JPH11331005A - Waveform shaping circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid delays in rising and falling. SOLUTION: A current flows to a diode D by a potential difference produced between an input and an output of a time constant circuit 20 in the case of rising, a capacitor C is charged and an electric potential at an output terminal OUT rapidly rises. In the case of falling, an output of an amplifier AMP rises by the potential difference produced between the input and the output of the time constant circuit 20, a transistor TR is turned on to rapidly decrease the potential at the output terminal OUT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a device for receiving a burst signal, for example, a PHS (Personal Handy-phone System).
Circuits used as part of the carrier sense circuit in slave stations, especially RSSI (Receiving Signal Strength Ind
icator) relates to a circuit for shaping a signal.

[0002]

2. Description of the Related Art In the PHS, 625 is used.
Communication is performed using a burst signal having a time length of μs, and the PHS slave station needs to quickly and accurately detect the arrival of the burst signal and respond to it. As shown in FIG. 2, a time constant circuit 20 including a resistor R and a capacitor C is provided at a subsequent stage of the receiver 10, and the RSSI signal is input from the receiver 10 to the time constant circuit 20 via the RSSI signal input terminal IN.
I signal is input, and the input RSSI signal is converted to a time constant circuit 2
If the signal is integrated by 0 and supplied to the subsequent stage from the RSSI signal output terminal OUT, amplitude fluctuations appearing in the RSSI signal due to the influence of QPSK modulation, noise, and the like can be suppressed. Signal arrival can be detected stably.

The conventional circuit shown in FIG. 2 has an advantage that the amplitude fluctuation of, for example, about ± 7 dB that appears at the RSSI signal input terminal IN can be reduced to about ± 1 dB, but the time constant circuit 20 is used. Therefore, there is a problem that a delay occurs when the RSSI signal rises and falls. This delay is about 100 μs as shown in FIGS. 3A and 3B.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the problem of the conventional circuit at the time of rising and falling while maintaining the smoothing function of the conventional circuit, and to more accurately output the burst signal as compared with the conventional circuit. The aim is to detect the arrival and respond quickly to it.

In order to achieve the above object, according to the present invention, an RSSI signal indicating a reception level of a burst signal is input from an RSSI signal input terminal thereof, the waveform is shaped, and an RSSI signal after the waveform shaping is output. In the shaping circuit,
(1) a time constant circuit that is connected between the RSSI signal input terminal and the RSSI signal output terminal and integrates the RSSI signal with a predetermined time constant; and (2) the potential of the RSSI signal input terminal is R
A bypass circuit for detecting that the potential is higher than the potential of the SSI signal output terminal by a predetermined value or more, and bypassing the time constant circuit to connect the RSSI signal input terminal to the RSSI signal output terminal; Is detected to be higher than the potential of the RSSI signal input terminal by a predetermined value or more, and an output reduction circuit for forcibly reducing the potential of the RSSI signal output terminal is provided.

As described above, the potential of the RSSI signal output terminal is forcibly raised by the bypass circuit at the time of rising, and the potential of the RSSI signal output terminal is forcibly lowered by the output reduction circuit at the time of falling. According to this, a waveform shaping circuit having less delay at rising and falling times as compared with the conventional circuit can be obtained. Furthermore, since the smoothing by integration is performed by the time constant circuit from the rising to the falling, a smoothness equal to or higher than that of the conventional circuit can be realized. Further, since the potential of the RSSI signal input terminal and the output terminal, that is, the potential before and after the time constant circuit is detected, unlike the circuit described in JP-A-9-261188,
There is no need to detect or estimate the burst timing,
The circuit configuration is simplified.

Furthermore, since the functions relating to the bypass circuit and the output reduction circuit can be realized by diodes and transistors, the circuit configuration is simplified in this respect as well. That is, a bypass circuit can be realized by a diode whose anode is connected to the RSSI signal input terminal and whose cathode is connected to the RSSI signal output terminal. Further, by connecting the output terminal of an amplifier that detects and amplifies the potential difference between the RSSI signal output terminal and the RSSI signal output terminal to the base of the transistor whose collector and emitter are connected to the RSSI signal output terminal and the ground, the output is reduced. A circuit can be realized. Further, since the capacitor in the time constant circuit is charged by the current of the diode at the time of rising speed, unlike the circuit described in JP-A-9-261188,
There is no need to provide a separate charge circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the following description, PH
Although an S carrier sense circuit is taken as an example, the present invention can be applied to various applications that require accurate detection of the rising and falling timings and reception levels of burst signals.

