JPS6150405B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a base clip circuit used to remove noise existing at a minute level or near zero level of a signal.

When there is noise in the AC signal near the zero level or at a minute level as shown in Figure 1A, as an example of a device that removes this noise, it is possible to remove noise in the vicinity of the zero level in the figure over a range of width W. A base clip circuit is used to suppress the noise.

FIG. 2 shows a conventional example of this base clip circuit.

That is, 1 and 2 are differentially configured transistors, the emitter of transistor 1 and the emitter of transistor 2 are commonly connected, and the connection point is grounded via the first constant current source 3. The collectors of these transistors 1 and 2 are connected to a power supply terminal 6 from which a positive DC voltage is obtained through resistors 4 and 5 having the same resistance value, respectively, and the collectors of these transistors 1 and 2 are connected in opposite directions to each other. first and second diodes 7,
8 series circuits are connected, and a connection point between these diodes 7 and 8 is grounded via a second constant current source 9. Then, connect terminal 1 to the base of transistor 1.
An input signal vi is supplied through the terminal 0, and a signal with the opposite phase of this signal vi is supplied to the base of the transistor 2 through the terminal 11.The first output terminal 12 is led out from the collector of the transistor 1, and from the collector of the transistor 2 A second output terminal 13 is led out.

In the conventional circuit shown in FIG. 2, the first and second
Let the currents of constant current sources 3 and 9 be I ₁ and I ₂ , the collector currents of transistors 1 and 2 be i ₁ and i ₂ , and input signal voltage vi=αI ₁ (|α|≦1/2), Since diodes 7 and 8 are conductive when there is no signal, a current of I ₂ /2 flows through these diodes 7 and 8, and a current of I ₁ /2 flows through each of transistors 1 and 2, so i ₁ = I ₁ + I ₂ /2 ... (1) i ₂ = I ₁ + I ₂ /2 ... (2) The output voltage V ₀ obtained as the potential difference between the output terminals 12 and 13 is the voltage difference between the resistors 4 and 5. If the value is R, then V ₀ =R (i ₁ −i ₂ )+K ₁ (K ₁ is a constant) (3), but this voltage v ₀ =0.

When the AC input signal current vi is supplied to the input terminals 10 and 11, the output voltage V ₀ changes depending on the magnitude of the input signal current vi.

When the input signal current vi is −i ₂ /2<vi<I ₂ /2, that is, in the range |αI ₁ |<I ₂ /2, this alternating current component is absorbed as a current component flowing through diodes 7 and 8. Therefore, it does not appear in the currents i ₁ and i ₂ , and in this range, i ₁ =
For i ₂ , if K ₁ = 0, then v ₀ = 0 (4).

Next, when vi=αI ₁ ≧I ₂ /2, the potential on the collector side of transistor 1 is lower than the reference potential at the connection point between the cathode of diode 7 and the cathode of diode 8, so diode 7 becomes non-conductive. , i ₁ =I ₁ /2+αI ₁ ...(5) On the other hand, since the diode (8) is conductive, i ₂ =I ₁ /2+I ₂ −αI ₁ ...(6). Therefore, the output voltage v ₀ is v ₀ =R(i ₁ −i ₂ )=2αI ₁ R−RI ₂ (7).

Moreover, when αI ₁ ≦I ₂ /2, conversely, the anode side potential is lower than the reference potential on the cathode side of diode 8, so this diode 8 becomes non-conductive, while diode 7 is conductive, so i ₁ = I ₁ /2 + αI ₁ + I ₂ ... (8) i ₂ = I ₁ /2 - αI ₁ ... (9) and the output voltage v ₀ is v ₀ = 2αI ₁ R + RI ₂ ... (10) Become.

From the above equations (4), (7) and (10), the input/output characteristics of this base clip circuit can be expressed as a broken line 14 in FIG. 3. Therefore, if the input signal vi is as shown in the figure, the output signal v ₀ is
It is as if the signal near zero of the input signal vi has been extracted with a width of I ₂ .

