JPH0611150B2 - Transmission frequency switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is installed in, for example, a data home device or an information processing device of a data communication system,
The present invention relates to a transmission frequency switching device that switches the frequency of a transmission signal.

[Conventional technology]

Conventionally, for example, a transmission frequency switching device shown in FIG. 3 is installed in a data transmission system. In this transmission frequency switching device, the voltage controlled oscillator 2 generates a signal to be transmitted, and the resistors 6A and 6B and the capacitor 8 connected to the voltage controlled oscillator 2 via the switch circuit 4 change the transmission signal frequency. It constitutes the time constant circuit to determine. The switch circuit 4 responds to a switching signal applied to the input terminal 10 to the resistor 6 with respect to the voltage controlled oscillator 2.
Either A or 6B is selected and connected. That is,
If the resistors 6A and 6B are configured to have different resistance values, one of the resistors 6A and 6B for the capacitor 8 is selected and switched, so that the oscillation frequency of the voltage controlled oscillator 2 has two stages according to the resistors 6A and 6B. It will be switched.

Since the signal to be transmitted generated by the voltage controlled oscillator 2 is a triangular wave, it is applied to the waveform shaping circuit 12 and converted into a sine wave waveform, and then applied to the gate circuit 14.

A switching signal according to the transmission / reception mode is applied to the switching input terminal 16, and the switch circuit 18 obtains a gate control signal for controlling the gate circuit 14 in the open state or the closed state according to the switching signal. Therefore, the gate circuit 14 is controlled to be opened in the transmission mode and closed in the reception mode by mode switching by the gate control signal, and the signal to be transmitted is transmitted from the output terminal 20 in the transmission mode.

Next, FIG. 4 shows operation waveforms of this transmission frequency switching device. A is a signal waveform generated by the voltage controlled oscillator 2, H is a switching signal applied to the input terminal 10, and I is a waveform shaping circuit 12 for conversion. The obtained sine wave waveform, J is the gate control signal applied to the gate circuit 14 from the switch circuit 18, and K is the signal waveform passed through the gate circuit 14.

[Problems to be Solved by the Invention]

By the way, in such a transmission frequency switching device, since the time constant of the voltage controlled oscillator 2 is switched according to the switching signal, as shown in A and I of FIG. 4, the low oscillation frequency is switched to the high oscillation frequency. However, a change point appears at the switching point P in I of FIG.

In this way, if the waveform changes at a portion other than the zero-cross point, many harmonic components are generated at the switching portion, which may cause inconvenience such as erroneous reception operation in the receiving side circuit, and the data transmission signal. The waveform is damaged,
There are inconveniences such as a high bit error rate on data.

Therefore, it is an object of the present invention to provide a transmission frequency switching device that suppresses the harmonic component generated at the change point of the oscillation waveform when switching the oscillation frequency.

[Means for Solving the Problems]

As shown in FIG. 1, the transmission frequency switching device of the present invention includes a voltage controlled oscillator that generates a triangular wave having a frequency controlled according to a control voltage, and a sinusoidal wave that generates the triangular wave generated by the voltage controlled oscillator. A first waveform converting circuit for converting into a sine wave, a gate circuit for receiving the sine wave obtained by the first waveform converting circuit, receiving a switch signal and opening / closing to selectively output the sine wave, A second waveform conversion circuit that converts the triangular wave generated by the voltage controlled oscillator into a pulse having a rising edge or a falling edge at the zero-cross point, and the pulse output from the second waveform converting circuit is applied to a clock input. A flip-flop circuit which receives a switching signal for switching the oscillation frequency as a data input and inverts the output after waiting for the arrival of the zero-cross point of the triangular wave; Characterized in that the flip-flop circuit is composed of a switching circuit for switching the frequency of the triangular wave by switching the control voltage in response to the output generated.

[Action]

When a change point occurs between the current oscillation waveform and the previous oscillation waveform due to switching of the oscillation waveform, there are cases where the change point occurs at the zero cross point of the waveform, and where it occurs at points other than the zero cross point of the waveform. It is confirmed that the high frequency component distribution is small when a change point of the waveform occurs at the zero-cross point by comparing the spectrum analyzers with the spectrum analyzer waveform.