FIG. 1 shows a circuit configuration according to an embodiment of the present invention. In this embodiment, a diode D is connected from the RSSI signal input terminal IN to the RSSI signal output terminal OUT, that is, in the forward direction. In addition, RSS
The resistor Ri1 is connected to the I signal input terminal IN, that is, the input side of the time constant circuit 20, and the RSSI signal output terminal OUT, that is, the time constant circuit 2
A resistor Ri2 is connected to the output side of 0. The resistance Ri1 is the input resistance of the non-inverting input terminal of the amplifier AMP, and the resistance Ri2 is the input resistance of the inverting input terminal of the amplifier AMP. The output terminal of the amplifier AMP is connected to the base of the transistor Tr. The collector of the transistor Tr is connected to the RSSI signal output terminal OUT via a resistor Ro.
And the emitter is grounded. Note that the resistor Rf is a feedback resistor from the output terminal of the amplifier AMP to the inverting input terminal.

In this embodiment, when the potential of the RSSI signal input terminal IN rises sharply with the rise of the burst signal, a current flows through the diode D. That is, since the time constant circuit 20 has a response delay, even if the potential of the RSSI signal input terminal IN rises sharply, the RSSI signal output terminal O
The potential of the UT does not immediately rise, and thus a potential difference transiently occurs before and after the time constant circuit 20. When a current flows through the diode D due to this potential difference, the capacitor C is charged by the current, and the potential of the RSSI signal output terminal OUT rises. As described above, the capacitor C is charged by the forward current of the diode D bypassing the time constant circuit 20, so that the rising edge of the burst signal causes the RSSR to rise.
The potential of the I signal output terminal OUT can quickly rise.

[0011] Further, when the burst signal falls, RSS
When the potential of the I signal input terminal IN sharply drops, the amplifier A
As a result, the potential at the inverting input terminal of MP drops sharply,
The potential at the output terminal of MP rises. That is, the time constant circuit 20
Has a response delay, the potential of the RSSI signal output terminal OUT does not immediately decrease even if the potential of the RSSI signal input terminal IN drops sharply.
Before and after the potential difference. The amplifier AMP is means for detecting and amplifying this potential difference. When the potential at the output terminal of the amplifier AMP becomes equal to or higher than the ON voltage of the transistor Tr, the transistor Tr is turned on and the RSSI signal output terminal OUT is grounded. As described above, when the potential difference equal to or more than the value corresponding to the ON voltage of the transistor Tr is detected, the RSSI signal output terminal OU
Since the potential of T is forcibly reduced, the potential of the RSSI signal output terminal OUT can quickly fall when the burst signal falls.

FIG. 3C shows a waveform after shaping obtained in this embodiment. The delay at the time of rising and falling in this embodiment is only about 20 μs, which is larger than the output of the receiver 10 of about 10 μs in the waveform of FIG. This is smaller than about 100 μs in the waveform of FIG. 3B. Furthermore, since the time constant circuit 20 has an integrating / smoothing effect, the amplitude is almost the same as that of the conventional circuit as long as the fluctuation at the RSSI input terminal IN is equal to or less than the ON voltage of the transistor Tr.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a waveform shaping circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a waveform shaping circuit according to one related art.

3A and 3B are diagrams showing a waveform of an RSSI signal, in particular, FIG. 3A shows an input to a waveform shaping circuit, FIG. 3B shows an output of a conventional circuit, and FIG. FIG.

[Explanation of symbols]

10 receiver, 20 time constant circuit, D diode, A
MP amplifier, Tr transistor.

Claims (3)

[Claims] 1. An RSS indicating a reception level of a burst signal.
A waveform shaping circuit for inputting the I signal from the RSSI signal input terminal and shaping the waveform and outputting the RSSI signal after the waveform shaping, wherein the predetermined signal is connected between the RSSI signal input terminal and the RSSI signal output terminal, A time constant circuit that integrates the RSSI signal with a time constant, and detects that the potential of the RSSI signal input terminal is higher than a potential of the RSSI signal output terminal by a predetermined value or more, and accordingly, bypasses the time constant circuit. A bypass circuit connecting the RSSI signal input terminal to the RSSI signal output terminal, and detecting that the potential of the RSSI signal output terminal is higher than the potential of the RSSI signal input terminal by a predetermined value or more. A waveform shaping circuit comprising: an output lowering circuit for forcibly lowering a potential of a signal output terminal. 2. The waveform shaping circuit according to claim 1, wherein said bypass circuit is a diode whose anode is connected to said RSSI signal input terminal and whose cathode is connected to said RSSI signal output terminal, respectively. Waveform shaping circuit. 3. The waveform shaping circuit according to claim 1, wherein the output reduction circuit detects and amplifies a potential difference between the RSSI signal input terminal and the RSSI signal output terminal, and the collector and the emitter include the amplifier. A transistor having an RSSI signal output terminal, a transistor connected to ground, and a base connected to the output terminal of the amplifier, respectively.