JPH0511706B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a waveform shaping circuit for a serial packet signal that is subject to a frequency band restriction of a transmission path, such as a digital signal included in a received signal of teletext broadcasting. Regarding.

[Conventional technology]

Conventionally, this type of waveform shaping circuit, as shown in FIG. a second buffer amplifier 5 with a high input impedance to which the input signal is input, a switch circuit 4 which is turned on at the burst phase of the serial packet signal and which connects the input of the second buffer amplifier 5 directly to the ground;
The comparator circuit 7 receives the output from the buffer amplifier 5 and outputs a signal whose waveform has been shaped based on the reference voltage 6.

When a serial packet signal that has been band-limited is converted back into a digital binary serial packet signal on the receiving side in order to pass through a transmission path, in Fig. 4, the band-limited serial packet signal 1 is It is converted to a low impedance by a buffer amplifier 2, and then passed through a capacitor 3 and inputted to a buffer amplifier 5 having a high input impedance. At this time, the pedestal portion of the serial packet signal is clamped to the ground potential by turning on the switch circuit 4 only in the burst phase of the serial packet signal as shown in Fig. 5a and b, and then the high input impedance is The output of the buffer amplifier 5 is input to a comparator circuit 7.

On the other hand, as shown in FIG. 5a, by setting the reference voltage 6 of the comparator circuit 7 to a potential that is half the amplitude of the serial packet signal,
The band-limited serial packet signal is shown in Figure 5c.
As shown in the figure, a shaped output 8 was obtained by converting it into a digital binary serial packet signal.

[Problem that the invention seeks to solve]

In the conventional waveform shaping circuit described above, when the serial packet signal is at the normal level, it is correctly shaped, but when it fluctuates from the normal level, for example, when the level of the serial packet signal becomes less than half, the shaped output 8 There was a problem that the image would disappear and not be formatted correctly.

The present invention solves the above problems and provides a waveform shaping circuit that can always perform normal waveform shaping regardless of level fluctuations in the serial signal.

[Means for solving problems]

In order to achieve the above object, a waveform shaping circuit according to the present invention includes a first buffer amplifier, a second buffer amplifier, a switch circuit, and a comparator circuit. The amplifier receives a band-limited serial packet signal as input, converts it to low impedance, and outputs it to a second buffer amplifier. The second buffer amplifier is set to high impedance, and the first buffer The DC component of the output of the amplifier is input and output to the comparator circuit.The switch circuit has a resistor and turns on only the clock line portion of the serial packet signal, passing it through the resistor to the input of the second buffer amplifier. The resistor prevents the amplitude of the clock line component of the output of the first buffer amplifier from disappearing when the switch circuit is on, and also prevents the clamp potential from losing the amplitude of the clock line component of the output of the first buffer amplifier when the switch circuit is on. The comparator circuit inputs the output of the second buffer amplifier and the reference voltage, and outputs a signal whose waveform is shaped based on the reference voltage.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, this embodiment consists of a first buffer amplifier 1, a capacitor 3, a second high input impedance buffer amplifier 5, a switch circuit 4 grounded through a resistor 9, and a comparator circuit 7. Become. 1 is a serial packet signal whose band is limited in order to prevent waveform distortion caused by the transmission path. The buffer amplifier 2 to which this serial packet signal 1 is input has a low output impedance to prevent the waveform from being distorted when the next stage switch circuit 4 is turned on. capacitor 3
generates a DC component at the key ink clamp. The switch circuit 4 is turned on only at the clock run portion of the serial packet signal, as shown in Figure 2 a and b.
and ground through resistor 9. resistance 9
prevents the amplitude of the clock run component of the buffer output of the buffer amplifier 2 from disappearing when the switch circuit 4 is ON, and also prevents the clamp potential from being influenced by the timing when the switch circuit 4 turns OFF. The second buffer amplifier 5 is a capacitor 3
It has a high input impedance to maintain the clamp potential held at . The comparator circuit 7 compares the output of the buffer amplifier 5 based on the reference voltage (GND), performs the comparison using the center potential of the serial packet signal as a reference, and obtains a waveform-shaped output 8 as shown in Figure 2c. .

In the embodiment, as shown in FIG. 2, the clock run section of the serial packet signal has data "1",
It is a series of "0"s, and the DC component is the center potential of the amplitude of the serial packet signal. Therefore, by turning ON the switch circuit 4 only at the clock run portion of the serial packet signal 1, the center of the serial packet signal is always clamped to the ground potential. On the other hand, by setting the reference potential 6 of the comparator circuit 7 to the ground potential, waveform shaping is performed by slicing the center of the amplitude of the serial packet signal as shown in FIGS. 3a and 3b. Even if the level of the packet signal after clamping fluctuates within the range of ±6 dB from the normal level, the waveform will always be correct because the serial packet signal is always sliced at the center of its amplitude as shown in Figure 3 a and b. Plastic surgery can be performed.

〔Effect of the invention〕

As explained above, the present invention changes the clamp phase of the serial packet signal from the burst signal part to the clock run part, and at the same time uses this clamp potential as a reference potential and shapes the clamp output with a comparator circuit, thereby increasing the amplitude of the serial packet signal. This has the effect of correctly shaping the waveform even when it fluctuates from the normal level.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figures 2a, b, and c are waveform diagrams of various parts, Figures 3a and b are waveform shaping output diagrams when the level of the serial packet signal changes, Figure 4 is a block diagram of the conventional example, and Figures 5a and b. , c are waveform diagrams of various parts in the conventional example. 1, 5... Buffer amplifier, 3... Capacitor, 4... Switch circuit, 7... Comparator circuit.

Claims (1)

[Scope of Claims] 1. A waveform shaping circuit including a first buffer amplifier, a second buffer amplifier, a switch circuit, and a comparator circuit, wherein the first buffer amplifier is a band-limited serial packet. The second buffer amplifier is set to high impedance and receives the DC component of the output of the first buffer amplifier as input. The switch circuit has a resistor, turns on only the clock line portion of the serial packet signal, and connects the input side of the second buffer amplifier to ground through the resistor. The resistor prevents the amplitude of the clock line component of the output of the first buffer amplifier from disappearing when the switch circuit is on, and also prevents the clamp potential from being influenced by the timing when the switch circuit is off. A waveform shaping circuit, characterized in that the comparator circuit inputs the output of the second buffer amplifier and the reference voltage, and outputs a signal whose waveform is shaped based on the reference voltage.