JP3379242B2 - Receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a direct conversion receiver for wireless communication.

[0002]

2. Description of the Related Art Recently, the use of wireless devices such as portable wireless communication devices, telemeter wireless devices used for meter reading of gas, water, and electricity meters, wireless remote controllers for housing equipment, etc. is rapidly expanding. . It is essential that these be made compact and can be installed in any location, and that they be driven by a battery power source for a long time.

Therefore, frequency shift keying (FSK) is used.
A direct conversion receiving device using a ncy sift keying (frequency shift keying) signal has been studied as a configuration suitable for integration into an integrated circuit. By making it an integrated circuit, it is possible to reduce power consumption and size as compared with the conventional double superheterodyne system, and an oscillator and a mechanical filter are reduced in the circuit to facilitate manufacture and adjustment.

For example, the structure described in Japanese Patent Laid-Open No. 58-19038 is known. The direct conversion receiving apparatus will be briefly described below with reference to FIG.

In FIG. 9, the FSK reception signal applied to the antenna input 60 is supplied to the first mixing means 61 and at the same time, supplied to the second mixing means 63 through the 90-degree phase shifter 62, respectively. By mixing with the signal of the signal generating means (local oscillator) 64, the signal is down-converted and data demodulation is performed. The signals output from the first mixing means 61 and the second mixing means 63 include not only baseband signals in the frequency band of 0 to several kHz but also harmonic signals thereof, so that only the baseband signals are passed. The I signal 67 and the Q signal 68 are obtained through the first low pass filter 65 and the second low pass filter 66. The I signal 67 is converted into a digital signal 70 by the amplitude limiting amplifier 69, and the Q signal 68 is phase-shifted by the 90-degree phase shifter 71, and then the digital signal 73 is transmitted by the amplitude limiting amplifier 72.
And The I signal 67 and the Q signal 68 are the 90-degree phase shifter 62.
Therefore, a relative phase difference of 90 degrees is generated due to the frequency shift of the received wave, that is, depending on whether the received data is "0" or "1". Utilizing this relative phase difference, the logical operation circuit 74 to which the digital signals 70 and 73 are input is demodulated.

[0006]

However, when performing intermittent reception in the direct conversion receiver, there is a problem that the rise time is long and the power saving effect of intermittent communication is small. This will be explained below.

To achieve low power consumption, it is general to employ intermittent reception as communication. What is intermittent reception?
As shown in, the power of the receiving circuit is periodically turned on (1 cycle of T1 in the figure), and if a radio wave comes from the other party at this time, the power of the receiving circuit is continuously turned on to perform the demodulation operation ( (Section A in the figure), when there is no radio wave from the other party, the power is immediately turned off and the system waits until the next cycle to save power (section B in the figure). Therefore, in intermittent reception, the time from when the receiving device is turned on until it is possible to confirm that the receiving circuit is stable and that no radio waves are coming from the other party (T2 in the figure, hereafter The shorter the time (called time), the greater the power saving effect.

However, the conventional direct conversion receiving device has a problem that the rise time is long and the power saving effect is not great.

In order to operate the receiver in FIG. 9, the DC voltage levels of the output signals of the first mixing means 61 and the second mixing means 63 and the input of the data demodulation means (low pass filters 65, 66). Must be the same as the DC voltage level of. The output DC voltage level varies depending on the signal level of the antenna input 60, the ambient temperature, and the like. Alternatively, the DC voltage level immediately after the power of the receiving device is turned ON rises due to the time constant of each of the mixing means and the low pass filter, and the DC voltage level is not the same. Therefore, a DC removing means such as a capacitor is connected between the mixing means 61, 63 and the low-pass filters 63, 66. At this time, in the direct conversion receiving device, the capacitance of the capacitor is increased so that 1 k included in the signals output from the mixing means 61 and 63 is included.
Allow baseband signals below Hz to pass as low as possible. As a result, the time constant of the DC removing means becomes large and the rise time becomes long.

That is, there is a correlation between DC removal and rise time. For example, in a circuit using a capacitor as DC removal means, the product of the capacitance of the capacitor and the input resistance of the low pass filter is the low cutoff frequency, and during charging / discharging. Becomes the time constant of.

The present invention solves the above problems by shortening the rise time when the power is turned on in the direct conversion receiver.
The purpose is to increase the power saving effect in intermittent communication.

[0012]

In order to achieve the above object, the present invention comprises a signal generating means for outputting a signal having a frequency close to the carrier signal frequency of a received signal, and a signal from the signal generating means and a received signal. First mixing means for extracting a first signal having a difference frequency, first direct current removing means for removing a direct current component from the first signal by connecting to the first mixing means, and the signal generating means A second mixing means for extracting a second signal having a difference frequency from the signal obtained by phase-shifting the signal from the received signal, and a DC component from the second signal by connecting to the second mixing means. A second direct current removing means for removing the data, a data demodulating means for inputting a signal from the first direct current removing means and the second direct current removing means to perform data demodulation, and a predetermined timing. In comprising a constant switching means when switching the time constant of the first DC removal means and said second DC removal means.

