JPS6253967B2 - - Google Patents

Description

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

Generally, in a data signal transmission/reception system, a transformer, a coupling capacitor, etc. are inserted in the transmission path, so it is difficult to faithfully transmit the DC component or low frequency component of the data signal. On the other hand, on the receiving side of this type of transmission system,
The average voltage of the data signal obtained by the low-pass filter is used as the determination threshold (hereinafter referred to as comparison reference value) of the comparator for determining whether the data signal is "1" or "0". For this reason, for example, when "1" continues as a data signal, the comparison reference value may deviate, resulting in an erroneous determination.

Conventionally, to avoid this, it was necessary to increase the capacitance of the low-pass filter capacitor to pass as many low frequency components as possible, or to use a signal pattern that removed low frequency components by processing the data signal itself. It was hot.

An object of the present invention is to provide a comparison circuit that eliminates deviations in comparison reference values due to fluctuations in low frequency components contained in received data signals.

According to the present invention, a comparator has a non-inverting input terminal and an inverting input terminal and compares voltages of input signals to the non-inverting and inverting input terminals, and a signal input terminal connected to the non-inverting input terminal; A comparison circuit is obtained that includes a low-pass filter connected between the signal input terminal and the inverting input terminal, and negative feedback means inserted between the output of the comparator and the inverting 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.
Figures 2a and 2b are operation time charts.
For example, in the case of an FM receiver, when a signal electric field is input, the receiving center frequency of the receiver deviates by a certain value Δ from the center frequency _p of the transmitting side.
At the output of the frequency discrimination circuit, a DC voltage corresponding to Δ is generated, and the DC voltage is added to the signal. In such a case, in the conventional circuit shown in Fig. 1, capacitor 18 (capacitance value C ₁ ), resistor 19 (resistance value
A low-pass filter 1 consisting of R ₁ brings the comparison reference value V ₁ close to the average voltage V _c of the signal. If the time constant R ₁ C ₁ of the filter 1 is increased here, the time for the comparison reference value x ₁ to approach the average voltage V _c of the signal is delayed, and it takes time for the comparison circuit 2 to perform a normal comparison. Conversely, if the time constant R ₁ C ₁ is made smaller, when the signal continues to have a high level as shown in section T ₁ in Figure 2a, the comparison reference value x ₁ indicates that circuit 1 is a low-pass filter. Therefore, it approaches the high level of the input signal. This means that the signal x ₀ (voltage
This can also cause erroneous comparisons due to noise contained in V ₀ ). As described above, conventional circuits have the disadvantage that they cannot use signal patterns in which high or low levels continue for long periods of time.

FIG. 3 shows an embodiment of the present invention. Figure 4 a~
c is the operation time chart. In Fig. 3, the comparison reference value V ₃ is the input x ₆ (voltage V ₆ ), the capacitor 20 (capacitance value C ₂ ), and the resistor 21 (resistance value R ₂ ).
The output x ₅ (voltage V ₅ ) of the inverter 5 is passed through a low-pass filter 3 consisting of a resistor 22 (resistance value
R ₃ ). That is, after the signal is received and a steady state is reached, the reference reference value
V ₃ becomes (V ₆ P ₃ +V ₅ R ₂ )/(R ₂ +R ₃ ). Here, as shown in FIG. 4a, the ideal comparison reference value is V _c ,
Let the amplitude of the data signal be _Vs. Suppose now that the signal continues to be at a high level for some time, as shown in section _T1 in FIG. 4a. In this case, the input signal
Since the voltage V ₆ of x ₆ is V _c +V _s , the reference value V ₃ is {V _c
R ₃ / (R ₂ + R ₃ )} + {(V _s R ₃ + V ₅ R ₂ ) / (R ₂ +
R ₃ )}. Here, R ₂ ≪ R ₃ , V ₅ = −V _s R ₃ /R ₂
If V ₃ V _c is selected, the reference value V ₃ will not deviate from the ideal comparison value V _c even if high level signals continue. The above is a case where the signal continues to be at a high level, but the same applies to a case where the signal continues to be at a low level.

Next, the transient response will be explained. The transfer function from input signal x ₆ to signal x ₃ is as follows.

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

Similarly, the transfer function from output signal x ₅ to signal x ₃ is as follows.

In other words, both exhibit the response characteristics of a first-order low-pass filter and have the same time constant C ₂ R ₂ R ₃ /(R ₂ +R ₃ ). In other words, in the case of the circuit shown in Figure 3, the time constant for charging from the input signal x ₆ to the signal x ₃ is equal to the time constant for discharging from the output signal x ₅ to the signal x ₃ , so the circuit shown in Figure 4 a This means that V ₃ V _c also holds true for the initial transient state of interval T ₁ .

As explained above, after a certain period of time has passed after receiving a signal, the comparison reference value x ₃ can maintain the ideal comparison reference value even if the input signal continues to be at a high or low level, so the time constant R ₂ C ₂ can be chosen small. This also means that the time required for the reference value x ₃ to reach the ideal comparison reference value V _c at the beginning of signal reception also becomes faster.

