JP2005311657A - Radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable radio receiver by turning a threshold voltage for accurately binarizing demodulated signals to an appropriate value. <P>SOLUTION: The radio receiver comprises: a local oscillation part 5 for generating a local oscillation frequency; a mixer part 6 for mixing received radio waves with the local oscillation frequency from the local oscillation part 5 and converting them into an intermediate frequency; a demodulator 8 for demodulating signals converted into an intermediate frequency band; a low-pass filter part 9 for extracting the DC component of the demodulated signals as the threshold voltage; a comparator 10 for performing the binary comparison of the demodulated signals and the threshold voltage; a frequency division part 11 for outputting non-modulated signals turned to the center frequency of the intermediate frequency band; a switching part 12 for switching the signals from the frequency division part 11 and the output of the mixer part 6; and a threshold voltage adjusting part 13 for preserving an output voltage from the demodulator 8 when the output from the frequency division part 11 is selected by the switching part 12 and setting it to the comparator 10 as a reference threshold voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless receiver capable of receiving a radio wave obtained by modulating a digital signal with FSK (Frequency Shift Keying).

  In recent years, various standards have been standardized for wireless networks, and devices having various applications have been connected to wireless networks of the same standard.

  For example, Bluetooth (Bluetooth (trademark)), which is a wireless network standard, can connect not only computers but also computer peripherals such as printers and scanners, facsimile devices, audio devices, cordless telephones, and the like according to the Bluetooth standard. it can.

  Bluetooth uses a frequency band from 2.402 GHz to 2.480 GHz called an ISM (Industry Science Medical) band, and FSK is used as the modulation method.

  The configuration of a conventional radio receiving apparatus will be described with reference to FIG. 6, taking as an example a single superheterodyne receiver that receives radio waves that are FSK modulated in the 2.4 GHz band, which is the ISM band. FIG. 6 is a diagram for explaining the configuration of a conventional radio receiving apparatus.

  As shown in FIG. 6, a conventional radio receiving apparatus 31 includes an antenna 32 for receiving radio waves, a bandpass filter unit 33, a high frequency amplifying unit 34, and local oscillation for down-conversion by PLL (Phase Locked Loop) control. A local oscillation unit 35 that outputs a frequency, a mixer unit 36, an IF (Intermediate Frequency) unit 37, a demodulator 38, a low-pass filter unit 39, a comparator 40, and a switch 41 are provided.

  The operation of the conventional radio receiving apparatus 31 configured as described above will be described.

  First, the radio wave received by the antenna 32 passes only the radio wave signal in the ISM band 2.4 GHz band including the desired signal of 2450 MHz by the band pass filter unit 33. Next, the radio wave received by the high frequency amplifier 34 is amplified and output to the mixer unit 36. The mixer unit 36 receives a signal having a local oscillation frequency of 2448 MHz from the local oscillation unit 35 and down-converts the signal output from the high frequency amplification unit 34 to an intermediate frequency having a center frequency of 2 MHz. The signal output from the mixer unit 36 is input to the IF unit 37. Only the signal of the desired channel is selected as the signal input to the IF unit 37, and the signal is amplified. The demodulator 38 demodulates the FSK and outputs a Vin signal that is a baseband signal. From the Vin signal output from the demodulator 38, a DC component is extracted by the low-pass filter unit 39, and the voltage of the DC component is input to the comparator 40 as the threshold voltage Vth. The output of the demodulator 38 is compared with the Vin signal by the comparator 40 based on the threshold voltage Vth. Then, the comparator 40 outputs the result of binary comparison in which the period during which the Vin signal is higher than the threshold voltage Vth is 1 and the period during which the Vin signal is lower is 0, as the Vout signal.

In this way, the low-pass filter unit 39 sets the threshold voltage Vth in order to convert the FSK-modulated radio wave into a digital signal. Note that when the low-pass filter unit 39 closes the switch 41 for a certain period of time at the head of the packet and sets the threshold voltage Vth, the switch 41 continues to open and hold the threshold voltage Vth during packet reception, and the comparator 40 Binary comparison is performed with the threshold voltage Vth. Then, the low-pass filter unit 39 again sets the threshold voltage Vth by closing the switch 41 for a predetermined time at the head of the next packet. The low-pass filter unit 39 repeats this operation.

