JP3384744B2 - Coring circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coring circuit which does not generate an output signal for a low level input signal but generates an output signal for a high level input signal.

[0002]

2. Description of the Related Art A coring circuit using a noise canceller for removing minute noise in a signal is known. The coring circuit does not generate an output signal for a low level input signal but generates an output signal for a high level input signal.

As such a coring circuit, the circuit shown in FIG. 2 can be considered.

The input signal from the input terminal 100 of FIG.
It is applied to the first differential amplifier 101 and the second differential amplifier 102. First differential amplifier 101 and second differential amplifier 102
The output signals of 1 are combined and generated at the output terminal 103.

The first differential amplifier 101 is provided with a diode on the emitter side of each transistor, and its input dynamic range is set wide. The second differential amplifier 102 has no load on the emitter side of the transistor, and its input dynamic range is set narrow.

The current value of the operating current source of the first differential amplifier 101 is set sufficiently larger than the current value of the operating current source of the second differential amplifier 102.

Further, since the transistors 104 and 105 for inverting the phase are arranged in the second differential amplifier 102, the output signal of the second differential amplifier 102 has the opposite phase to the first phase.
It is added to the output signal of the differential amplifier 101.

As a result, when the second differential amplifier 102 is operating in the linear region, the output signal of the second differential amplifier 102 and the output signal of the first differential amplifier 101 are canceled and an output signal is generated. Will not do. This area is
It occurs when the input signal level is low.

When the level of the input signal increases, the influence of the output signal of the second differential amplifier 102 becomes negligible with respect to the output signal level of the first differential amplifier 101, which is proportional to the input signal. An output signal is generated at the output terminal 103.

[0010]

However, the circuit of FIG. 2 has a problem that a large number of elements and a current source are required.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and does not generate an output signal for a small level input signal, but does not generate an output signal for a large level input signal. A coring circuit for generating an output signal, a signal current source for generating an AC input signal, and a bias for supplying an output current of the signal current source to one end and applying a first reference voltage to the other end. A comparator for comparing the level of a resistance and an output terminal connected to the one end of the bias resistor with a voltage of the output terminal and a second reference voltage, and supplying an output current corresponding to the difference to the output terminal. It is characterized by having and.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The coring circuit of the present invention will be described with reference to FIG. In FIG. 1, 1 is a signal current source for generating an AC input signal, and 2 is an output current of the signal current source 1 supplied to one end and a first reference voltage from a first reference voltage source 3 is applied to the other end. Bias resistor 4 is an output terminal connected to the one end of the bias resistor 2, and 5 is an output terminal 4
Is compared with the first reference voltage from the first reference voltage source 3, and an output current corresponding to the difference is supplied to the output terminal 4.

Although the first reference voltage from the first reference voltage source 3 is applied to the comparator 5, another reference voltage having a different voltage in the vicinity of the first reference voltage may be applied. .

The output current of the signal current source 1 is an AC input current which is a target of coring. The AC input current flows through the bias resistor 2 to raise or lower the voltage at the output terminal 4. The DC voltage Vref is applied to the output terminal 4 from the first reference voltage source 3 via the bias resistor 2.

The voltage at the output terminal 4 changes with the product of the AC input current and the bias resistor 2 centered on the DC voltage Vref.

It is now assumed that the output current of the signal current source 1 is zero and there is no signal. Then, the voltage of the output terminal 4 becomes the voltage Vref. Output terminal 4 voltage Vref
Is applied to the base of the transistor 7 via the resistor 6. The transistor 7 constitutes the comparator 5. On the other hand, the base of the transistor 8 of the comparator 5 has a first
The DC voltage Vref from the reference voltage source 3 is applied. Therefore, the comparator 5 is in a balanced state,
The collector current of the transistor 9 and the collector current of the transistor 7 become equal. When these two currents are equal, no current flows from the point A to the resistor 6 or in the opposite direction.

That is, the comparator 5 does not affect the voltage of the output terminal 4.

