JP3266840B2 - Carrier detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier detection technique, and more particularly to a system for monitoring presence or absence of a desired reception signal frequency by applying a PLL circuit.

[0002]

2. Description of the Related Art In a specific low-power radio equipment, before transmitting a radio wave, it is checked whether or not a carrier having the same frequency as a carrier of the radio wave to be emitted exists in order to avoid collision of the radio wave. (Hereinafter referred to as carrier detection)
After that, a communication method of emitting radio waves is adopted.
The communication system that emits radio waves after carrier detection is widely used as a means for avoiding collision of radio waves and effectively using radio waves. By the way, in the case of using radio waves in a certain frequency range, it is required to add a carrier detection function to radio equipment by the Radio Law. Conventional carrier detection mainly has the following two types. (1) Signal level detection method (2) Noise level detection method

In the carrier detection method (1), first, the signal level is replaced with a DC voltage, and then a DC voltage is compared with a preset comparison voltage. Based on the comparison result, it is determined whether or not a desired radio wave exists. Is determined. FIG. 2 is a block diagram of a carrier detection device according to this method and a part of circuits constituting a receiver of a radio equipment. On the other hand, in the carrier detection method (2), first, a noise level of a signal is detected by any of a high-frequency circuit, an IF circuit, and a detection circuit constituting a receiver of a radio equipment, and the noise level is replaced with a DC voltage. Next, the DC voltage is compared with a preset comparison voltage, and it is determined whether or not a desired radio wave is present based on the comparison result. FIG. 3 is a block diagram of a part of circuits constituting the carrier detector and the receiver according to this method. In these figures, 1
Is a high frequency filter, 2 is a high frequency amplifier, 3 is a first frequency mixer, 4 is a first intermediate frequency filter, 5 is a second frequency mixer, 6 is a second intermediate frequency filter, 7 is an intermediate frequency amplifier, and 8 is a detection circuit. Is shown. In each system, the presence or absence of a carrier is determined based on a comparison result between a DC voltage converted from a signal and a preset comparison voltage.

[0004]

The carrier detecting device D2 adopting the method (1) shown in the block diagram of FIG. 2 includes a detecting circuit 17 and a comparing circuit 18. Here, the selection of the received signal is performed by the high-frequency filter 1 and the first and second intermediate frequency filters 4 and 6 that constitute the receiver. For example, when detecting a carrier at a certain frequency, a mixed wave near the intermediate frequency is generated between local oscillation frequencies due to a signal of an adjacent channel or an interfering wave having a close frequency. When the level of the mixed wave is high, the mixed wave passes through each filter together with the received signal corresponding to the intermediate frequency filter characteristic, and the level may exceed the level set by carrier detection. Then, the carrier detection device D2 shown in FIG. 2 malfunctions.

[0005] The carrier detection device D3 employing the method (2) shown in the block diagram of FIG. 3 includes a noise filter 19, an amplification circuit 20, a detection circuit 21, and a comparison circuit 22. Here, in the case of detecting a carrier at a certain frequency, when an adjacent interference wave is received, the reception wave and the interference wave within the reception band of the filter pass through the high frequency filter 1 of FIG. The received wave and the interfering wave that have passed through enter the high-frequency amplifier 2, and the received wave causes a noise suppression phenomenon due to an adjacent wave or an interfering wave in the nonlinear amplification region of the high-frequency amplifier 2. Due to this noise suppression phenomenon, the noise level rises relatively and exceeds the carrier detection level set for the desired reception wave. Then, the carrier detection device D shown in FIG.
No. 2 causes a malfunction. When line noise enters the receiver, the noise increases. When the noise is in the frequency band passing through the noise filter 19, the carrier detection device D2 shown in FIG. Would.

In order to prevent such a malfunction of the carrier detection device, it has conventionally been necessary to use a high-selectivity filter for the high-frequency filter 1 and the intermediate-frequency filters 4 and 6 provided in the receiver. In particular, in the carrier detection method (2), it is necessary to use amplifiers 2 and 7 having good dynamic ranges. However, such measures for preventing malfunction require high-performance and expensive circuits constituting the receiver for the carrier detection device, and have the disadvantage of increasing the cost of the entire receiver. Accordingly, it is an object of the present invention to provide a carrier detection device that is less likely to malfunction even when a high-level interference wave is received, and that can suppress an increase in the cost of a receiver.