  A method of extracting a DC component by the low-pass filter unit 39 and using this as a threshold value to binary-determine the baseband signal by the comparator 40 is constituted by a CR circuit which is called a data slicer and is an integration circuit of a capacitor and a resistor. Since it is inexpensive and simple, it is often used.

  An operation in which the low-pass filter unit 39 outputs the threshold voltage Vth will be described in detail with reference to FIG. FIG. 7 is a diagram for explaining the operation of the low-pass filter unit 39.

  As shown in FIG. 7, the RXENable signal indicates a period during which the conventional radio receiving apparatus 31 receives a high voltage portion. The Sample & Hold signal is a control signal to the switch 41 and is a period during which the high voltage portion closes the switch 41 and samples the threshold voltage Vth. Also, when the Sample & Hold signal changes from a high voltage to a low voltage, the switch 41 is opened to hold the threshold voltage Vth. The Vin signal is a baseband signal output from the demodulator 38. The output of the comparator 40 that binary-determines the Vin signal with the threshold voltage Vth is the Vout signal.

  In Bluetooth, 4-bit data, which repeats alternately 1 and 0 having a 1 μs width called a preamble, is transmitted at the beginning of a packet. This preamble is provided so that the threshold voltage Vth can be accurately set to a voltage near the median value of the Vin signal. This is because the preamble uses 4-bit data in which 1 and 0 are alternately repeated, so that the balance of charging and discharging of the capacitor and the resistor constituting the low-pass filter unit 39 can be maintained. The low-pass filter unit 39 uses the preamble period as the sample period for setting the above-described threshold voltage Vth, closes the switch 41 and sets the threshold voltage Vth, and then opens the switch 41 and holds this value for comparison. Accurate binary comparison by the device 40 becomes possible.

  However, when the distribution of 1 and 0 of the Vin signal that is output from the demodulator 38 is unbalanced during the sampling period, particularly when 1 continues continuously or when 0 continues continuously, the low-pass filter The difference in threshold voltage Vth, which is the output of the unit 39, differs from the original value.

  For example, when the noise interferes with the transmission packet, when the distance from the wireless transmission device is far and the electric field strength of the transmission packet is weak, or when no wireless transmission device is transmitting, the preamble cannot be received normally. Sometimes.

  FIG. 8 shows a state in which the preamble of the first communication period (slot) is not normal and there is no signal that can be received during the period that the low-pass filter unit 39 samples.

  In this case, the low-pass filter unit 39 holds the threshold voltage Vth while being extremely lowered. For this reason, the 4-bit preamble in the next communication period is too short, and the threshold voltage Vth cannot be increased to a voltage near the median value of the Vin signal.

Therefore, the threshold voltage Vth becomes low, and the comparator 40 cannot accurately perform binary comparison. When the time constant of the low-pass filter 39 is shortened, the time until Vth follows the input signal and reaches the original value follows the input signal in a short time. On the other hand, if the time constant of the low-pass filter 39 is shortened, the cut-off frequency is increased, and the signal component cannot be completely attenuated by the low-pass filter for extracting the DC component. Thus, it becomes a trade-off between the follow-up speed and the required attenuation amount of the signal component, and it is difficult to realize a low-pass filter that follows a large potential difference within a short preamble period.

  As described above, if the comparator 40 cannot accurately perform binary comparison, even a normally transmitted packet may be erroneously determined to be a communication error, leading to a decrease in communication reliability.

  Patent Document 1 discloses a digital signal forming circuit that can accurately extract a threshold voltage for converting such a demodulated signal into a digital signal by binary comparison.

The digital signal forming circuit described in Patent Document 1 detects a noise based on the amplitude width of a demodulated signal from a demodulator, and extracts a reference voltage for binary comparison in accordance with the noise (a reference voltage generation unit). Disconnect. Instead, the reference voltage from the additional voltage generator is used as a reference voltage for binary comparison of the signal comparator. As a result, the deviation of the reference level of the digital signal output from the signal comparator can be corrected.
JP-A-11-215086

  However, the digital signal forming circuit described in Patent Document 1 is based on a reference voltage from a reference voltage generation unit different from the signal output from the demodulator. On the other hand, the voltage of the DC component of the baseband signal (Vin signal) to be subjected to binary comparison may deviate from the design value due to demodulator variations.