Next, assume that the output current of the signal current source 1 is generated at a small level from this state. The small level is a so-called dead state level in which an output signal is not generated.

It is now assumed that a small level current flows from the signal current source 1 to the bias resistor 2. Then, the voltage of the output terminal 4 tries to rise. The voltage is applied to the base of the transistor 7 via the resistor 6. Then, the base voltage of the transistor 7 becomes higher than the base voltage of the transistor 8, and the collector current of the transistor 7 increases,
The collector current of the transistor 8 decreases. Since the transistor 9 constitutes a current mirror circuit, a current equal to the collector current of the transistor 8 flows through the collector of the transistor 9. Therefore, the transistor 7 draws the shortage current from the resistor 6.

As a result, even if the voltage of the output terminal 4 tries to rise, the voltage is limited by the action of the comparator 5 and does not rise.

Next, assume that a small level current flows from the bias resistor 2 to the signal current source 1. Then, the voltage of the output terminal 4 tends to decrease. The voltage is applied to the base of the transistor 7 via the resistor 6. Then, the base voltage of the transistor 7 becomes lower than the base voltage of the transistor 8, and the collector current of the transistor 8 increases,
The collector current of the transistor 7 decreases. Since the transistor 9 constitutes a current mirror circuit, a current equal to the collector current of the transistor 8 flows through the collector of the transistor 9. Therefore, the transistor 9 causes a current that cannot flow to the transistor 7 to flow through the resistor 6.

As a result, even if the voltage of the output terminal 4 is about to decrease, the voltage is limited by the function of the comparator 5 and does not decrease.

The function of limiting the voltage of the output terminal 4 is
It is limited by the current value of the operating current source 10 that constitutes the comparator 5. That is, the maximum current value flowing at the point A is determined by the current value of the operating current source 10, and determines the width of the dead zone.

Therefore, according to the circuit of FIG. 1, it is possible to prevent the output signal from being generated for the input signal of a small level.

Next, it is assumed that the output current of the signal current source 1 is generated at a large level. Then, in this case as well, the voltage of the output terminal 4 is generated depending on the direction and amount of the supplied input current. At the same time, the comparator 5 also operates. Since the input signal level is high, the comparator 5 operates immediately. However, if the current value of the operating current source 10 is made sufficiently smaller than the output current of the signal current source 1, the effect can be ignored.

As a result, according to the circuit of FIG. 1, there is obtained a coring circuit in which an output signal is not generated for a small level input signal and an output signal is generated for a large level input signal. .

[0027]

According to the present invention, it is possible to obtain a coring circuit in which an output signal is not generated for a low level input signal and an output signal is generated for a high level input signal.

Further, according to the present invention, it is possible to reduce the number of elements and the number of current sources.

[Brief description of drawings]

FIG. 1 is a diagram showing a coring circuit of the present invention.

FIG. 2 is a diagram showing a conventional coring circuit.

[Explanation of symbols]

1 Signal current source 2 Bias resistance 3 Reference voltage source 4 output terminals 5 comparator

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-2-36678 (JP, A) JP-A-3-1604 (JP, A) JP-A-6-315097 (JP, A) JP-A-58- 120311 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03G 11/00

Claims (2)

(57) [Claims] 1. A signal current for generating an AC input signal, which is a coring circuit that does not generate an output signal for a low level input signal and generates an output signal for a high level input signal. Source, an output current of the signal current source is supplied to one end and a first reference voltage is applied to the other end, an output terminal connected to the one end of the bias resistor, and a voltage of the output terminal And a second reference voltage for level comparison, and a comparator for supplying an output current corresponding to the difference to the output terminal. 2. A coring circuit that does not generate an output signal for a low level input signal and generates an output signal for a high level input signal, and a signal current that generates an AC input signal. Source, an output current of the signal current source is supplied to one end and a first reference voltage is applied to the other end, an output terminal connected to the one end of the bias resistor, and a voltage of the output terminal And a comparator for performing level comparison between the first reference voltage and the first reference voltage and supplying an output current corresponding to the difference to the output terminal.