JPS6224966B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comparison circuit used for reproducing data signals, and more particularly to a comparison circuit that compensates for deviations in comparison reference values due to the influence of low frequency components contained in data signals.

BACKGROUND ART Conventionally, in a data communication receiving system, when a comparison circuit reproduces a data signal, a DC component is removed by some method when comparing a reference voltage and a data signal voltage. A transient response element such as a capacitor is usually used to remove this DC component. Therefore, NRZ (Non
-Return to Zero) method, if the data signal continues to be at a high level, the data signal input to the comparator will drop to zero level due to the transient response of the capacitor, making comparison impossible and data reproduction impossible. . Conventionally, countermeasures for this problem include using a large-capacity capacitor to pass even low-frequency components in the data signal, or performing some kind of processing so that the data signal itself does not contain low-frequency components. These procedures do not allow sufficiently accurate reproduction of the data signal. It also has drawbacks such as a complicated structure of the device.

An object of the present invention is to provide a comparator circuit that eliminates these drawbacks.

According to the invention, a high-pass filter (hereinafter referred to as
HPF), a comparator that has a comparison signal input terminal and a reference voltage signal input terminal and compares the voltages of the input signals to these two terminals, and a limiter connected between the output of the HPF and the comparison signal input terminal. and feedback means inserted between the output of the comparator and the comparison signal or reference voltage signal input terminal.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic circuit diagram of a conventional comparison circuit for reproducing data signals, and FIGS. 2a and 2b are operation time charts thereof. When this comparison circuit is used in an FM receiver, when the signal electric field is input to the receiver,
Since the receiving center frequency of the receiver deviates by a certain frequency (Δ) with respect to the transmitting side frequency _p , a DC component corresponding to the frequency Δ is generated in the frequency discrimination circuit located before the comparison circuit. This DC component is added to the data signal. For example, the waveform becomes x _p in FIG. 2a. However, here in Figure 2, time t
This shows the case where a signal is received at _p . The input data signal x _p (voltage V _p ) that has passed through the HPF 1 consisting of the capacitor 10 (capacitance value C ₁ ) and the resistor 11 (resistance value R ₁ ) momentarily reaches the average voltage V _c of the data signal, but It gradually decreases and returns to zero level.
The time constant C ₁ R ₁ here has to be increased to some extent because it is necessary to remove the DC voltage V _c and at the same time pass the low frequency component of the data signal. As a result, the comparator 2 does not perform a correct comparison while the data signal returns to the zero level of the comparison reference value (section T _p in FIG. 2a). In addition, a section in which the data signal continues at a high level (section a in Figure 2)
At T ₁ ), the input signal to the comparator 2 falls to a low level like the signal x ₁ (voltage V ₁ ) in FIG. 2a, and correct data reproduction cannot be performed. The situation of erroneous data reproduction is shown in FIG. 2b.

FIG. 3 shows an embodiment of the comparator circuit according to the present invention, and FIGS. 4a and 4b are operation time charts thereof. Input data signal x ₆ with amplitude voltage V _D (voltage V ₆ )
are capacitor 12 (capacitance value C ₂ ), resistor 13
(resistance value R ₂ ), and the DC component is cut off. The output of the HPF 3 is limited by a limiter 4 (consisting of diodes X ₁ and X ₂ ) so that it does not exceed the forward voltage V _D of the diodes. The signal passing through the limiter 4 is compared with a comparison reference voltage (zero level) by a comparator 5. Comparator 5 outputs x 4 =+V _cc when x ₅ >0, and outputs x ₄ =+V cc when x ₅ <0.
Now, assume that x ₄ =-V _cc is output. Now, if the voltage of the output x ₄ is _Vcc , the output of the comparator at the voltage _Vcc is fed back to the non-inverting input terminal via the resistor 14 (resistance value R3 ₎ .

The response in this case is as follows.

Here, s=jω (ω is the angular frequency of the signal).

This shows the response characteristic of a first-order low-pass filter, and the time constant is C ₂ R ₂ R ₃ /(R ₂ +R ₃ ). however,
To facilitate calculation, the resistance value of the preceding stage circuit of the comparison circuit as seen from the input point of the comparison circuit was set to R ₀ 0.

Furthermore, the response of the voltage of the signal x ₅ due to the change in the voltage of the input signal x ₆ is as follows.

R ₂ R ₃ /(R ₂ +R ₃ )/1/sC ₂ +R ₂ R ₃ /(
R ₂ +R ₃ ) =sC ₂ R ₂ R ₃ /(R ₂ +R ₃ )/1+sC ₂ R ₂
R ₃ /(R ₂ +R ₃ ) This shows the response characteristic of a first-order high-pass filter, and the time constant is C ₂ R ₂ R ₃ /(R ₂ +R ₃ ).