  The deviation of the DC component voltage output from this demodulator is due to variations in the components that make up the demodulator, temperature changes due to the installation environment, or heat generation of the parts. To do.

  Therefore, even if the reference voltage is determined in advance in consideration of variations in the demodulator, the voltage of the DC component of the baseband signal (Vin signal) of the signal output from the demodulator changes depending on the usage environment.

  As described above, when the DC component of the baseband signal output from the demodulator is shifted in the + direction or the − direction, the threshold voltage used for the binary comparison is set to a voltage near the median value of the baseband signal. Therefore, an accurate binary comparison cannot be performed by the comparator.

  Accordingly, an object of the present invention is to provide a highly reliable radio receiving apparatus by setting an appropriate threshold voltage for binarizing a demodulated signal accurately.

  The present invention includes a local oscillation unit that generates a local oscillation frequency, a mixer unit that mixes a received radio wave with a local oscillation frequency from the local oscillation unit to convert it to an intermediate frequency, and a signal converted to the intermediate frequency. In the radio receiving apparatus, comprising: a demodulator that demodulates; a low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage; and a comparator that compares the demodulated signal and the threshold voltage in binary. An adjustment signal generating unit that outputs an unmodulated signal having a frequency equal to the intermediate frequency, a switching unit that switches an output of the adjustment signal generating unit and an output of the mixer unit, and the adjustment signal generating unit by the switching unit A threshold voltage adjustment unit that stores an output voltage from the demodulator when selected and temporarily sets the voltage as a reference threshold voltage in the comparator; Characterized in that was.

  The wireless receiver of the present invention includes a local oscillation unit that generates a local oscillation frequency, a mixer unit that mixes the received radio wave with the local oscillation frequency from the local oscillation unit and converts the mixed radio wave to an intermediate frequency, and the intermediate frequency converted to the intermediate frequency In a radio reception apparatus having a demodulator that demodulates a signal, a low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage, and a comparator that compares the demodulated signal and the threshold voltage in binary, an intermediate frequency When the adjustment signal generator is selected by the switching unit, the adjustment signal generator that outputs an unmodulated signal having the same frequency as the output, the switching unit that switches the output of the adjustment signal generator and the output of the mixer unit, A threshold voltage adjustment unit that stores the output voltage from the demodulator and temporarily sets the voltage as a reference threshold voltage in the comparator. Taking out a signal of only the DC component containing the variability can be stored. The threshold voltage adjustment unit temporarily sets this voltage as a reference threshold voltage to the comparator, so that the threshold voltage reaches the desired voltage following the input signal in a short time, so that the comparator accurately binary. You can compare. Therefore, since the threshold voltage for accurately binarizing the demodulated signal can be set to an appropriate value, a highly reliable wireless reception device can be obtained.

  1st invention of this application is a local oscillation part which generates a local oscillation frequency, a mixer part which mixes the received electric wave with a local oscillation frequency from a local oscillation part, and converts it into an intermediate frequency, and was converted into an intermediate frequency In a radio reception apparatus having a demodulator that demodulates a signal, a low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage, and a comparator that compares the demodulated signal and the threshold voltage in binary, an intermediate frequency An adjustment signal generating unit that outputs an unmodulated signal having a frequency equal to the frequency, a switching unit that switches the output of the adjustment signal generating unit and the output of the mixer unit, and demodulation when the adjustment signal generating unit is selected by the switching unit And a threshold voltage adjusting unit that stores the output voltage from the comparator and temporarily sets the voltage as a reference threshold voltage in the comparator.

  By switching a non-modulated signal having a frequency equal to the intermediate frequency output from the adjustment signal generator to the demodulator by switching the switching unit, a signal having only a DC component is output from the demodulator. That is, since this signal is demodulated by a demodulator of an unmodulated signal having a frequency equal to the intermediate frequency, it becomes a DC voltage including a deviation from the design value due to variations in the demodulator. The threshold voltage adjustment unit stores this voltage and temporarily sets it as a reference threshold voltage to the comparator, so that the threshold voltage reaches the desired voltage following the input signal in a short time. It is possible to compare two values.

