JP3917041B2 - Receiving machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiver that receives an ASK-modulated high-frequency signal and detects and extracts square wave data, and more particularly to a receiver suitable for an ETC system (automatic toll collection system).
[0002]
[Prior art]
FIG. 3 shows the main configuration of a conventional receiver applied to an ETC system or the like. The ASK-modulated high-frequency signal is frequency-converted to an intermediate frequency signal of 40 MHz by a frequency converter (not shown), and then input to the logarithmic amplifier 31 in order to expand the dynamic range. After being amplified, it is input to the detector circuit 32. The intermediate frequency signal input to the logarithmic amplifier 31 has a substantially sinusoidal envelope as shown in FIG. Since the logarithmic amplifier 31 performs logarithmic weighting on the level of the input intermediate frequency signal, the signal (detection signal) detected by the detection circuit 32 has an envelope of A as shown in FIG. The waveform looks like a collapse of the positive half cycle of the waveform.
[0003]
The detection signal is input to the waveform shaping circuit 33. The waveform shaping circuit 33 has a comparator 33c. The detection signal is input to one input terminal of the comparator 33c via the resistor 33a, and input to the other input terminal via the integrating circuit 33b. Since the phase of the detection signal input via the integration circuit 33b is delayed, a level difference occurs between the detection signals input to the two input terminals, and the detection signal is converted into a square wave as shown in FIG. However, since the detection signal is crushed as described above, the duty cycle is about 60 to 70%. This square wave becomes data. The square wave is output from the last-stage switch transistor TR in the comparator 33c. A power supply voltage is supplied to the collector of the transistor TR via a power supply resistor R.
[0004]
[Problems to be solved by the invention]
The duty cycle of the square wave output from the waveform shaping circuit is required to be a predetermined value, for example, 50% because of data processing. However, since the ASK-modulated high frequency signal is amplified by the logarithmic amplifier, it is not necessarily 50. There was a problem that it was not%.
[0005]
An object of the present invention is to provide a receiver capable of accurately adjusting the duty cycle of a detected square wave to a predetermined value, for example, 50%.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a logarithmic amplifier that amplifies an ASK-modulated high-frequency signal by logarithmic weighting, a detection circuit that detects an envelope of the amplified high-frequency signal, and the detection circuit A waveform shaping circuit that shapes the detection signal output from the waveform into a square wave, and the waveform shaping circuit includes a switch transistor that applies a power supply voltage to the collector via a feeding resistor and outputs the square wave from the collector. And a switching circuit that is turned on or off at a specific threshold level is connected to the collector of the switch transistor, and the collector of the switch transistor is grounded through a capacitive element.
[0007]
Further, the switching circuit is constituted by an inverter.
[0008]
A resistor is connected between the collector of the switch transistor and the capacitive element.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The main configuration of the receiver of the present invention is shown in FIG. The ASK-modulated high frequency signal is frequency converted into a 40 MHz intermediate frequency signal by frequency conversion means (not shown). The intermediate frequency signal is input to the logarithmic amplifier 1 to expand the dynamic range, and is amplified and then input to the detection circuit 2. The intermediate frequency signal input to the logarithmic amplifier 1 has a substantially sinusoidal envelope as shown in FIG. Since the logarithmic amplifier 1 performs logarithmic weighting on the level of the input signal, the signal (detection signal) detected by the detection circuit 2 has the waveform of the envelope of A as shown in FIG. The waveform looks like a collapse of the positive half cycle.
[0010]
The detection signal is input to the waveform shaping circuit 3. The waveform shaping circuit 3 includes a comparator 3c, and the detection signal is input to one input terminal of the comparator 3c via the resistor 3a and input to the other input terminal via the integrating circuit 3b. The phase of the detection signal input via the integration circuit 3b is delayed, resulting in a level difference between the detection signals input to the two input terminals. The detection signal has a duty cycle of 60 as indicated by C in FIG. It is converted into a square wave of about 70%. This square wave becomes data. The square wave is output from the last-stage switch transistor TR in the comparator 3c. A power supply voltage is supplied to the collector of the transistor TR via a power supply resistor R.
