JPH0314277A - Dc level difference compensation circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit enabling DC level difference between a plurality of signals to be compensation easily by providing specific DC signal output means, DC level difference calculation means, and DC level compensation means. CONSTITUTION:The tittle item has a plurality of DC signal output means which output the same level DC signal as each DC level Va and Vb of a plurality of signal Vi1 and Vi2, a DC level difference calculation means A3 which performs subtraction between a reference DC level reference signal E1 and the above each DC signal and then output DC level difference signal Ve, and a DC level compensation calculation means A4 which performs subtraction between each of the above plurality of signals Vi1 and Vi2 and the above DC level difference signal Ve corresponding to them and compensates each DC level Va and Va of the above plurality of signals Vi1 and Vi2. For example, it is connected to a bi-phase differential magnetic sensor. A preamplifier 1 consists of a DC level difference calculation means using the operational amplifier A3 and a DC level compensation calculation means using the operational amplifier A4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC level difference correction circuit between a plurality of signals, and is particularly useful for a preamplifier of a low reencoder of two or more phases.

[Conventional technology] FIG. 2 is a schematic diagram of a two-phase low reencoder.

G is a detection gear made of a magnetic material, S is a two-phase differential magnetic sensor, and a magnet m is installed at the bottom thereof.

FIG. 3 shows the structure of the two-phase differential magnetic sensor S, which includes four magnetoresistive elements Mal, Mb1Ma2 .
Mb2 are arranged at a predetermined pitch, a voltage EO is applied to a series circuit of magnetoresistive elements Mal and Ma2, and a signal voltage Vil is derived from the midpoint. The signal voltage Vil is
It consists of a change amount Wa that fluctuates with the rotation of the detection gear G and a direct current component Va that is unrelated to the rotation of the detection gear G. Also,
Power supply voltage EO is applied to the series circuit of magnetoresistive elements Mbl and Mb2.
is added, and the signal voltage Vi2 is derived from the midpoint. The signal voltage Vi2 includes a variation wb that fluctuates due to the rotation of the detection gear G and a DC component v that is unrelated to the rotation of the detection gear G.
It consists of b.

FIG. 4 shows a conventional preamplifier circuit 51 and a comparator C1 connected to the two-phase differential magnetic sensor S described in "1".

The signal voltage Vil is input to the negative input terminal of the operational amplifier A1 via the resistor R1.

The negative input terminal of the operational amplifier Δ1 is connected to the output terminal via the resistor R2, and the positive input terminal is connected to the signal voltage Vi.
A DC voltage matched with the DC component Va of l is input. Therefore, the output voltage VOI of the operational amplifier A1 becomes VO1=Wa-R2/R1+Va, as shown by the solid line in FIG. 5(a), for example.

The same holds true for the other signal voltage Vi2, and the output voltage VO2 of the operational amplifier A2 is as follows: VO2=Wb-R2/R1+Vb, as shown by the dotted line in FIG. 5(a).

These output voltages VOI and VO2 are input to a comparator C1, and the comparator C1 outputs a pulse signal Pa as shown in FIG. 5(b).

The rotational position can be detected based on the pulse number and phase of this pulse signal Pa.

[Problems to be Solved by the Invention] As understood from FIGS. 5(a) and (b), the output signal V
The phase of the pulse signal Pa fluctuates due to variations in the DC components Va and Vb of OI and VO2.

Therefore, magnetoresistive elements Mal to Mb2 having similar resistance values are selected and used so that the direct current components Va and vb match as much as possible.

However, sorting out the magnetoresistive elements Mal to Mb2 in this way is complicated, and there is a problem in that the yield is reduced.

Therefore, an object of the present invention is to provide a DC level difference correction circuit that can easily correct even if there is a difference in DC level between a plurality of signals.

[Means for Solving the Problems] The DC level difference correction circuit of the present invention includes a plurality of DC signal output means for outputting DC signals of the same level as each DC level of a plurality of signals, and a reference signal of a reference DC level. DC level difference calculation means that performs subtraction between each of the DC signals and outputs a DC level difference signal; and DC level difference calculation means that performs subtraction between each of the plurality of signals and the DC level difference signal corresponding thereto, The present invention is characterized in that it includes DC level correction calculation means for correcting each DC level of the signals.