  The second invention of the present application is a local oscillation unit that generates a local oscillation frequency, a mixer unit that mixes a received radio wave with a local oscillation frequency from the local oscillation unit and converts it to an intermediate frequency, and an intermediate frequency converted In a radio reception apparatus having a demodulator that demodulates a signal, a low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage, and a comparator that compares the demodulated signal and the threshold voltage in binary, an intermediate frequency A signal generator for adjustment that outputs a non-modulated signal having a frequency equal to that, a switching unit that switches the signal from the adjustment oscillator and the output of the mixer unit, a reference for the demodulator output, and temporarily as a reference threshold voltage When a power supply unit that generates a voltage to be set in the comparator and an adjustment signal generation unit are selected by the switching unit, an output signal from the demodulator and a reference from the power supply unit A demodulating voltage adjusting unit that compares the voltages and feeds back the comparison result to the demodulator, and the demodulator calibrates the voltage of the DC component of the signal demodulated by the demodulating voltage adjusting unit. is there.

By switching a non-modulated signal having a frequency equal to the intermediate frequency output from the adjustment signal generator to the demodulator by switching the switching unit, a signal having only a DC component is output from the demodulator. That is, since this signal is a demodulator demodulating an unmodulated signal having a frequency equal to the intermediate frequency, it becomes a DC voltage including variations of the demodulator. The threshold voltage adjustment unit compares this voltage with the reference voltage from the power supply unit, and feeds back the comparison result to the demodulator. Then, by calibrating so that the demodulator output voltage is equal to the reference voltage, it is possible to adjust the variation in the output voltage of the demodulator when the unmodulated signal is demodulated. Furthermore, by setting the same reference voltage as the reference threshold voltage temporarily in the comparator during communication, the threshold voltage reaches the desired voltage following the input signal in a short time. It is possible to compare two values.

  The third invention of the present application is characterized in that the adjustment signal generator is a frequency divider that divides and outputs a signal from the local oscillator.

  By configuring the adjustment signal generator with a frequency divider that divides and outputs the signal from the local oscillator, there is no need to provide an oscillator that oscillates an unmodulated signal having the same frequency as the intermediate frequency. The scale can be small.

(Embodiment 1)
Hereinafter, a radio reception communication apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings, taking as an example a single superheterodyne receiver that receives radio waves modulated in the 2.4 GHz band which is an ISM band. FIG. 1 is a diagram for explaining a configuration of a radio reception apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 1, a radio receiving apparatus 1 includes an antenna 2 that receives radio waves, a bandpass filter unit 3, a high-frequency amplification unit 4, a local oscillation unit 5 that generates a local oscillation frequency by PLL control, and a mixer. A unit 6, an IF unit 7, a demodulator 8, a low-pass filter unit 9, and a comparator 10 are provided.

  Further, the wireless reception device 1 includes a frequency division unit 11, a switching unit 12, a threshold voltage adjustment unit 13, and switches 14 and 15.

  The band-pass filter unit 3 passes only signals that have received the ISM band 2.4 GHz band including the desired signal of 2450 MHz.

  The high frequency amplifier 4 amplifies the received high frequency signal in the 2.4 GHz band.

  The local oscillator 5 generates a local oscillation frequency of 2448 MHz in order to convert a desired high frequency signal of 2450 MHz into an intermediate frequency of 2 MHz.

  The mixer unit 6 mixes with a desired signal of 2450 MHz to down-convert the output signal from the high-frequency amplifier unit 4 to an intermediate frequency of 2 MHz.

  The IF unit 7 selects only a signal of a desired channel from the input signal, and amplifies the signal.

  The demodulator 8 demodulates the FSK and outputs a Vin signal that is a baseband signal.

  The low-pass filter unit 9 extracts a DC component from the Vin signal output from the demodulator 8 while the switch 14 is closed. The extracted DC component voltage is input to the comparator 10 as the threshold voltage Vth. In the first embodiment, the low-pass filter unit 9 is configured by a CR circuit using a capacitor and a resistor. However, as long as the DC component of the Vin signal output from the demodulator 8 can be extracted, any method can be used. A simple circuit configuration may be adopted. While the switch 14 is open, the extracted threshold voltage Vth, which is a direct current component, is maintained.

The comparator 10 compares the Vin signal output from the demodulator 8 with a threshold voltage Vth to convert it to a binary value, and converts the FSK demodulated signal into a digital signal. That is, the comparator 10 outputs, as a Vout signal, a binary comparison result in which the period during which the Vin signal is higher than the threshold voltage Vth is 1 and the period during which the Vin signal is lower is 0.