FIG. 5 shows a second embodiment of the invention. The input signal x ₇ (voltage V ₇ ) is passed through the low-pass filter 9 (amplifier 1
2. It is composed of resistors 24 and 25 (resistance values R ₄ and R ₅ ) and a capacitor 23 (capacitance value C ₄ ). ). In addition, the output of the comparator 8 is passed through a low-pass filter 10 (amplifier 11, resistor 27 to
29 (resistance values R ₆ to R ₈ ) and a capacitor 26 (capacitance value C ₃ ). ). The comparison reference value V ₉ is a combination of the respective output voltages of the low-pass filters 9 and 10 . Therefore,
The respective outputs of amplifiers 11 and 12 in FIG.
For the voltages V ₁₁ and V ₁₂ of x ₁₁ and x ₁₂ , the reference value V ₉ is V ₉ =
It is expressed as (V ₁₁ R ₅ +V ₁₂ R ₆ )/(R ₅ +R ₆ ). Therefore, when a constant voltage continues as in section T ₁ in Figure 4a, when a steady state is reached, V ₁₂ = V _c + V _s holds, so the reference value V ₉ at this time is V ₉ = { V _c
R ₆ / (R ₅ + R ₆ )} + {(V ₁₁ R ₅ + V _s R ₆ ) / (R ₅ +
R ₆ )}. Therefore, resistors R ₅ and R ₆ and voltage V ₁₁ are selected so that V ₁₁ = −V _s R ₆ /R ₅ is established, and R ₅
If <<R ₆ , then V ₉ V _c holds true and it is possible to maintain the ideal comparison value in a steady state.

Next, the transient response will be explained. The response of the voltage V ₁₂ of x ₁₂ when the voltage V ₇ of input signal x ₇ changes is: It is expressed as , and the time constant is C ₄ R ₄ .

Next, when the voltage V ₈ of the output signal x ₈ changes
The response of _the voltage V _{11 of} x ₁₁ is - Feedback impedance _of amplifier 11 /
1/ _sC3 / _R7 +1/ _sC3 }= _R7 / _R8-1 /1+ _sC3R7 , and _{the time constant is C3R7 .}

If V ₉ V _c holds in steady state, both time constants
If C ₄ R ₄ and C ₃ R ₇ are equal, the voltage of _the signal It is possible to maintain the ideal comparison value even in a transient state of the signal. Even in this case, the time constant R ₄ C ₄ can be selected to be small, so that the comparison reference value V ₉ can quickly reach the ideal comparison value at the beginning of signal reception.

FIG. 6 shows a third embodiment of the present invention, in which diodes D ₁ and D ₂ are further added to FIG. 3.
The saturation voltage of the diodes D ₁ and D ₂ is chosen to be only slightly higher than the amplitude voltage V _s of the input signal. In this case, after a while after receiving the signal, the characteristics are similar to those in the case shown in FIG. ₃ of the present invention, but at the beginning of signal reception, the _amplitude of the input signal When this occurs, either diode D ₁ or D ₂ becomes conductive. Therefore, the voltage V ₁₅ of the comparison reference signal x ₁₅ can reach the ideal reference comparison value V _c in a very short time. In addition,
In FIGS. 3 and 6, comparators 4 and 1
If the polarity of 6 is reversed, inverters 5 and 1
7 becomes unnecessary.

As explained above, by using the comparison circuit of the present invention, it is possible to compare signals with continuous high or low levels as a signal pattern using an ideal reference value, and also to receive signals with a DC level added to them at the same time. In some cases, the ideal comparison state is reached quickly.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of a conventional comparison circuit, FIGS. 2a and 2b are operation time charts of the comparison circuit in FIG. 1, FIG. 3 is a first embodiment of the present invention, and FIGS.
c is an operation time chart of the circuit in FIG. 3, FIG. 5 is a second embodiment of the present invention, and FIG. 6 is a third embodiment of the present invention.
FIGS. 7a to 7c are operation time charts of the circuit in FIG.
0,15...Low pass filter, 2,4,8,1
1, 12, 16...comparators, 5, 17...inverters.

Claims (1)

[Scope of Claims] 1. A comparator that has a non-inverting input terminal and an inverting input terminal and compares voltages between the non-inverting and inverting input terminals, and a comparator that receives an input signal in which the signal component is heavy on the DC component, and a signal input terminal connected to the non-inverting input terminal; and a first low voltage terminal connected between the signal input terminal and the inverting input terminal and having a sufficiently large time constant compared to the time at which the signal component changes. a pass filter, and negative feedback means inserted between the output of the comparator and the inverting input terminal, the input voltage to the inverting input terminal being the center voltage of the signal component in a steady state, and The transient response of the voltage obtained at the inverting input terminal through the first low-pass filter when the voltage at the signal input terminal changes, and the voltage transient response obtained at the inverting input terminal through the first low-pass filter when the voltage at the comparator output changes, A comparison circuit characterized in that the response characteristics of the first low-pass filter and the negative feedback means are set so that the transient response of the voltage obtained at the inverting input terminal is equal. 2. The comparison circuit according to claim 1, wherein the negative feedback means is comprised of a signal polarity inversion means and a resistor. 3. The comparison circuit according to claim 1, wherein the negative feedback means is constituted by a second low-pass filter. 4. The comparison circuit according to claim 1, wherein the first low-pass filter is composed of a capacitor and a resistor. 5. Claim 5, characterized in that the first low-pass filter is constituted by a capacitor, a resistor, and a pair of diodes connected to the resistor in parallel and with opposite polarities. Comparison circuit described in item 1.