[0007]

According to the present invention, there is provided a carrier detecting apparatus comprising: a frequency mixer for generating an intermediate frequency signal from a received high-frequency signal; a PLL unit having a phase comparator function and a frequency lock detecting function; A voltage-controlled oscillator that changes the frequency in accordance with the phase difference signal generated in the step, sets the intermediate frequency of the receiver as the lock frequency of the PLL unit, and the frequency of the received signal is in phase with the frequency set in the PLL unit. The frequency control of the voltage controlled oscillator is performed so that the lock signal when the PLL unit is locked is used as the carrier detection signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A second frequency mixer, a second intermediate frequency filter, an intermediate frequency amplifier, a PLL section, a loop filter, and a voltage controlled oscillator are arranged in a loop to form a PLL circuit. The PLL section has a frequency lock detection function in addition to the phase comparison function. When a radio wave exists in the frequency band to be transmitted / received, a first intermediate frequency signal that can pass through the first intermediate frequency filter is generated in the first frequency mixer. This first intermediate frequency signal is subjected to frequency conversion of the signal in a second frequency mixer,
It becomes the second intermediate frequency signal. The second intermediate frequency signal is controlled so that its frequency becomes the same as a reference intermediate frequency predetermined by the PLL circuit. When the frequency of the second intermediate frequency signal is locked to the reference intermediate frequency, a lock signal is output from the PLL unit. The output lock signal indicates the presence of a continuously existing radio signal, and has the meaning of carrier detection.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, malfunctions are less likely to occur even when an adjacent interference wave other than the desired frequency is received, and it is possible to suppress an increase in the cost of the receiver. An embodiment of the carrier detection device according to the present invention
It is shown in FIG. 1 together with some circuits constituting the receiver. FIG.
, A high frequency filter 1, a high frequency amplifier 2, a first frequency mixer 3, a first intermediate frequency filter 4, a second frequency mixer 5, a second intermediate frequency filter 6, an intermediate frequency amplifier 7, and a detection circuit 8 Is configured.
The carrier detection device D1 of the present invention applies the PLL unit 1 to the second frequency mixer 5, the second intermediate frequency filter 6, and the intermediate frequency amplifier 7 so as to form a loop with them.
6, the loop filter 13 and the voltage controlled oscillator 14 are arranged and configured.

Here, it is assumed that the PLL section 16 includes a divider 9, a reference oscillator 10, a phase comparator 11, and a frequency lock detector 12 as constituent elements. In addition,
As the reference oscillator 10 of the PLL section 16, an oscillator which receives a signal from a crystal oscillator 15 provided outside and generates a frequency signal with high stability is suitable. At present, the PLL unit 16 having such a configuration is integrated into an IC.
You can use it because it is inexpensive and widely available on the market. However, the present invention is not limited to this method. The operation of the carrier detection device D1 having such a configuration is as follows.

First, when there is a radio signal in a set frequency band, the high frequency filter 1 passes the radio signal. The radio signal (reception signal) that has passed through the high-frequency filter 1 is mixed with a first local oscillation frequency signal (1st Local) in a first frequency mixer 3. As a result, the received signal is frequency-converted into a first intermediate frequency signal (hereinafter, referred to as a first IF signal). This first IF signal is supplied to the carrier detection device D1 via the first intermediate frequency filter 4. In the carrier detection device D1, the first
The IF signal is further frequency-converted by the second frequency mixer 5 to become a second intermediate frequency signal (hereinafter, referred to as a second IF signal). While passing through the second intermediate frequency filter 6 and the intermediate frequency amplifier 7, the second IF signal extracts and amplifies a frequency signal required for carrier detection, and is input to the PLL unit 16.

Inside the PLL section 16, first, the signal frequency of the second IF signal is divided by the divider 9,
The comparison signal frequency f _D. On the other hand, the reference oscillator 10 generates a predetermined comparison signal frequency signal _fref . Comparison signal frequency signal f _ref and the comparison signal frequency f _D is input to the phase comparator 11. The phase comparator 11 compares the phases of the two, and generates a phase difference signal corresponding to the amount of phase displacement. This phase difference signal becomes a frequency control signal Vt in the loop filter 13 and is input to the voltage control oscillator 14. The voltage controlled oscillator 14 controls the frequency of a second local oscillation frequency signal (2nd Local) supplied to the second frequency mixer 5 according to the frequency control signal Vt. Frequency control signal Vt of the voltage controlled oscillator 10 so that the basic operation of the PLL the phase difference between the signals of the two comparison signal frequency f _D and f _ref is eliminated is controlled.