  The frequency divider 11 is an adjustment signal generator that divides the frequency of 2448 MHz output from the local oscillator 5 by 1224 and outputs an unmodulated signal of 2 MHz.

  The switching unit 12 is a switch that switches the output from the mixer unit 6 and the output from the frequency dividing unit 11. The switching of the switching unit 12 is controlled together with the threshold voltage adjusting unit 13 by a control line (not shown).

  The threshold voltage adjusting unit 13 has a function of storing the output voltage from the demodulator 8 when the output from the frequency dividing unit 11 is selected by the switching unit 12 and setting the reference voltage 10 as the reference threshold voltage Vth.

  The switch 14 connects the demodulator 8 and the threshold voltage adjustment unit 13 to the low-pass filter unit 9. The switch 15 connects the threshold voltage adjusting unit 13, the low-pass filter unit 9, and the comparator 10. The connection state of these switches 14 and 15 is controlled together with the threshold voltage adjusting unit 13 by a control line (not shown).

  The operation of the radio reception apparatus according to Embodiment 1 of the present invention configured as described above will be described with reference to the drawings.

  The wireless reception device 1 performs a calibration operation for storing the reference threshold voltage and a normal operation for operating the data slicer with the reference threshold voltage as an initial value.

  First, the operation of the wireless reception device 1 during the calibration operation for storing the reference threshold voltage will be described.

  When the reference threshold voltage is set, the connection of the switching unit 12 is controlled to connect the output from the frequency dividing unit 11 to the IF unit 7. The switch 14 is open and the switch 15 is open.

  The frequency divider 11 receives a 2448 MHz signal from the local oscillator 5, divides the frequency by 1224, and outputs a 2 MHz unmodulated signal equal to the intermediate frequency.

  This unmodulated signal is input to the IF unit 7 because the switching unit 12 connects the output of the frequency dividing unit 11 and the input of the IF unit 7.

  The unmodulated signal is amplified via the IF unit 7 and input to the demodulator 8.

  The demodulator 8 demodulates the unmodulated signal output from the IF unit 7. This signal is a signal of only a direct current component because a non-modulated signal having a frequency equal to the intermediate frequency is demodulated by the demodulator, and is a direct current voltage including variations of the demodulator 8.

  The threshold voltage adjustment unit 13 holds this DC voltage as a reference threshold voltage.

  Next, the operation of the wireless reception device 1 during the normal operation will be described based on FIG. 1 and FIG. FIG. 2 is a diagram for explaining the timing at which the radio reception apparatus according to Embodiment 1 of the present invention sets the threshold voltage. In FIG. 1, the switching unit 12 always keeps the output of the mixer unit 6 connected to the IF unit 7 during normal operation.

  As illustrated in FIG. 2, the RXENable signal indicates a period during which the wireless reception device 1 receives a high voltage portion. The Slicer Reset signal is a control signal for the switch 15 and is a period in which the high voltage portion closes the switch 15 and applies the reference threshold voltage to the threshold voltage Vth. The Sample & Hold signal is a control signal for the switch 14 and is a period during which the high voltage portion closes the switch 14 and samples the threshold voltage Vth. The low-pass filter unit 9 holds the threshold voltage Vth when the Sample & Hold signal changes from a high voltage to a low voltage. The Vin signal is a baseband signal output from the demodulator 8. The output of the comparator 10 that binary-determines the Vin signal with the threshold voltage Vth is the Vout signal.

  The first communication period represents a state in which there is no packet transmitted from any wireless transmission device and ambient noise is received. In such a reception state, the voltage of the DC component of the baseband signal output from the demodulator is extremely shifted in the-(minus) direction. Even after the end of the communication period, the switch 14 remains open and the threshold voltage Vth is maintained in a deviated state.

  Therefore, when the switch 15 is closed while the switch 14 is open at the timing T immediately before the preamble, the reference threshold voltage held by the threshold voltage adjusting unit 13 is applied to the threshold voltage Vth. In the present embodiment, since the low-pass filter unit 9 is a CR circuit, the capacitor of the output stage of the low-pass filter unit 9 is charged by short-circuiting the output of the threshold voltage adjusting unit 13 and the output of the low-pass filter unit 9. Therefore, the threshold voltage Vth that has shifted extremely in the minus (minus) direction with respect to the desired voltage is forcibly equal to the reference threshold voltage (reset).