In addition, there is provided time constant switching means for reducing the time constant of the first direct current removing means and the time constant of the second direct current removing means for a predetermined time when power is supplied to the receiving device.

Alternatively, there is provided time constant switching means for increasing the time constant of the first direct current removing means and the time constant of the second direct current removing means at the same time when the power supply to the receiving device is stopped. Further, there is provided time constant switching means for switching a first resistance value for determining the time constant of the first direct current removing means and a second resistance value for determining the time constant of the second time constant switching means by an electronic switch.

Further, there is provided time constant switching means for inverting the output signal of the DC removing means by the inverting means and feeding back to the output side of the DC removing means via an electronic switch.

Further, there is provided time constant switching means for changing the timing for switching the time constants of the first and second direct current removing means in response to a signal from a temperature sensor for detecting the ambient temperature.

Further, according to the signal from the voltage measuring unit for measuring the DC voltage of the first signal and the DC voltage of the second signal,
Time constant switching means for changing the timing for switching the time constants of the first and second DC removing means is provided.

[0018]

According to the above construction, since the time constant switching means switches the time constant of the DC removing means at a predetermined timing, the rise time can be shortened.

In addition, since the time constant of the direct current removing means is reduced for a predetermined time when power is supplied to the receiving device, charging becomes faster and rise time can be shortened.

Alternatively, since the time constant of the DC removing means is increased at the same time when the power supply to the receiving device is stopped, the discharge is delayed and the rise time can be shortened.

Further, since the resistance value for determining the time constant is switched by the electronic switch, the time constant switching means can be easily realized.

Then, since the inverting means feeds back the direct current removing means, the rise time can be shortened.

Further, it is possible to adjust the timing of switching the time constant by detecting the fluctuation of the DC voltage level from the mixing means due to the change of the ambient temperature by the temperature sensor.

Further, the timing of switching the time constant can be adjusted by detecting the fluctuation of the DC voltage level of the mixing means by the voltage measuring section.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 is an antenna for receiving a received signal, 2 is a local oscillator, which is a signal generating means for outputting a signal having a frequency substantially equal to the carrier frequency of the signal to be received, 3 is a first mixing means, and 4 is a second mixing means. Reference numeral 5 denotes a 90-degree phase shifter that shifts the phase of the signal from the signal generating means 2 by 90 degrees.
Is a data demodulation means for demodulating data from the phase difference between the output signals of the first mixing means 3 and the second mixing means 4, and includes a low pass filter and an amplifier. These form a direct conversion receiver. In addition, 6 is a first capacitor that is a DC voltage removing unit that removes a DC component from the output signal of the first mixing unit 3, and 7 is a DC voltage that removes a DC component from the output signal of the second mixing unit 4. A second capacitor as a removing means, 8 is a first time constant switching means for switching the time constant of the first capacitor 6, and 9 is a second time constant switching means for switching the time constant of the second capacitor 7. . The first mixing means 3 and the second mixing means 4 constitute a mixer IC 11, and 12 is a mixer IC.
11, a power supply unit for supplying power to the data demodulation unit 10, the first time constant switching unit 8 and the second time constant switching unit 9, and 13 connects / disconnects the power supply unit 12, the mixer IC 11 and the data demodulation unit 10. The power switch means 14 is a power control section for controlling the power switch means 13. Since the direct conversion receiving device uses a baseband signal of 1 kHz or less, the time constants of the first capacitor 6 and the second capacitor 7 become large, and the charging time thereof becomes a factor to prolong the rise time when the power is turned on. Therefore, when the power supply controller 14 connects the power supply switch means 13 and turns on the power supply, the first time constant switching means 8 and the second time constant switching means 9 operate to switch the time constants. As a method of switching the time constant, the time constant may be increased at the same time when the power is not supplied to the receiving device, or the time constant may be decreased for a predetermined time when the power is supplied to the receiving device. If the first time constant switching means 8 and the second time constant switching means 9 are electronic switches such as transistors, they can be housed in the IC together with the data demodulation section.

An example of increasing the time constant will be described with reference to FIG. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted. In FIG. 2, the time constant switching means is a switch for connecting / disconnecting the capacitor and the data demodulating means.
When the power supply control unit 14 controls the power supply switch unit 13 to supply power to the mixer IC 11 and the data demodulation unit 10, the first time constant switching unit 8 and the second time constant switching unit 9 are connected and operated. When not supplied, the first capacitor 6 and the second capacitor 7 are released from the data demodulation means 10 to increase the time constant. Once the charge is once discharged, it takes a long time to be discharged, and if power is supplied before that, the charge newly charged in the capacitor is small and the rise time becomes short.

