JPS61105155A - Frequency switching circuit - Google Patents

Abstract

PURPOSE:To prevent transmission efficiency from deteriorating by detecting the edge of square wave output of a waveform changing circuit, inputting the timing pulse of the edge to an FF circuit, and switching the frequency at the zero cross point nearest from the arrival of a switching signal. CONSTITUTION:When a mark signal M in a switching signal A is given to a switching input terminal 16, an FF10 generates output Q. At that time the operating current runs from a current switching circuit 6 to a resistance 8A side, and a VCO 2 oscillates the frequency f1 determined by a capacitor 4 and resistance 8A and it is converted into square wave B by a waveform changing circuit 14. An edge detecting circuit 20 detects the edge, generates the timing pulse C and adds it to the clock input CK of an FF10. When a space signal S of A is given to a terminal 16, the VCO 2 oscillates frequency f2. And the pulse C corresponding to the f2 is added to the FF10. In this frequency switching operation, the frequency is changed at the timing pulse arrival closest to the point when the switching signal A is changed from M to S, i.e. at the arrival of the closest zero cross point of the waveform oscillated by the VCO 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is installed in, for example, a data premises equipment or information processing equipment of a data communication system, and for data transmission.
This article relates to a frequency switching circuit that switches the oscillation frequency for transmission, etc.

2. Description of the Related Art Generally, a data communication system is equipped with a frequency switching circuit for transmitting frequencies as shown in FIG. That is, a voltage controlled oscillator (VCO) 2 is configured to be able to oscillate two or more frequencies to be transmitted, and a capacitor 4 as a time constant determining element is connected to the VCO 2, and also serves as an oscillation frequency switching circuit. Resistors 8A and 8B are connected via a current switching circuit 6. The capacitor 4 and the resistor 8A or 8B constitute a time constant circuit that determines the frequency to be oscillated, and the current switching circuit 6 is a flip-flop circuit i as switching control means.

Based on the switching control signal from , the currents flowing through the resistors 8A and 8B are selectively switched to set a predetermined time constant for the VCO2. The flip-flop circuit 10 in this case is composed of a D-flip-flop circuit.

The oscillation output of the VCO 2 is taken out to the outside via the output circuit 12 and is converted into a rectangular wave output via the waveform conversion circuit 14, after which it becomes the clock input CK of the flip-flop circuit 10.

The switching signal applied to the switching input terminal 16 is applied to the data input of the flip-flop circuit 10 via the switching circuit 18.

According to such a frequency switching circuit, for example, a mark, a space (M/
High and low level signals corresponding to S) are selectively added.

E in FIG. 6 shows these mark signals (M) and space signals (S). Such a switching signal is applied to the data input of the flip-flop circuit 10 via the switch circuit 18, and when the mark signal is switched to the space signal at a certain point, the flip-flop circuit 10 causes its non-inverting output Q to be inverted. Switch to output page.

For example, when the flip-flop circuit 10 is switched from the non-inverted output Q to the inverted output page, assuming that the operating current flowing from the current switching circuit 6 to the resistor 8A side flows to the resistor 8B side, the VCO 2 and resistance 8A
The frequency f2 is based on the time constant determined by the capacitor 4 and the resistor 8B.
The oscillation frequencies f, f2 are selectively taken out from the output circuit 12 and converted into a rectangular wave via the waveform conversion circuit 14, and then become the clock input CK of the flip-flop circuit 10. .

F in FIG. 6 shows the waveform shaping output of the waveform conversion circuit 14, and G in FIG. 6 shows the oscillation frequency waveform obtained via the output surface path 12.

Problems to be Solved by the Invention In such a frequency switching circuit, the rise of the rectangular wave output of the waveform conversion circuit 14 is synchronized with the zero cross point of the oscillation output of the VCO 2, so the leading edge of the rectangular wave output is flip-flopped. If the clock input CK of the pull-up circuit 1o is
As shown in the figure, there is an advantage that the frequency can always be switched at the zero-crossing point of the oscillation output. That is, switching the frequency at such a zero-crossing point can prevent bit errors on the receiving side, and is useful for preventing malfunctions on the receiving side due to harmonic components that occur when switching in the middle of a waveform.