Therefore, in the present invention, the switching of the oscillation frequency is set to the zero cross point of the oscillation output, the change point is set to the zero cross point, and the harmonic component at the change point is suppressed. That is, by detecting the zero-cross point of the previous oscillation waveform and using that zero-cross point as the starting point of the next oscillation waveform,
Since the oscillation frequency is switched at the zero cross point, high frequency components are suppressed.

〔Example〕

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

FIG. 1 shows an embodiment of the transmission frequency switching device of the present invention, and the same parts as those of the transmission frequency switching device shown in FIG.

A voltage-controlled oscillator 2 is installed as a signal source for generating a signal to be transmitted, and in this embodiment, for example, two oscillation frequencies are oscillated as a plurality of oscillation frequencies having different frequencies. Resistors 6A and 6B are connected through the first switch circuit 4 as elements for determining the. The switch circuit 4 constitutes connection switching means for selectively connecting the resistors 6A and 6B to the voltage controlled oscillator 2 in response to the control output of the switching control circuit 24. Therefore, the connection of the resistors 6A and 6B to the voltage controlled oscillator 2 is switched by the switch circuit 4, so that the time constant is set according to the resistors 6A and 6B, and the oscillation frequency different from the voltage controlled oscillator 2 depending on the resistors 6A and 6B. Is obtained. For example, the voltage controlled oscillator 24 includes a transistor differential pair as a voltage comparison means, takes out the output current of this transistor differential pair via a buffer circuit for each transistor, converts it into a voltage, and then converts the voltage into a transistor differential pair. A capacitor 8 that feeds back to each base side of the pair and that charges or discharges with the output current is connected between the outputs of the buffer circuit, and the charging voltage of the capacitor 8 controls the extraction of the output current by the buffer circuit. It is configured to be. Resistance 6A,
6B is a means that is connected in series to the transistor differential pair and determines the value of its operating current. Switch circuit 4
Is a means for selecting the resistors 6A and 6B to be connected to the transistor differential pair and switching the operating current of the transistor differential pair. The output current of the transistor differential pair is the value of this operating current, that is, the selected resistors 6A and 6A.
Depending on B, the selection of resistors 6A, 6B will change the charging time of capacitor 8. This appears as the oscillation frequency, that is, the oscillation frequency can be switched by selecting the resistors 6A and 6B.

Then, a second switch circuit 22 is installed corresponding to the switch circuit 4, and the switch circuit 22 obtains a switching signal according to the switching input applied to the input terminal 10,
This switching signal is applied to the switching control circuit 24 as a control input.

The switching control circuit 24 detects a zero cross point of the oscillation output of the voltage controlled oscillator 2 in response to the switching signal of the switch circuit 22, and generates a switching control signal as a control output for the switch circuit 4 at this zero cross point. The switching control circuit 24 is provided with a flip-flop circuit 28 as well as a waveform shaping circuit 26 as a second waveform conversion circuit for converting the oscillation output waveform of the voltage controlled oscillator 2. In the waveform shaping circuit 26, for example, a voltage comparator is used to convert the output waveform of the voltage controlled oscillator 2 into a rectangular wave that falls or rises at its zero cross point. Then, in the flip-flop circuit 28, the waveform shaping circuit 2
Square wave output from 6 is clock input CK, switch circuit 2
A switching signal from 2 is applied to the data input D for switching, and its non-inverted output Q is applied to the switch circuit 4 as a switching control signal.

Then, on the oscillation output side obtained by the voltage controlled oscillator 2,
A waveform shaping circuit 12 as a first waveform conversion circuit is installed, and a waveform shaping output is applied to the gate circuit 14 through the waveform shaping circuit 12. A switch circuit 18 is provided as a control means for controlling the signal passage of the gate circuit 14.

The operation of the above configuration will be described with reference to FIG.