An example of reducing the time constant will be described with reference to FIG. The same parts as those in FIG. 1 are designated by the same reference numerals, the description thereof will be omitted, and the points different from FIG. 1 will be mainly described. This embodiment differs from FIG. 1 in that a charging circuit 18 is provided in the capacitors 6 and 7 which constitute the direct current removing means.
The charging circuit 18 includes a first time constant switching means 8 for connecting / disconnecting the first capacitor 6 and the voltage source 17, and a second time constant switching for connecting / disconnecting the second capacitor 7 and the voltage source 17. It is composed of means 9. The output voltage of the voltage source 17 has the same potential as the terminal connecting the capacitors 6 and 7 and the data demodulating means 10. First capacitor 6 and data demodulation means 1
When the voltage connected to the terminal connected to 0 and the voltage connected to the terminal connecting the second capacitor 7 and the data demodulating means 10 are different, each may have its own voltage source. The charging circuit 18 connects a resistor in parallel with the input resistor of the data demodulating means 10 to reduce the time constant of charging, and the power switch means 13
It operates in synchronization with. When the power supply to the receiving device is started, the power supply control unit 14 sets the charging circuit 1 accordingly.
8 is operated for t time, and the time constant is switched by the time constant switching means 8 and 9 to reduce the time constant and charge faster, thereby increasing the rising time.

If the time t is too short, the rising time will not be shortened. Further, during the time t, the signals from the first mixing means 3 and the second mixing means 4 are not normally input to the data demodulation means 10 due to the operation of the charging circuit 18 and cannot be demodulated. Therefore, if the time t is too long, the rise time becomes long. By selecting the optimum t, the charging time of the first and second capacitors can be shortened and the rising time can be shortened. Here, when the output DC levels of the first mixing means 3 and the second mixing means 4 are different, the rise times are different even if the time constants are the same.
In such a case, the time t is set according to the longer rising time.

Another example of reducing the time constant will be described with reference to FIG. The same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof is omitted. The difference from FIG. 2 is the data demodulation means 1.
Negative feedback is applied from 0 to the capacitor, which is the DC removing means. This will be specifically described below. In FIG. 3, reference numeral 19 is a first inverting means for inputting the signal from the first capacitor 6 and inverting the positive / negative of the voltage and outputting the same, which is a part of a low-pass filter and an amplifier. This first reversing means 1
The output signal of 9 is fed back to the output side of the first capacitor 6 via the first time constant switching means 8. However, the DC voltage level of the signal passed through the first inverting means 19 is equal to the DC voltage level of the terminal connecting the first capacitor 6 and the data demodulating means 10. The first time constant switching means 8 is connected / opened in synchronization with the power switch means 13. Similarly for the second capacitor, the output signal of the second inverting means 20 is passed through the second time constant switching means 9 to the second capacitor 7
Return to the output side of.

When power is supplied to the receiving device, the power supply control unit 14 connects the first time constant switching means 8 and the second time constant switching means 9 for t time accordingly. Not only is the time constant of the DC removing means reduced, but negative feedback is applied, so the rise time is further shortened. For example, when the capacitor is not sufficiently charged and the input voltage of the inverting means is low, the output voltage of the inverting means becomes high and a current flows in the direction to charge the capacitor. Further, when the capacitor overshoots due to the transient response of charging and the input voltage of the inverting means becomes too high, the output voltage of the inverting means becomes low and a current flows in a direction to discharge the capacitor and lower the voltage.

If an amplifier is provided in the negative feedback, such a function is more remarkable because even a slight potential fluctuation is amplified and the feedback is applied. From the inverting means 19 constituting the low frequency amplifier as shown in FIG. Apply negative feedback. Alternatively, as shown in FIG. 6, a low-pass filter may be configured by the inverting means 19 and a non-inverted amplifier may be connected to this to provide negative feedback. Of course, another amplifier or filter may be inserted and connected to the portion shown by the broken line in the drawing such as between the capacitor 6 and the amplifier or filter. That is, by using the inverting means in the data demodulating means, no new inverting means is needed.

Although the operational amplifier is used as the inverting means here, the invention is not limited to this. It is sufficient that the output signal of the inverting means and the DC voltage level of the output side of the DC removing means are the same.

Further, the inverting means is used as an input buffer of the data demodulating means as shown in FIG. The input resistance of the data demodulating means can be increased by R1 and the capacity of the capacitor 6 can be reduced, which is advantageous in mounting. In particular, a large-capacity capacitor not only has a large mounting area, but also has large variations in capacity and changes in temperature, and the rise time changes with temperature.