[0011]
A switching circuit 5 is connected to the waveform shaping circuit 3 via a time constant circuit 4. The time constant circuit 4 is composed of, for example, an integrating circuit composed of a resistor 4a and a capacitive element 4b, and the collector of the switch transistor TR in the waveform shaping circuit 3 is grounded by the capacitive element 4b via the resistor 4a. The switching circuit 5 is connected to the connection point between the resistor 4a and the capacitive element 4b. The switching circuit 5 is configured by, for example, an inverter of a logic circuit, and is turned on or off at a specific threshold level.
[0012]
In the above configuration, a square wave that changes between high and low in response to a square wave appearing at the collector of the switch transistor TR appears at the connection point between the resistor 4a and the capacitive element 4b, but the switch transistor TR is turned off. Sometimes, the capacitive element 4b is charged through the power supply resistor R and the resistor 4a, and when the switch transistor TR is turned on, it is discharged through the resistor 4a and the internal resistance of the switch transistor TR. In this case, the square wave has a different rise time and fall time. Since the rise time and the fall time depend on the power supply resistor R, the resistor 4a, the capacitive element 4b, and the internal resistance, the rise time and the fall time can be changed over a wide range, and can cope with variations in the threshold level of the switching circuit.
[0013]
Therefore, by appropriately setting the resistance value of the feeding resistor R, the time when the switching circuit 5 is turned on is changed, and the duty cycle of the output square wave is set to a predetermined value, for example, 50% as shown in E of FIG. Can be set to
[0014]
The resistor 4a may be deleted and the collector of the switch transistor TR may be directly grounded by the capacitive element 4b. In this case, the capacitive element 4b is charged via the power supply resistor R and discharged by the internal resistance of the switch transistor TR.
[0015]
【The invention's effect】
As described above, the present invention provides a logarithmic amplifier that amplifies an ASK-modulated high-frequency signal by logarithmically weighting, a detection circuit that detects an envelope of the amplified high-frequency signal, and an output from the detection circuit. A waveform shaping circuit that shapes the detection signal into a square wave, and the waveform shaping circuit includes a switch transistor that applies a power supply voltage to the collector via a feeding resistor and outputs a square wave from the collector, and has a unique threshold. Since the switching circuit that is turned on or off at the level is connected to the collector of the switch transistor and the collector of the switch transistor is grounded via the capacitive element, the duty cycle of the square wave that is output from the switching circuit depends on the feeding resistor and the capacitive element It can be easily set to a predetermined ratio, for example, 50% depending on the time constant.
[0016]
Further, since the switching circuit is configured by an inverter, the configuration is extremely simple.
[0017]
In addition, since the resistor is connected between the collector of the switch transistor and the capacitive element, the duty cycle can be adjusted regardless of the threshold level of the switching circuit.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a main part of a receiver according to the present invention.
FIG. 2 is a waveform of each part in the receiver of the present invention.
FIG. 3 is a circuit diagram showing a configuration of a main part of a conventional receiver.
FIG. 4 is a waveform of each part in a conventional receiver.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Logarithmic amplifier 2 Detection circuit 3 Waveform shaping circuit 3a Comparator 3b Resistance 3c Integration circuit 4 Time constant circuit 4a Resistance 4b Capacitance element 5 Switching circuit

Claims (3)

A logarithmic amplifier that amplifies the ASK-modulated high-frequency signal by logarithmically weighting, a detection circuit that detects the amplified high-frequency signal by envelope detection, and a waveform shaping of the detection signal output from the detection circuit into a square wave The waveform shaping circuit includes a switch transistor that applies a power supply voltage to the collector via a feeding resistor and outputs the square wave from the collector, and is turned on or off at a specific threshold level. A receiver characterized in that a switching circuit is connected to a collector of the switch transistor and the collector of the switch transistor is grounded via a capacitive element. The receiver according to claim 1, wherein the switching circuit is configured by an inverter. The receiver according to claim 1, wherein a resistor is connected between the collector of the switch transistor and the capacitive element.

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