In the configuration described in item 1, any one of a plurality of signals may be used as the reference signal.

[Operation] In the DC level difference correction circuit of the present invention, each DC level of a plurality of signals is made to match the reference DC level by the two-stage calculation means of the DC level difference calculation means and the DC level correction calculation means.

Therefore, a phase shift due to a difference in DC level of a plurality of signals does not occur.

[Example] Hereinafter, the present invention will be explained in more detail based on the example shown in the drawings. Note that this invention is not limited to this.

In FIG. 1, instead of the preamplifier circuit 51 shown in FIG.
A preamplifier circuit 1 including a DC level difference correction circuit according to an embodiment of the present invention is used.

In this preamplifier circuit 1, the functions of the operational amplifier A1 and the operational amplifier A2 are the same as in the prior art. That is,
The output voltage VOI of operational amplifier A1 is VO1=Wa-R
2/R1+Va, and the output voltage VO2 of operational amplifier A2 is VO2=
Wb-R2/R1+Vb.

On the other hand, the negative input terminal of the operational amplifier A3 has a DC voltage Va
is input via the resistor Rs. Further, the negative input terminal of the operational amplifier A3 is connected to the output terminal via a resistor Rf.

Furthermore, the positive input terminal of operational amplifier A3 has a DC voltage v
A voltage obtained by dividing the difference between b and reference voltage EO by resistors Rs and Rf is input.

Therefore, if the output voltage of operational amplifier A3 is Ve, the voltage Vc at the negative input terminal is Vc=Ve-(Ve-Va)Rf/(Rf+Rs), and the voltage Vd at the positive input terminal is Vd=E1- (El-Vb)Rf/(Rf+Rs), but since it is Vc2Vcl according to Imaginary Show 1, from this, Ve=E1+(Vb-Va)Rf/Rs. Here, if Rf=Rs, Ve=E 1 + (Vb
-Va).

Similarly, the output voltage Vm of the operational amplifier Δ4 is Vm=
E 1 + (VO2-Ve), but if this is transformed, it becomes Vm=Wb-R2/R1+Va.

Therefore, from the perspective of comparator C1, the input voltage VOI
Since the DC levels of V and Vm are both Va and equal, only the changes are compared.

Thus, even if there is a difference in DC level between the signal voltages Vil and Vi2, no phase shift occurs in the pulse signal Pa.

[Effects of the Invention] According to the DC level difference correction circuit of the present invention, it becomes possible to match the DC levels of a plurality of signals having different DC levels and output the signals.

Therefore, for example, in a differential magnetic sensor having two or more phases, it is no longer necessary to select the magnetoresistive elements, thereby reducing the number of man-hours and improving the yield.

Further, for example, multi-phase and high multiplication are possible in order to increase the resolution of the rotary encoder.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a main part of a rotary encoder detection circuit including a DC level difference correction circuit according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing the configuration of a two-phase low-return encoder.
Figure 3 is a schematic diagram showing the element arrangement and connections of a two-phase differential magnetic sensor, Figure 4 is a circuit diagram of the main part of a conventional rotary encoder detection circuit, and Figures 5 (a) and (b) are the same as those shown in Figure 5. FIG. 3 is a signal waveform diagram of each part in the circuit. (Explanation of symbols) 1... Preamplifier circuit V including a DC level difference correction circuit
a, Vb... DC voltage A3 A4... Operational amplifier Vil, Vi2... Signal voltage.

Claims (1)

[Claims] 1. A plurality of DC signal output means for outputting DC signals of the same level as each DC level of the plurality of signals, and outputting a DC level difference signal by subtracting between the reference signal of the reference DC level and each of the DC signals. and DC level correction calculation means for correcting the DC level of each of the plurality of signals by subtracting between each of the plurality of signals and the corresponding DC level difference signal. A DC level difference correction circuit characterized by: