JPS6359196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a differentiating circuit used in, for example, a WDD (Winch-Ester Disk Drive) and an FFD (Floppy Disk Drive).

[Technical background of the invention and its problems]

Conventionally, this type of differential circuit has been configured as shown in FIG. 4, for example. In Figure 4, Q
1 and Q2 are NPN type differential input transistors,
Base side terminal 1 of these transistors Q1 and Q2
An AC power supply Vi is connected to 1 ₁ and 11 ₂ . Terminal 12 on the emitter side of the above transistors Q1 and Q2
A capacitor C is externally connected between ₁ and ₁₂₂ . Further, constant current sources I1 and I2 are connected between the emitters of the transistors Q1 and Q2 and the ground point, respectively. Resistors R1 and R are connected between the collectors of the transistors Q1 and Q2 and the positive constant voltage source _VDD .
2 are connected, and differential output is generated from output terminals 13 ₁ and 13 ₂ on the collector side of these transistors Q1 and Q2.
Get V _O.

In the above configuration, the capacitor C provided between the emitters of the differential input transistors Q1 and Q2 performs a differential operation, and the current flowing between the collectors and emitters of the transistors Q1 and Q2 flows through the resistors R1 and It is converted into a voltage by R2, and a differential output V _O is obtained from the output terminals 13 ₁ and 13 ₂ .

Now, if the resistance values of resistors R1 and R2 are R _L and the capacitance of capacitor C is C _D , then the above differential output
V _O can be expressed by the following equation (1).

V _O =2R _L・C _D dVi/dt (1) By the way, in the differentiating circuit used in the WDD and FDD, the output terminals 13 ₁ and 13 ₂ are connected to the input terminal of the comparator 14, respectively, An output signal OUT is obtained from this comparator 14.

However, when the output of the differentiator is directly connected to the input of the comparator in this way, the DC offset voltage caused by the ratio of the resistors and the ratio of the constant current source is directly transmitted to the comparator, resulting in poor symmetry of the output of the comparator. There is a drawback.

[Purpose of the invention]

This invention was made in view of the above circumstances, and its purpose is to improve the symmetry of the comparator output by preventing DC offset voltage from appearing in the output, thereby achieving highly accurate output. The object of the present invention is to provide an excellent differential circuit that can obtain the following.

[Summary of the invention]

That is, in this invention, in order to achieve the above object, as the output load of the differential amplifier,
An inductive load using an inductor is used instead of a resistive load, and since the inductor has a resistance of 0Ω in terms of direct current, no direct current offset voltage appears.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same components as those in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted. That is, the differential input transistor Q
A resistor R3 is connected between the emitters of the transistors Q1 and Q2, and inductors L1 and L2 are connected between the collectors of the transistors Q1 and Q2 and the constant voltage source _VDD , respectively.

In the above configuration, when a differential input signal is supplied from the AC power supply Vi to the bases of the differential input transistors Q1 and Q2, one transistor is turned on and the other transistor is turned off. Now, assuming that the transistor Q1 is on and the transistor Q2 is off, a current flows from the constant voltage source V _DD through the inductor L1 between the collector and emitter of the transistor Q1. At this time, the inductor L1 differentiates the current flowing between the collector and emitter of the transistor Q1. The emitter current of the transistor Q1 is the constant current source I
1 to the ground point, and the resistor R
3 and a constant current source I2 to the ground point. The resistor R3 functions to widen the range and linear region of the differential input voltage. Then, the amount of change in the current differentiated by the inductor L1 is outputted to the output terminals 13 ₁ , 13 ₂ as the differential output V _O.
obtained from between. Note that the same operation is performed when the transistor Q2 is in the on state and the transistor Q1 is in the off state.

When the inductances of the inductors L1 and L2 are respectively L _D , the differential output V _O is expressed by the following equation (2).

V _O =2L _D・di/dt (2) Here, since the current i is Vi/R ₃ , V _O =2LLD・1/R ₃・dVi/dt (3). Equation (3) above indicates that the differential input signal Vi is differentiated to obtain an output voltage V _O.

According to such a configuration, the inductors L1, L
Since the impedance of No. 2 is 0Ω in terms of DC, no DC offset voltage appears. Therefore,
The symmetry of the output of the comparator 14 can be improved, and highly accurate output can be obtained.

FIG. 2 shows another embodiment of the present invention, in which resistors R4 and R5 are connected in series between the emitters of differential input transistors Q1 and Q2, and these resistors R
A constant current source I3 is provided between the connection point of 4 and R5 and the ground point.

Even in this configuration, basically the same operation as the circuit shown in FIG. 1 described above is performed and the same effects can be obtained.

FIG. 3 shows yet another embodiment of the invention, in which an emitter follower is added to the circuit of FIG. 1 in order to set the input resistance high. That is, the emitters of transistors Q3 and Q4 are connected to the bases of transistors Q1 and Q2, respectively.
The bases of No. 4 are connected to terminals 11 ₁ and 11 ₂ , respectively. Further, the collectors of the transistors Q3 and Q4 are respectively connected to a constant voltage source _VDD , and constant current sources I4 and I5 are connected between each emitter and a ground point.

According to such a configuration, the transistors Q3,
The input resistance can be increased by Q4, and the range of application of the circuit can be expanded. Of course, in this circuit, no DC offset voltage appears in the output.

〔Effect of the invention〕

As explained above, according to the present invention, by preventing the appearance of DC offset voltage in the output, it is possible to improve the symmetry of the output of the comparator and provide an excellent differentiating circuit that can provide highly accurate output.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a differentiating circuit according to an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing other embodiments of the present invention, and FIG. 4 is a diagram showing the configuration of a conventional differentiating circuit. FIG. Q1, Q2...Differential input transistor, Vi...
...AC power supply (differential input signal), R3 to R5...Resistor, I1 to I5...Constant current source, V _DD ...Constant voltage source, L1, L2...Inductor (inductive load),
V _O ... Differential output.

Claims (1)

[Claims] 1 A pair of differential input transistors whose bases are supplied with differential input signals, a resistor provided between the emitters of these differential input transistors, and a resistor provided between the emitters of the differential input transistors and a ground point. a constant current source, and first and second inductive loads respectively provided between each collector of the differential input transistor and the constant voltage source,
A differentiation circuit characterized in that a differential output of the differential input signal is obtained from each collector of the differential input transistor.