  Next, at the beginning of the preamble period, the switch 14 is closed and the switch 15 is opened. The reference threshold voltage applied from the threshold voltage adjusting unit 13 is disconnected from the threshold voltage Vth, while the output signal of the demodulator 8 is input to the low-pass filter 9, so that the threshold voltage Vth has the reference threshold voltage as an initial value. Thus, it follows the DC component of the demodulated preamble as in the conventional technique. Since the reference threshold voltage is a voltage obtained by demodulating an unmodulated signal having a frequency equal to the intermediate frequency with the demodulator 8, it is a voltage close to the direct current component of the actual input signal. The threshold voltage Vth can reach an appropriate voltage even within a short preamble period.

  When the preamble period ends, switch 15 remains open and switch 14 is opened. The input of the low-pass filter 9 is cut off, and the threshold voltage Vth is held by the low-pass filter 9. The threshold voltage Vth at this time has reached an appropriate voltage following the input signal during the preamble period regardless of the state in the previous communication period, so that the comparator 10 can accurately perform binary comparison.

The operation of forcibly resetting the threshold voltage Vth shown in FIG. 2 to the reference threshold voltage may be performed every communication period (slot) or every predetermined period. Moreover, you may perform according to a communication condition. When the wireless reception device 1 is used for Bluetooth communication, the threshold voltage Vth may be set after the wireless reception device 1 performs scanning. In addition, the calibration operation for storing the reference threshold voltage may be performed only once when the power is turned on, or may be performed every long cycle that can follow the ambient temperature. The threshold voltage adjustment unit 13 does not need to be expensive because the threshold voltage adjustment unit 13 does not need to be operated at high speed. Since the calibration operation is performed during a period other than during communication, the local oscillation frequency when generating the adjustment signal equal to the intermediate frequency may be set not to be used for communication. Although it must be designed to be able to generate a frequency exactly equal to the intermediate frequency in combination with the frequency divider 11, there is a degree of freedom in that it can be performed separately from the setting during communication.

  Next, the configuration of the threshold voltage adjusting unit 13 will be described in detail with reference to FIG. FIG. 3A and FIG. 3B are diagrams illustrating the configuration of the threshold voltage adjustment unit 13.

  As described above, the threshold voltage adjustment unit 13 connects the switching unit 12 and the output from the frequency dividing unit 11 to the input of the IF unit 7 during the calibration operation for storing the reference threshold voltage. It only needs to have a function of sampling and holding the voltage of the Vin signal output from the demodulator 8 as a reference threshold voltage.

  That is, as shown in FIG. 3A, the output from the demodulator 8 is input to the AD converter 13a to be converted and held into a digital signal, and the digital signal is converted to an analog signal by the DA converter 13b. Then, it may be outputted as a reference threshold voltage.

  Further, as shown in FIG. 3B, the comparator 13c compares the output of the DA converter 13e with the output from the demodulator 8, and both are equal (closest) by the control unit 13d. It is also possible to control so that the setting of the control unit 13d at that time is held, and the output of the DA converter 13e is used as the reference threshold voltage.

(Embodiment 2)
Next, a radio reception apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a radio reception apparatus according to Embodiment 2 of the present invention.

  The radio reception apparatus according to Embodiment 2 of the present invention is a reference for demodulator output, and also includes a power supply unit that generates a voltage temporarily set in the comparator as a reference threshold voltage, an output signal from the demodulator, and a power supply And a demodulated voltage adjusting unit that compares reference voltages from the units and feeds back the comparison results to the demodulator.

  In radio receiving apparatus 20 according to Embodiment 2 shown in FIG. 4, antenna 2, bandpass filter unit 3, high frequency amplification unit 4, local oscillation unit 5, mixer unit 6, and IF unit 7 The low-pass filter unit 9, the comparator 10, the frequency dividing unit 11, and the switching unit 12 are the same as those in FIG.

  As shown in FIG. 4, the wireless reception device 20 according to the second embodiment of the present invention is a power supply unit 21 that generates a voltage that is used as a reference for the demodulator 23 and temporarily set in the comparator 10 as a reference threshold voltage. It has.

  For example, if the design value of the output voltage of the demodulator 23 (that is, the center voltage of the demodulator) with respect to the input signal having the center frequency assumed by the wireless receiver 20 is 1.2 V, the power supply unit 21 is the same as this design value. It is a power supply that can output 1.2V.