The DC voltage levels of the output signals from the first and second mixing means vary depending on the signal level from the antenna input, the signal level from the signal generating means (local oscillator), the ambient temperature and the like. Therefore, as shown in FIG. 4, if the temperature sensor 21 is provided to detect the ambient temperature of the receiving device and the power supply control unit 14 changes the operating time t of the charging circuit depending on the temperature, the temperature of the mixing unit as well as the temperature of the capacitor is changed. It is possible to minimize the rise time including the characteristics. Alternatively, although not shown, a voltage measuring unit is provided to measure the DC voltage level of the output signals from the first mixing unit and the second mixing unit, and the power supply control unit determines the operating time t of the time constant switching unit to the DC voltage level. Take a configuration that changes depending on. As a result, the shortest output time can be obtained from the outputs from the two mixing means at that time.

In the above description, the direct current removing means has been described by inserting a capacitor in series between the mixing means and the data demodulating means, but the direct current removing means is not limited to this. Although not a reversing means, for example, the configuration shown in FIG. 8 may be used. When the power is supplied to operate the direct current removing means, the power supply is controlled by the power supply control unit to start / stop the supply simultaneously with the mixing means and the data demodulating means. As a result, it is possible to perform the intermittent operation including the DC removing means and further reduce the power consumption.

[0036]

As described above, according to the present invention, it is possible to shorten the rise time when the power is turned on and perform intermittent communication with a high power saving effect. Due to this effect, it can be driven for a long time with a battery power supply, and it is a rechargeable type such as a radio for a telemeter used for meter reading of gas, water, electricity meters, etc. The use of wireless devices is expanding even in fields where batteries cannot be used.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram of a receiver according to another embodiment of the present invention.

FIG. 3 is a block diagram of a receiving device according to another embodiment of the present invention.

FIG. 4 is a block diagram of a receiver according to another embodiment of the present invention.

FIG. 5 is a block diagram of a reversing means in an embodiment of the present invention.

FIG. 6 is a block diagram of a reversing means in another embodiment of the present invention.

FIG. 7 is a block diagram of inverting means in another embodiment of the present invention.

FIG. 8 is a block diagram of a DC removing means according to another embodiment of the present invention.

FIG. 9 is a block diagram of a conventional receiving device.

FIG. 10 is a timing chart of intermittent reception.

[Explanation of symbols]

1 antenna 2 Signal generation means 3, 4 mixing means 5 90 degree phase shifter 6, 7 capacitors 8, 9 Time constant switching means 10 Data demodulation means 11 Mixer IC 12 power supply 13 Power switch means 14 Power control unit 17 Voltage source 19, 20 Inversion means 21 Temperature sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-307343 (JP, A) JP-A-3-16349 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 27/00-27/38

Claims (8)

(57) [Claims] 1. A signal generating means for outputting a signal having a frequency close to a carrier signal frequency of a received signal, and a first signal for taking out a first signal having a difference frequency from the signal from said signal generating means and the received signal. Mixing means, a first direct current removing means connected to the first mixing means to remove a direct current component from the first signal, a signal obtained by phase-shifting the signal from the signal generating means, and the received signal. Second mixing means for extracting a second signal having a difference frequency, second DC removing means for removing a DC component from the second signal by connecting to the second mixing means, and the first Data demodulating means for inputting signals from the DC removing means and the second DC removing means to perform data demodulation, the first DC removing means and the second DC removing means at a predetermined timing. Receiver including a constant switching means when switching the time constant of the unit. 2. The time constant switching means is configured to reduce the time constant of the first direct current removing means and the time constant of the second direct current removing means for a predetermined time when power is supplied to the receiving device. Item 1. The receiving device according to item 1. 3. The time constant switching means is configured to increase the time constant of the first direct current removing means and the time constant of the second direct current removing means at the same time when power is not supplied to the receiving device. Receiver. 4. A time constant switching means is an electronic switch that sets a first resistance value that determines the time constant of the first direct current removing means and a second resistance value that determines the time constant of the second time constant switching means. Claim 1 or Claim 2 configured to switch by
Alternatively, the receiving device according to claim 3. 5. The time constant switching means reverses the output signal of the direct current removing means by the inverting means and feeds it back to the output side of the direct current removing means via an electronic switch. The receiving device according to claim 2 or claim 4. 6. The receiving apparatus according to claim 5, wherein the inverting means uses an operational amplifier which forms an amplifier, a filter, or a buffer in the data demodulating means. 7. The time constant switching means is configured to change the time for switching the time constants of the first and second direct current removing means in response to a signal from a temperature sensor for detecting the ambient temperature. The receiver according to item 1. 8. The time constant switching means sets the time constants of the first and second direct current removing means in response to signals from a voltage measuring section for measuring the direct current voltage of the first signal and the direct current voltage of the second signal. The receiving device according to any one of claims 1 to 6, wherein the switching time is changed.