Therefore, the time constant fed back from the comparator output to the non-inverting input terminal and the time constant due to the response between the input and output of the high-pass filter have the same value. That is, when the input signal x ₆ continues to be at a high level, as in section T ₁ of FIG _.
is equal to the increasing time constant of the voltage of the signal fed back through the resistor 14. This phenomenon is exactly the same when the signal remains constant in the negative direction; in this case, the feedback from signal x ₄ to signal x _{5 and the response of signal x 5 to} signal x ₆ have the same response characteristics. The voltage of the signal x ₅ reaches V ₅ =−V _cc R ₂ /(R ₂ +R ₃ ). Therefore, in both the positive direction and the negative direction of the signal, it is possible to prevent the voltage from dropping to zero level at the data signal input section of the comparator, which conventional comparison circuits have. Further, this comparator circuit cuts off the DC component Vc of the data signal by the diodes X ₁ and X ₂ of the limiter 4, thereby preventing erroneous comparison due to a transient response when the signal is input. For example, when a positive voltage V _c is applied to the signal, the diode X ₁ becomes conductive and the input voltage V ₅ of the comparator 5 does not rise above the voltage V _D. At this time, the resistance value when the diode is conductive and the capacitor 12
Since the time constant determined by the product of the capacitance values of is very small, the input voltage _V5 of the comparator 5 is rapidly pulled within the voltage _VD . When a negative voltage is applied to the signal, diode _X2 becomes conductive and the same result occurs.

FIG. 5 shows another embodiment of the comparison circuit according to the present invention, and FIGS. 6a and 6b are operation time charts thereof. Input signal x ₇ is capacitor 15 (capacitance etc.
C ₆ ), a HPF consisting of a resistor 16 (resistance value R ₆ ),
Circuit 6 with limiter consisting of diodes X ₃ and X ₄
The DC component V _c is cut off. The input signal _x8 of the comparator 7 is as shown in FIG. 6a. Up to this point, as in the conventional case, if the data signal continues to be at high or low level, the signal _x8 returns to zero level by the HPF. For this operation, the output of comparator 7 x ₉
is compensated by negative feedback to the inverting input terminal via a sign inverter 8 and a low-pass filter (LPF) 9 (consisting of a capacitor 17 and resistors 18 and 19). That is, as the HPF output x ₈ approaches the zero level, the comparison reference voltage of the feedback signal x ₁₀ responds transiently so as to maintain a constant potential difference with the HPF output x ₈ (see Figure 6 a). show). The limiter plays the same role as the circuit shown in FIG. 3 above.

In FIG. 5, the inverter 8 is removed and the comparator 7 is
It is clear that the same operation will occur even if the polarity of is reversed.

As explained above, according to the present invention, even if a data signal containing a DC component is input, erroneous comparison due to transient response does not occur, and even if the data signal is continuously at high or low level, erroneous comparison does not occur. Therefore, a comparator circuit that can reproduce correct data can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of a conventional comparison circuit, FIG. 2 is an operation time chart of the circuit in FIG. 1, FIG. 3 is an embodiment of a comparison circuit according to the present invention, and FIG.
FIG. 5 is an operation time chart of the circuit shown in FIG. 5, another embodiment of the comparison circuit according to the present invention, and FIG. 6 is an operation time chart of the circuit shown in FIG. In the figure, 1, 9... low pass filter, 2, 5, 7...
. . comparator, 3 . . . high pass filter, 4 . . . limiter, 6 . . . circuit including a high pass filter and limiter, 8 . . . sign inverter.

Claims (1)

[Scope of Claims] 1. A high-pass filter that receives an input signal in which a signal component is superimposed on a DC component and cuts out the DC component, a comparison signal input terminal and a reference voltage signal input terminal, and includes a comparison signal input terminal and a reference voltage signal input terminal. a comparator that compares the voltage signal with a voltage signal; and a second predetermined voltage that is connected between the output of the high-pass filter and the comparison signal input terminal and is lower than or equal to a first predetermined voltage and higher than the first predetermined voltage. A limiter that limits the voltage above the voltage,
positive feedback means inserted between the output of the comparator and the comparison signal input terminal, the transient response of the voltage obtained at the comparison signal input terminal when the input voltage of the high-pass filter changes; The response characteristics of the high-pass filter and the positive feedback means are adjusted so that when the voltage of the comparator output changes, the transient response of the voltage obtained through the positive feedback means and the comparison signal input terminal are equal. A comparison circuit characterized by the following settings. 2. The comparison circuit according to claim 1, wherein the positive feedback means is constituted by a resistor. 3. The comparison according to claim 1, wherein the comparison signal and reference signal input terminals of the comparator are non-inverting and inverting input terminals, respectively, and the positive feedback means is constituted by a low-pass filter. circuit. 4 A high-pass filter that receives an input signal in which a signal component is superimposed on a DC component and cuts out the DC component, and has a non-inverting input terminal and an inverting input terminal, and inputs the input signal to the non-inverting and inverting input terminals to a voltage. a comparator for comparison, and a second predetermined voltage, which is connected between the output of the high-pass filter and the non-inverting input terminal, and which is lower than or equal to a first predetermined voltage and higher than the first predetermined voltage.
a limiter that limits a voltage above a predetermined voltage; and negative feedback means inserted between the output of the comparator and the inverting input terminal; the high frequency range so that the transient response of the voltage obtained at the non-inverting input terminal is equal to the transient response of the voltage obtained at the inverting input terminal through the negative feedback means when the voltage of the comparator output changes; A comparison circuit characterized in that response characteristics of a pass filter and a negative feedback means are set. 5. The comparator circuit according to claim 4, wherein the negative feedback means comprises signal polarity inversion means and a low-pass filter. 6. The comparator circuit according to claim 1 or 4, wherein the limiter is constituted by a pair of diodes connected in parallel with opposite polarities.