  When the output from the frequency divider 11 is selected by the switching unit 12, the Vin signal that is an output signal from the demodulator 23 and the reference voltage from the power source unit 21 are compared, and the comparison result is sent to the demodulator 23. A demodulated voltage adjusting unit 22 for feedback is provided.

  The demodulator 23 has a function of calibrating the DC offset of the output voltage with the recovery adjustment voltage.

The configuration of the demodulated voltage adjustment unit 22 will be described in detail with reference to FIG. FIG. 5 shows a demodulated voltage adjustment unit 2
It is a figure explaining the structure of 2. FIG.

  As shown in FIG. 5, the demodulated voltage adjustment unit 22 includes a comparator 22a, a control unit 22b, and a DA converter 22c that supplies an adjustment voltage to the demodulator.

  The comparator 22 a compares the output voltage of the power supply unit 21 with the output voltage of the demodulator 23. Based on the comparison result, the control unit 22b controls the adjustment voltage output from the DA converter 22c so that the reference voltage from the power supply unit 21 and the output voltage of the demodulator 23 are equal (closest). To do.

  The operation of the radio receiving apparatus according to the second embodiment of the present invention configured as described above will be described with reference to FIGS.

  First, the operation of the wireless reception device 20 when calibrating the output voltage of the demodulator 23 will be described.

  When the demodulator 23 is calibrated, the connection of the switching unit 12 is in a state where the output from the frequency dividing unit 11 is connected to the IF unit 7. Further, the switch 14 and the switch 15 are opened.

  The frequency divider 11 receives a 2448 MHz signal from the local oscillator 5 and divides the frequency by 1224 to output a 2 MHz unmodulated signal equal to the intermediate frequency.

  This unmodulated signal is input to the IF unit 7 because the switching unit 12 connects the output of the frequency dividing unit 11 and the input of the IF unit 7.

  The unmodulated signal is amplified via the IF unit 7 and input to the demodulator 23.

  The demodulator 23 demodulates the non-modulated signal output from the IF unit 7. Since this signal is a demodulator 23 demodulating a non-modulated signal having a frequency equal to the intermediate frequency, it is a signal having only a DC component and a DC voltage including variations of the demodulator 23.

  As shown in FIG. 5, the output of the demodulator 23 is input to the comparator 22 a of the demodulated voltage adjustment unit 22. A reference voltage is input from the power supply unit 21 to the other input of the comparator 22a. For example, a voltage of 1.2 V is input from the power supply unit 21. The output voltage of the demodulator 23 and the reference voltage 1.2V of the power supply unit 21 are compared by the comparator 22a, and output from the DA converter 22c by the control unit 22b so that they are equal (closest). To control the adjustment voltage.

  Further, since the operation during the normal operation is the same as that of the first embodiment, it will be described with reference to FIG. As described in the first embodiment, in the first communication period, there is no packet transmitted from any wireless transmission device, and the threshold voltage Vth is held while being extremely shifted in the − (minus) direction. Yes.

  Therefore, when the switch 15 is closed while the switch 14 is open at the timing T immediately before the preamble, the reference threshold voltage 1.2V is applied from the power supply unit 21 to the threshold voltage Vth, and the threshold voltage Vth is forcibly set to the reference threshold. The voltage is equal to 1.2V.

Next, at the beginning of the preamble period, the switch 14 is closed and the switch 15 is opened. Since the reference threshold voltage 1.2V from the power supply unit 21 is disconnected from the threshold voltage Vth, while the output signal of the demodulator 23 is input to the low-pass filter 9, the threshold voltage Vth is the initial value of the reference threshold voltage 1.2V. As a result, it follows the DC component of the demodulated preamble. Here, since the demodulator 23 is calibrated so that its center voltage is equal to the reference voltage 1.2V, the DC component of the actually input preamble is also a voltage close to the reference voltage 1.2V. By setting the reference voltage 1.2V as an initial value of the threshold voltage Vth as a reference threshold voltage, Vth can reach an appropriate voltage even within a short preamble period.

  When the preamble period ends, the switch 15 remains open and the switch 14 is opened. The threshold voltage Vth is held by the low pass filter 9. The threshold voltage Vth at this time has reached an appropriate voltage following the input signal during the preamble period regardless of the state in the previous communication period, so that the comparator 10 can accurately perform binary comparison.

