4... Control circuit, 5... Oscillating circuit, 6... Receiving PLL frequency synthesizer, 7... Transmitting PLL frequency Synthesizer, 8.9... Loop filter switching circuit, 51.61... Low pass filter, 52.62
... VCo, 53.63 ... Programmable divider, 54.64 ... Phase detector.

Claims (1)

[Claims] A cordless telephone device comprising a base station connected to a telephone line and a mobile station wirelessly connected to the base station, and using a multi-channel access method to set up a wireless line for a plurality of wireless channels. In the above, the station has a transmitting PLL frequency synthesizer equipped with a loop filter having a plurality of constants, a receiving PLL frequency synthesizer equipped with a loop filter having a plurality of constants, and a constant of the loop filter of each PLL frequency synthesizer. and a control circuit that performs channel settings of each PLL frequency synthesizer, connection of calls, etc., and switches and controls the loop filter switching circuit, and the loop filter switching circuit has a control circuit that controls the switching of the loop filter switching circuit. A cordless telephone device characterized in that a constant of the loop filter is switched accordingly.