However, such frequency switching at a zero-crossing point means that the switching timing is performed after waiting for the arrival of the zero-crossing point, and apart from the rare case that the zero-crossing point arrives by chance, the frequency switching at the zero-crossing point is performed by waiting for the arrival of the zero-crossing point. Since this method requires a delay time of

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a frequency switching circuit that enables frequency switching at the zero-crossing point closest to the arrival of a switching signal and prevents a decrease in transmission efficiency.

Means for Solving the Problems That is, the present invention provides an oscillator capable of oscillating two or more different frequencies, a switching circuit for switching the oscillation frequency of this oscillator, and a waveform for converting the oscillation output from the oscillator into a rectangular wave. a conversion circuit; an edge detection circuit that detects the edge of the output waveform of the waveform conversion circuit and generates a pulse; and a flip-flop circuit that applies an inverted output or a non-inverted output to the switching circuit as a switching control input.

Accordingly, the present invention detects the edges of the rectangular wave output of the waveform conversion circuit, the rising and falling points of the rectangular wave using an edge detection circuit, and converts the pulses detected by the edge detection circuit, that is, the timing pulses of the edges, into a flip-flop circuit. By using the clock input CK of the loop circuit, frequency switching is performed at the zero-crossing point closest to the arrival of the switching signal.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the frequency switching circuit of the present invention, and the same parts as those of the frequency switching circuit of FIG. 5 are given the same reference numerals.

In FIG. 1, this frequency switching circuit has an edge on the output side of a waveform conversion circuit 14 that converts the waveform of the oscillation output of VC02 into a rectangular wave, which detects the rise and fall of the rectangular wave output and generates a pulse. A detection circuit 20 is installed, and this edge detection circuit 20 uses a timing pulse generated in synchronization with the edge of the rectangular wave output of the waveform conversion circuit 14 as the clock input CK of the flip-flop circuit 10.

Based on the above configuration, its operation will be explained with reference to FIG.

When the mark signal (M) among the switching signals shown in FIG. 2A is applied to the switching input terminal 16, the flip-flop circuit 10 generates a non-inverted output Q. At this time, an operating current flows from the current switching circuit 6 to the resistor 8A side, and the VCO 2 oscillates at a frequency r determined by the capacitor 4 and the resistor 8A, and this oscillation output is outputted via the output circuit 12. At the same time, it is applied to the edge detection circuit 20 via the waveform conversion circuit 14. The edge detection circuit 20 generates pulses synchronized with the rise and fall of the rectangular wave output. This pulse is transmitted to the flip-flop circuit 10
clock input GK.

Furthermore, when the switching input terminal 16 is supplied with a space signal (S) among the switching signals shown at A in FIG. 2, the flip-flop circuit 10 generates an inverted output page. At this time,
The operating current flows from the current switching circuit 6 to the resistor 8B side, and the VC
O2 oscillates at a frequency f2 determined by capacitor 4 and resistor 8B, and this oscillation output is output via output circuit 12 and is also applied to edge detection circuit 20 via waveform conversion circuit 14. In this case as well, the edge detection circuit 20 generates pulses synchronized with the rise and fall of the rectangular wave output. This pulse is
It is applied to the clock input CK of the flip-flop circuit 10.

In such a frequency switching operation, B in FIG. 2 is the rectangular wave output of the waveform conversion circuit 14, C in FIG. 2 is the timing pulse of the edge detection circuit 20, and D in FIG. 2 is the output circuit 12.
The oscillation outputs of VCO2 obtained through the oscillation outputs are shown respectively.

