JPH0897658A - Multi-rate signal filter changeover circuit - Google Patents

Abstract

PURPOSE: To eliminate missing or space of data at changeover and to prevent the circuit scale from being increased by improving a changeover circuit placing a band limit corresponding to a rate in the case of multi-rate transmission. CONSTITUTION: The input of a system comprising a 1st delay circuit 2 and a 1st LPF 3 or of a system comprising a 2nd delay circuit 4 and a 2nd LPF 5 is selected by a changeover device 1 every time a data transmission speed is changed and the output is added by an adder circuit 6 and obtained. A control section 7 changes a cut-off frequency of the selected LPF based on changeover information and sets a delay not affecting output data of the disconnected delay circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a transmitter for switching and transmitting multi-rate signals having different data transmission rates in the communication of the same modulation system, and the cutoff frequency of a filter corresponding to the selected transmission rate. The present invention relates to a filter switching circuit that switches a bandwidth, a bandwidth, and the like to limit a band of a baseband signal before modulation and output the baseband signal.

[0002]

2. Description of the Related Art Usually, the same communication method (FSK, PSK) is used.
Etc.), the lower the transmission rate, the better the various communication characteristics. Utilizing this, for example, for information that is important for communication such as control signals and synchronization signals, use a low-quality transmission rate with good quality, and switch the normal information signal to a high transmission rate to obtain the amount of information. Or more
Depending on the congestion of the communication network, you can use a low quality transmission rate with good quality when the line is free, and switch to a higher transmission rate when the line gets crowded to eliminate the line congestion and reduce the holding time. Has been done. In the above case, for example, 1200 bps, 2400 bps, 480
Something that has a multiplication relationship such as 0 bps, or 9600 b
Several types of transmission rates (multirates), such as those having a fixed ratio relationship such as ps and 14400 bps, are set in advance, and the control device or the like on the transmission side or the master side switches. As a method of switching, the transmitting side or the master side puts the speed information at a predetermined transmission rate and periodically transmits, and the receiving side or the slave side changes the speed based on the received information, and There is a method of switching the transmission rate for each predetermined timing, and the transmission is performed by band limiting with an LPF (low-pass filter) having a cutoff frequency corresponding to the switched transmission rate.

FIG. 3 is a diagram showing a configuration example of a conventional circuit.
Is a circuit using a switched capacitor filter (hereinafter referred to as SCF) 10. The SCF 7 is an analog filter that can control the cutoff frequency with a control clock that is several tens of times the cutoff frequency. The input signal is a multi-rate signal input by switching a plurality of types of transmission rates. When the cutoff frequency of the SCF 7 is changed according to the transmission rate, it can be set to a desired value by changing the frequency of the control clock according to the transmission rate.

FIG. 4 is a diagram showing an example of a filter switching circuit which is another example of the conventional circuit. In the figure, switching devices 14 and 15
Thus, n low-pass filters (hereinafter referred to as LPFs) 11 to 13 having different cutoff frequencies are switched and used. The delay amounts of these plural LPFs are adjusted in advance so that the signal timings after passing through the respective filters are the same.

[0005]

However, the SCF
Since the delay time changes depending on the cutoff frequency, it is difficult to make the timing of the zero level crossing point after passing through the filter the same as the timing before passing through the filter due to the nature of the filter. Further, even if a delay circuit is provided at the input of the SCF and the delay time is adjusted according to the transmission speed, the input data is interrupted halfway when changing from a long delay time to a short delay time, and conversely the delay time is short. There is a problem that the same input data is repeated when changing from a long one to a long one. Even if a digital filter is used instead of the SCF 7, the cutoff frequency can be changed by changing the oversampling frequency of the filter as well. However, even with a digital filter, the output signal is delayed to some extent and the digital filter is controlled. When the clock is changed, the time relationship of the output signals also changes in synchronization with the control clock, so the output waveform switches before the output of the signal at the transmission rate before the change ends, which is the original purpose. The result is different from the cutoff control for each transmission rate. Even if a delay circuit is provided at the input like the SCF and the delay time is adjusted according to the transmission speed, the input data may be interrupted when the delay time changes from a long delay time to a short delay time, or conversely There is a problem that the same input data is repeated when changing from short to long.

Further, when the cutoff frequency is fixed, it is possible to control the frequency of the least common multiple of each frequency as the reference clock, which is the same as when only one LPF is used. Also, when changing the parameters of the digital filter (when the characteristics of the filter are different), the output waveform changes when the parameters are gradually changed. It is necessary to use a filter, and such a filter can be realized. If the bandwidth is B, the period of one symbol (= 1 / transmission rate) is T _s , and the BT product is constant, if the characteristics are constant, if the ratio of the transmission rate and the control clock is kept constant, control is performed. I will. However, even with a digital filter, the output signal is delayed to some extent, and when the digital filter changes the control clock, the time relationship of the output signal changes in synchronization with the control clock.
The output waveform is switched before the output of the transmission speed signal before the switching is completed. Therefore, the original purpose is different from the cutoff control for each transmission rate, and this is the most serious problem.

Further, in the case of FIG. 4, there is a problem that the circuit scale becomes large because a large number of filters and delay circuits are required corresponding to various transmission rates.

An object of the present invention is to improve the above-mentioned problems of the prior art, eliminate data loss and blank at the time of transmission rate switching,
It is an object of the present invention to provide a multi-rate signal filter switching circuit having a relatively small circuit configuration for a large number of transmission rates.