The voltage controlled oscillator 2 generates a frequency signal shown by A in FIG. 2 by its oscillating operation. The voltage controlled oscillator 24 includes a transistor differential pair that converts an output current into a voltage and is fed back to the base side. Each transistor of the transistor differential pair is a voltage fed back to the base and the capacitor 8 is charged. The cutoff state is selectively controlled by the voltage. In the waveform of FIG. 2A, the stable region indicates the charging period of the capacitor 8, the steep rising or falling period indicates the switching period of the transistor of the transistor differential pair, and the slanting region indicates the discharging period of the capacitor 8. Differential pair operating current, ie selected resistor 6
Depends on A and 6B. This oscillating signal is generated by the waveform shaping circuit 2
6B, the waveform is shaped into a rectangular wave that falls at the zero-cross point of the triangular wave shown in A of FIG. 2 as shown in B of FIG.
As shown in C of the figure, it is converted into a sine wave waveform. The latter sine wave is applied to the gate circuit 14 as the signal to be transmitted.

Also, the former rectangular wave output becomes the clock input CK of the flip-flop circuit 28, and in response to the switching input applied to the input terminal 10, the switching signal (low level portion) shown in D of FIG. Circuit 2
8 data input D. Therefore, the non-inverted output Q of the flip-flop circuit 28 corresponds to the clock input CK and the switching signal, as shown at E in FIG. 2, and rises (H) and falls (L).
Corresponds to the fall of the rectangular wave shown in B of FIG. 2 that is closest to the fall of the switching signal shown in D of FIG.

Then, the switching signal is converted by the switching control circuit 24 into a switching control signal synchronized with the zero-cross point of the oscillation waveform generated by the voltage controlled oscillator 2, and applied to the switch circuit 4.

Therefore, in the transmission mode, the switch circuit 4 is switched at the zero-cross point of the oscillation waveform closest to the leading edge of the switching signal. In this case, either the resistor 6A or the resistor 6B is selected and the predetermined time constant is set. It As a result, the second
As shown in C of the figure, the switching of the oscillation frequency is performed at the zero-cross point P of the oscillation waveform, and the oscillation waveform of different frequency having smooth switching is obtained at the zero-cross point.

The gate circuit 14 responds to the switching input applied from the switching circuit 18 to the switching input terminal 16, and the switching signal shown in F of FIG.
In this high (H) level section, the transmission mode is opened and the transmission waveform shown by G in FIG. 2 is output from the output terminal 20.

Further, in this embodiment, since the zero-cross point of the oscillation waveform is directly detected from the output waveform of the voltage controlled oscillator 2, accurate detection can be realized, but as another method, the zero-cross point from the output of the waveform shaping circuit 12 can be obtained. Even if the points are detected, the same effect can be expected.

〔The invention's effect〕

As described above, according to the present invention, since the oscillation frequency is switched at the zero-cross point of the oscillation waveform, it is possible to suppress the generation of harmonic components due to the frequency switching, and it is possible to prevent malfunctions due to the harmonic components on the receiving side. The occurrence can be prevented and the bit error rate can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission frequency switching device of the present invention, FIG. 2 is a diagram showing operation waveforms of the transmission frequency switching device shown in FIG. 1, and FIG. 3 is a conventional transmission frequency switching device. And FIG. 4 is a diagram showing operation waveforms of the transmission frequency switching device shown in FIG. 2 ... Voltage controlled oscillator 4 ... Switch circuit 12 ... Waveform shaping circuit (first waveform conversion circuit) 14 ... Gate circuit 26 ... Waveform shaping circuit (second waveform conversion circuit) 28 ... Flip-flop circuit

Claims (1)

[Claims] 1. A voltage controlled oscillator for generating a triangular wave having a frequency controlled according to a control voltage; a first waveform conversion circuit for converting the triangular wave generated by the voltage controlled oscillator into a sine wave; Receiving the sine wave obtained by the waveform conversion circuit of 1,
A gate circuit that receives and outputs a switch signal to selectively output the sine wave; and a second circuit that converts the triangular wave generated by the voltage controlled oscillator into a pulse having a rising or falling at a zero-cross point thereof.
And the pulse output from the second waveform conversion circuit is applied to the clock input, and the switching signal for switching the oscillation frequency is applied as the data input to wait for the arrival of the zero-cross point of the triangular wave. And a switch circuit for switching the frequency of the triangular wave by switching the control voltage according to the output generated by the flip-flop circuit. apparatus.