When the frequency of the second IF signal becomes substantially equal to the specified intermediate frequency and the frequency value is locked by the PLL section 13, the frequency lock detector 12 outputs a lock signal. This lock signal becomes a carrier detection signal indicating the presence of the received signal. In order to specify the range of the carrier frequency of the received signal by the receiver as shown in FIG. 1, the pass frequency band is fixed at the first local oscillation frequency, and at the same time, the frequency control range of the voltage controlled oscillator 14 as the second local oscillator is set. Must be narrowed. Specifically, the frequency control range of the voltage control transmitter 14 restricts the range of the control voltage of the frequency control signal Vt, and a condition that the PLL circuit is not locked when the received frequency exceeds a specific range. Make the settings for When the frequency is set to a specific frequency range as described above, the voltage control oscillator 14 may vary depending on conditions such as what kind of signal exists in an adjacent channel and how much frequency transition of the received signal occurs at the time of reception. In practice, it is desirable to set the frequency control range to an allowable range of the frequency of the received signal.

By controlling the frequency control range of the voltage controlled oscillator 14 in this way, even if a harmful signal exists in a channel adjacent to the channel of the original received signal, the PLL unit 16 can control the adjacent signal with respect to the adjacent signal. Therefore, a situation in which an adjacent signal is erroneously recognized as an original received signal can be prevented. In the carrier detection device according to the present invention described above, the second frequency mixer 5, the second intermediate frequency filter 6, and the intermediate frequency amplifier 7, which constitute the intermediate frequency circuit portion of the receiver, may be part of the carrier detection device D1. I'm using

[0015]

The carrier detection apparatus according to the present invention comprises a frequency mixer, an intermediate frequency filter, an intermediate frequency amplifier, and a PLL.
, A loop filter, and a voltage controlled oscillator are arranged in a loop to form a PLL circuit device. Where PLL
The unit having a phase comparison function and a frequency lock detection function is used. By determining the frequency control range of the voltage-controlled oscillator, it becomes possible to limit the frequency range of the desired received wave. Also, PLL
The lock signal output from the section is a carrier detection signal.

The carrier detecting apparatus of the present invention having such a configuration can share components with a general PLL type intermediate frequency detecting / amplifying circuit of a receiver, thereby suppressing an increase in cost. Can be. Further, since the received wave is detected by the phase difference, there is an advantage that the possibility of malfunction is extremely low as compared with the conventional method of determining the signal level or the noise level. This leads to the effect that it is not necessary to use a filter having a high selectivity in order to prevent malfunction of the carrier detection device. Therefore, according to the present invention, it is possible to provide a carrier detection device that is less likely to malfunction and that can suppress an increase in the cost of the receiver.

[Brief description of the drawings]

FIG. 1 is a block diagram of a part of a circuit constituting a receiver and an embodiment of a carrier detection device according to the present invention.

FIG. 2 is a block diagram of a part of circuits constituting a receiver and a first example of a conventional carrier detection device.

FIG. 3 is a block diagram of a part of a circuit constituting a receiver and a second example of a conventional carrier detection device.

[Explanation of symbols]

 Reference Signs List 5 second frequency mixer 6 second intermediate frequency filter 7 intermediate frequency amplifier 13 loop filter 14 voltage controlled oscillator 16 PLL section D1 carrier detection device

Claims (2)

(57) [Claims] A mixer that mixes a local oscillation frequency with a received high-frequency signal to generate an intermediate frequency signal; a PLL unit that has a phase comparator function and a frequency lock function; In a carrier detection circuit having a voltage-controlled oscillator that changes the frequency, the intermediate frequency of the receiver is used as the lock frequency of the PLL unit, and the frequency of the received signal is in phase with the frequency set by the PLL unit by controlling the frequency of the voltage-controlled oscillator. And a lock signal when the PLL section is in a locked state is used as a carrier detection signal. 2. The carrier detection device according to claim 1, wherein the control range of the frequency of the voltage controlled oscillator is controlled to a frequency range corresponding to an allowable range of the frequency of a signal to be transmitted and received.