As is clear from the waveform in FIG. 2, the edge detection circuit 20 adds pulses corresponding to the edges of the rectangular wave output of the waveform conversion circuit 14 to the clock input CK of the flip-flop circuit 10, so that circuit 10
The switching of the operation corresponds to the edge of the rectangular wave output of the waveform conversion circuit 14. That is, in response to the arrival of the timing pulse closest to the time when the switching signal shown at A in FIG. Frequency can be switched.

Therefore, the delay of a maximum of one cycle of the oscillation waveform in the frequency switching circuit shown in FIG. 5 is reduced to the maximum cycle, and transmission efficiency is improved.

FIG. 3 shows a specific example of the configuration of the edge detection circuit 20. This edge detection circuit 20 has an exclusive O
A delay circuit consisting of inverters 24 and 26 is added to one terminal of the R circuit 22, and an exclusive O
Edge detection of the rectangular wave output is performed by directly applying the rectangular wave output of the waveform conversion circuit 14 to one terminal of the R circuit 22 and applying it to the other terminal via the inverter 24,26.

Therefore, if the waveform shown in FIG. 26 and delayed by a small amount of time
Since the rectangular wave output shown in E in the figure is added, the exclusive OR circuit 22 receives the edge of the rectangular wave output from the waveform conversion circuit 14 as shown in C in FIG. A thin timing pulse corresponding to the

Therefore, this output pulse is transferred to the flip-flop circuit I
By using a clock input CK of 0, the frequency can be switched in response to the arrival of the nearest zero-crossing point of the oscillation waveform, as shown in FIG. 2 OA to C.

Further, the edge detection circuit 20 can be configured with a differentiating circuit that differentiates the rectangular wave output of the waveform conversion circuit 14, and can also form pulses corresponding to edges of the rectangular wave output.

In the embodiment, switching of the transmission frequency in a data communication system was explained as an example, but the present invention can be used in various oscillation circuits that switch a plurality of frequencies in synchronization with the zero-crossing point of the oscillation waveform. can.

As described in detail, according to the present invention, frequency switching can be performed by detecting the nearest zero-crossing point of an oscillation waveform from the arrival of a switching signal, and, for example, a decrease in transmission efficiency can be suppressed in a data communication system. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the frequency switching circuit of the present invention, FIG. 2 is an explanatory diagram showing its operating waveforms, FIG. 3 is a circuit diagram showing a specific example of the configuration of the edge detection circuit, and FIG. FIG. 4 is an explanatory diagram showing its operating timing, FIG. 5 is a block diagram showing a general frequency switching circuit, and FIG. 6 is an explanatory diagram showing its operating waveform. 2... Voltage controlled oscillator, 6... Current switching circuit as a switching circuit, 10... Flip-flop circuit, 14...
... Waveform conversion circuit, 20... Edge detection circuit. Figure 2, number 3! I 4i1 Figure 5 Figure 6

Claims (2)

[Claims] (1) An oscillator capable of oscillating two or more different frequencies, a switching circuit that switches the oscillation frequency of this oscillator, a waveform conversion circuit that converts the oscillation output from the oscillator into a rectangular wave, and an output waveform of the waveform conversion circuit. an edge detection circuit that detects the edge of and generates a pulse; the output pulse of this edge detection circuit is used as a clock input, and the switching signal of the oscillation frequency is used as a data input, and its inverted output or non-inverted output is sent to the switching circuit. A frequency switching circuit comprising a flip-flop circuit added as a switching control input. (2) the edge detection circuit includes a delay circuit that delays the rectangular wave output generated by the waveform conversion circuit by a minute amount of time;
It consists of an exclusive OR circuit whose one input is the rectangular wave output from the waveform conversion circuit and whose other input is the rectangular wave output obtained through the delay circuit, and edge correspondence is applied to the rectangular wave output by exclusive OR. 2. The frequency switching circuit according to claim 1, wherein the frequency switching circuit generates a timing pulse that is equal to or more than 100%.