In this way, noise around zero in the input signal is removed, but in the case of the conventional circuit shown in FIG. 2, the output signal has a characteristic as shown by the broken line 14 in FIG. It becomes smaller by the amount that is cut out, which has the disadvantage that linearity deteriorates when the signal has a large amplitude.

The present invention seeks to provide a base clip circuit which allows the above-mentioned drawbacks to be easily eliminated.

Hereinafter, an embodiment of the base clip circuit according to the present invention will be described with reference to the drawings.

That is, in this invention, as shown in FIG. 4, a series circuit of two resistors 15 and 16 replaces the resistor 4 of the circuit of FIG. are connected respectively, and the connection point of these resistors 15 and 16 and the resistor 1
A third diode 1 is connected between the connection points 7 and 18.
9 is connected, and a fourth diode 20 is connected in parallel with this diode 19 in the opposite direction.

In this case, resistors 15 and 17 and resistors 16 and 1
8, those having the same characteristics and the same resistance value are used. The rest of the circuit is the same as the circuit shown in FIG.

The operation of this circuit will be explained below.

First, the input signal vi is small, |αI ₁ |<I ₂ /2
In the range of , the diode 7
and 8 are conductive, so the output voltage v ₀ is v ₀ =0 (11).

Furthermore, if we do not consider the effects of diodes 19 and 20, and considering that the load resistance is a series circuit of resistors 15 and 16 and a series circuit of resistors 17 and 18 instead of resistors 4 and 5, the above ｜αI ₁
Even outside the range of <I ₂ /2, it is the same as the example in Figure 2, and the resistance 1
If the value of resistors 16 and 18 is R ₁ and the value of resistors 16 and 18 is R ₂ , when αI ₁ ≧I ₂ /2, diode 7 becomes non-conducting and diode 8 becomes conductive, and the output voltage v ₀
is _v0 =( _i1 − _i2 )( _R1 + _R2 )= _2αI1 ( _R1 + _R2 ) _−I2 ( _R1 + _R2 )...(12).

Furthermore, when αI ₁ ≦-I ₂ /2, diode 7 becomes conductive and diode 8 becomes non-conductive, so the output voltage
v ₀ is v ₀ =2αI ₁ (R ₁ +R ₂ )+I ₂ (R ₁ +R ₂ )...(13).

However, when the diodes 19 and 20 of this example exist, when αI ₁ becomes larger than the predetermined value in the range of αI ₁ ≧I ₂ /2, αI ₁ ≦−I ₂ /2,
and when it becomes smaller than a predetermined value, a situation different from that in FIG. 2 occurs.

Hereinafter, to explain this, in order to simplify the explanation, we will first consider the case where the constant current source 9 has no effect.

Now, the voltage when the diodes 19 and 20 are conductive is V
_D , when I ₂ /2≦αI ₂ ≦V _D /2R ₂ ,
Since a voltage exceeding the voltage V _D is not applied across the diodes 19 and 20, both diodes 19 and 20 are non-conductive, and the output voltage v ₀ is i ₁ =I ₁ /2+αI ₁ ...(14) Since i ₂ = I ₁ /2 − αI ₁ ...(15), v ₀ = (R ₁ + R ₂ ) (i ₁ − i ₂ ) = 2αI ₁ (R ₁ + R ₂ ) ...(16) Become. Further, when αI ₁ >V _D /2R ₂ , the cathode side of the diode 19 becomes lower than the anode side by more than V _D , so this diode 19 becomes conductive and the diode 20 becomes non-conductive, and the output voltage v ₀ becomes v ₀ =R ₁ (i ₁ −i ₂ )+V _D 2αI ₁ R ₁ +V _D (17).