[0009]

A multi-rate signal filter switching circuit according to the present invention includes a switching device for switching and outputting an input signal to either a first output terminal or a second output terminal according to a select signal, and the switching device. Delay circuit for delaying the signal from the first output terminal of the switching device by the delay amount set by the delay time control signal and outputting the signal from the second output terminal of the switching device A second delay circuit that delays by a delay amount set by the signal and outputs the delayed signal;
A first LPF that outputs the output of the first delay circuit by band limiting at a cutoff frequency set by a cutoff control signal, and the output of the second delay circuit are set by a cutoff control signal. A second LPF that outputs a band-limited signal at a cutoff frequency, and the first and second LPFs
The select signal, the delay time control signal, and the cutoff control signal are output by a combining circuit that adds and outputs the LPF output and speed switching information that is given at the same time when the data transmission speed of the input signal is switched. And a control unit that, each time the data transmission rate of the input signal is switched, gives the select signal to the switch and switches the output of the switch to the other,
A cutoff control signal for setting a cutoff frequency for band limiting corresponding to the data transmission rate is given to the LPF on the switched side, and the LPF on the separated side is supplied to the delay circuit on the switched side. The present invention is characterized in that a delay time control signal for setting a delay amount that does not affect the output data is given.

[0010]

1 is a block diagram showing an embodiment of the present invention.
In the figure, 1 is a switcher for switching and outputting an input signal according to a select signal, 2 and 4 are a first delay circuit and a second delay circuit whose input signal delay amount can be arbitrarily changed by a control signal, and 3 and 5 A first LPF and a second LF whose cutoff frequency is arbitrarily set by a cutoff control signal
PF, 6 is a synthesizing circuit for synthesizing the outputs of the first LPF 3 and the second LPF 5 into an output signal, and 7 is a select signal, a delay time control signal, a cutoff control signal each time the speed is switched by speed switching information. Is a control unit for outputting.

[0011]

The operation of the present invention based on the configuration example shown in FIG. 1 will be described with reference to FIG.
Will be explained. FIG. 2 is a time chart for explaining the operation of the present invention, and is a timing chart showing input / output signals when the input signal in FIG. 1 once changes the transmission rate and then switches back to the original transmission rate. In the figure, for the sake of explanation, there is no problem in operation regardless of whether the signal form is digital or analog, and therefore the explanation will be given as an analog waveform. Speed switching information is RATE, RATE
, RATE are switched in this order. The control unit 7 outputs a select signal, a delay time control signal, and a cutoff control signal each time the speed is switched, based on the speed switching information. The select signal changes at the same time as the speed is switched, and the delay time control signal and the cutoff control signal are output after being sufficiently delayed so that the output of the LPF on the switched side of the input signal is not affected. It The input signal is a first signal LPF3, a second signal LPF5, and a second signal LPF5 via a delay circuit each time the transmission speed is switched by a select signal for switching control of the switch 1.
Switching is performed in the order of the first LPF 3, and the output of the first delay circuit 2 and the output of the second delay circuit 4 are as illustrated.
A zero-level signal is set in the no-signal section due to switching. First
The LPF 3 and the second LPF 5 change the cutoff frequency by the cutoff control signal at the timing when their inputs do not affect the filter output in the no signal section. At the same time, the delay amounts of the first delay circuit 2 and the second delay circuit 4 are changed in the same manner as in the case of the LPF so that the timing of the signal after waveform synthesis becomes the same as before the filter input. Normally, switching of the transmission rate is not performed at short intervals, so that control for each filter can be performed with a margin. 1st LPF3 which passed each filter
The waveforms of the output and the output of the second LPF 5 are combined by the combining circuit 6 and output as an output signal. The description has been given for the LPF, but the same control can be performed in a filter switching circuit in the case of a bandpass filter (BPF) or the like. Since the amount of delay of the filter varies depending on the cutoff frequency, the synthetic waveform causes swelling or shrinking of the waveform at the change point of the transmission rate, but this may be left as it is as long as there is no problem in operation.

[0012]

As described above, according to the present invention, control of a plurality of cutoff frequencies can be configured by two programmable filters and delay circuits, and it is not necessary to provide a large number of filters and delay circuits. Further, both a digital filter and an analog filter such as SCF can be easily realized, and the delay amount can be controlled relatively easily.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration example of the present invention.

FIG. 2 is a timing chart showing the operation of the present invention.

FIG. 3 is a diagram illustrating a configuration example of a conventional circuit.

FIG. 4 is a diagram showing another configuration example of a conventional circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 switching device 2 1st delay circuit 3 1st LPF 4 2nd delay circuit 5 2nd LPF 6 synthetic | combination circuit 7 control part 10 SCF 11 1st LPF 12 2nd LPF 13 nLPF 14 and 15 switching device

Claims (1)

[Claims] 1. A switcher for switching and outputting an input signal to either a first output terminal or a second output terminal according to a select signal, and a signal from the first output terminal of the switcher is a delay time control signal. A first delay circuit for delaying and outputting by a delay amount set by, and a second delay circuit for delaying and outputting a signal from the second output terminal of the switcher by a delay amount set by a delay time control signal. Delay circuit, a first LPF that outputs the output of the first delay circuit by band limiting at a cutoff frequency set by a cutoff control signal, and cutoff control of the output of the second delay circuit. A second LPF for band-limiting and outputting at a cutoff frequency set by a signal; a combining circuit for adding and outputting the outputs of the first and second LPFs; and a data transmission rate of the input signal. And a control unit that outputs the select signal, the delay time control signal, and the cutoff control signal according to speed switching information that is given at the same time when the data transmission speed of the input signal is switched. Every time the switch signal is given, the select signal is given to the switch to switch the output of the switch to the other, and the cutoff frequency for band limitation corresponding to the data transmission rate is set for the LPF on the switched side. And a delay time control signal for setting a delay amount that does not affect the output data of the LPF on the separated side with respect to the delay circuit on the switched side. And multi-rate signal filter switching circuit.