  Similar to the first embodiment, the operation of forcibly resetting the threshold voltage Vth shown in FIG. 2 to the reference threshold voltage may be performed every communication period (slot) or every predetermined period. Moreover, you may perform according to a communication condition. When the wireless reception device 1 is used for Bluetooth communication, the threshold voltage Vth may be set after the wireless reception device 1 performs scanning. Further, the operation of calibrating the demodulator may be performed only once when the power is turned on, or may be performed every long cycle that can follow the ambient temperature. It only needs to be executed when the system load due to communication is light, and it is not necessary to operate the demodulated voltage adjusting unit 22 at high speed, so that the components constituting the demodulated voltage adjusting unit 22 need not be expensive. Since the calibration operation is performed during a period other than during communication, the local oscillation frequency when generating the adjustment signal equal to the intermediate frequency may be set not to be used for communication. The design must be able to generate a frequency exactly equal to the intermediate frequency in combination with the frequency divider, but there is a degree of freedom in that it can be set separately from the setting during communication.

  Since the present invention can accurately perform binary comparison, the present invention is suitable for a radio reception apparatus that receives a radio wave in which a digital signal is FSK modulated.

The figure explaining the structure of the radio | wireless receiver which concerns on Embodiment 1 of this invention. The figure explaining the timing which the radio | wireless receiver which concerns on Embodiment 1 of this invention sets a threshold voltage The figure explaining the structure of a threshold voltage adjustment part The figure explaining the structure of the radio | wireless receiver which concerns on Embodiment 2 of this invention. The figure explaining the structure of a demodulation voltage adjustment part The figure explaining the structure of the conventional radio | wireless receiver. The figure explaining operation of a low pass filter part The figure which shows the communication state where preamble is not normal

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Wireless receiver 2 Antenna 3 Band pass filter 4 High frequency amplifier 5 Local oscillation part 6 Mixer part 7 IF part 8,23 Demodulator 9 Low pass filter part 10 Comparator 11 Dividing part 12 Switching part 13 Threshold voltage adjustment part 13a AD converter 13b DA converter 13c Comparator 13d Control unit 13e DA converter 21 Power supply unit 22 Demodulated voltage adjustment unit

Claims (3)

A local oscillator for generating a local oscillation frequency;
A mixer unit that mixes a received radio wave with a local oscillation frequency from the local oscillation unit and converts it to an intermediate frequency;
A demodulator that demodulates the signal converted to the intermediate frequency;
A low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage;
In a wireless reception device having the demodulated signal and a comparator for binary comparison of the threshold voltage,
An adjustment signal generator for outputting an unmodulated signal having a frequency equal to the intermediate frequency;
A switching unit for switching the output of the adjustment signal generating unit and the output of the mixer unit;
A threshold voltage adjustment unit that stores an output voltage from the demodulator when the adjustment signal generation unit is selected by the switching unit and temporarily sets the voltage as a reference threshold voltage in the comparator; A wireless receiver characterized by the above. A local oscillator for generating a local oscillation frequency;
A mixer unit that mixes a received radio wave with a local oscillation frequency from the local oscillation unit and converts it to an intermediate frequency;
A demodulator that demodulates the signal converted to the intermediate frequency;
A low-pass filter that extracts a DC component of the demodulated signal as a threshold voltage;
In a wireless reception device having the demodulated signal and a comparator for binary comparison of the threshold voltage,
An adjustment signal generator for outputting an unmodulated signal having a frequency equal to the intermediate frequency;
A switching unit that switches a signal from the adjustment oscillation unit and an output of the mixer unit;
A power supply unit that serves as a reference for the output of the demodulator and that temporarily generates a voltage to be set in the comparator as a reference threshold voltage;
A demodulating voltage adjusting unit that compares an output signal from the demodulator and a reference voltage from the power supply unit and feeds back the comparison result to the demodulator when the adjustment signal generating unit is selected by the switching unit; With
The radio receiver according to claim 1, wherein the demodulator calibrates a voltage of a DC component of the signal demodulated by the demodulated voltage adjustment unit. 3. The radio receiving apparatus according to claim 1, wherein the adjustment signal generating unit is a frequency dividing circuit that divides and outputs a signal from the local oscillating unit.

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