Here, if we add the effect of the constant current source 9, we get 16
Equation 17 can be rewritten as follows in the same way as equation 12.

v ₀ =2αI ₁ (R ₁ +R ₂ )−I ₂ (R ₁ +R ₂ ) ……(16′) v ₀ =2αI ₁ R ₁ +V _D −I ₂ (R ₁ +R ₂ ) ……(17′) Similarly, −I ₂ /2≧αI ₁ ≧−V _D /2R
₂ , both diodes 19 and 20 are non-conductive, so v ₀ =2αI ₁ (R ₁ +R ₂ )+I ₂ (R ₁ +R ₂ )...(18), and αI ₁ <-V _D / When 2R ₂ , diode 2
Since the anode side of 0 is higher than the cathode side by more than V _D , diode 19 is non-conducting and diode 2
Since 0 is conductive, v ₀ =2αI ₁ R ₁ −V _D +I ₂ (R ₁ +R ₂ ) (19).

If it is determined that V _D =I ₂ (R ₁ +R ₂ ), both equations (17') and (19) become as follows.

v ₀ =2αI ₁ R ₁ ...(20) If we put the above in order, when |αI ₁ |<I ₂ /2, v ₀ =0 ...(21) I ₁ /2≦αI ₁ ≦V _D /2R ₂ and -I ₂ /2≧αI ₁
When ≧−V _D /2R ₂ , v ₀ =2αI ₁ (R ₁ +R ₂ )−I ₂ (R ₁ +R ₂ )……(22) αI ₁ >V _D /2R ₂ and αI ₁ <−V When _D /2R ₂ , v ₀ =2αI ₁ R ₁ ...(23). If this is represented in a diagram, it will be as shown by the broken line 21 in FIG.

That is, according to the present invention, noise near zero level in the input signal is removed, and output characteristics with good linearity are obtained for large amplitude signals.

Therefore, unlike the conventional example, the output signal does not become small in response to a large amplitude input signal.

FIG. 6 shows an example of a practical circuit of the base clip circuit according to the present invention, where 22 is an input terminal and 23 is an output terminal. Further, 24 is a resistor serving as the constant current source 3, 25 is a variable resistor for balance adjustment, and 26 is a transistor constituting the constant current source 9. In this example, the output signal is such that the collector output of transistor 2 is the emitter follower transistor 27.
It is made to be taken out through.

As described above, according to the present invention, the drawbacks of the conventional circuit can be easily eliminated by cleverly providing two diodes in the conventional circuit.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the base clip circuit, Figure 2 is a diagram showing the principle of the conventional circuit, Figure 3 is a diagram for explaining it, and Figure 4 is the diagram of the principle of the circuit of this invention. 5 is an output characteristic diagram for explaining the same, and FIG. 6 is a circuit diagram showing an example of a practical circuit of the circuit of the present invention. 1 and 2 are first and second transistors, 3 is a first constant current source, 6 is a power supply terminal, 7 and 8 are first
and a second diode, 9 is a second constant current source, 1
0 and 11 are input terminals, 12 and 13 are output terminals, 1
5 and 16 are the first and second resistors, 17 and 18
are first and second resistors, and 19 and 20 are first and second diodes.

Claims (1)

[Scope of Claims] 1. A connection point between the emitters of the first and second transistors configured differentially is grounded via a first constant current source, and a connection point between the collector of the first transistor and the power supply terminal is grounded via a first constant current source. is connected to a series circuit of first and second resistors, a series circuit of third and fourth resistors is connected between the collector of the second transistor and the power supply terminal, and a series circuit of third and fourth resistors is connected between the collector of the second transistor and the power supply terminal. A series circuit of first and second diodes connected in opposite directions is connected between the connection point of the first resistor and the connection point of the second transistor and the third resistor. A connection point of the second diode is grounded via a second constant current source, and a connection point of the first and second resistors and a connection point of the third and fourth resistors are connected to each other in opposite directions. A parallel circuit of third and fourth diodes is connected, the values of the first and third resistors are both R ₁ , the values of the second and fourth resistors are both R ₂ , and when the diodes are conductive, When the voltage of the transistor is V _D and the current of the second constant current source is I ₂ , the following relationship is established: V _D = I ₂ (R ₁ + R ₂ ), and the first and second transistors A base clip circuit, wherein input signals having mutually opposite phases are supplied to the bases of the transistors, and an output signal can be taken out from the collectors of the first or second transistors.