JPH0738338A - Integrated circuit - Google Patents

Abstract

PURPOSE:To provide an integrated circuit capable of suppressing the lowering of S/N due to a high frequency electromagnetic noise voltage induced to a ground line GL, while keeping a simple circuit configuration. CONSTITUTION:A plus input terminal of a first stage integral amplifier circuit (first stage amplifier circuit) 11 is connected to a ground line GL through a capacitor C' and a resistance element Rb for reducing an EMI, which are connected in series to each other. Between the + input terminal of the first stage amplifier circuit 11 and the ground line GL, the capacity is connected by the capacitor C', therefore, an external high frequency electromagnetic noise voltage (EMI noise voltage) intrudes through the capacitor C', but a voltage drop is generated in the resistance element Rb by a charge/discharge current of the capacitor C', therefore, an EMI noise voltage Vn applied to the + input terminal is reduced by this voltage drop.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to integrated circuits.

[0002]

2. Description of the Related Art Conventionally, there is known an integrated circuit of a first stage integration system which employs a differential amplifier circuit which integrates and amplifies an input signal voltage as a first stage amplifier circuit. FIG. 2 shows an example of this first-stage integration type integrated circuit. Reference numeral 100 denotes a first-stage integral amplifier circuit, and the DC amplification factor Kdc of the operational amplifier 101 is R
If s / R = Rc / Ri, then Rs / R. The amplified and output AC voltage component is fed back to the negative input terminal through the feedback capacitor C for integration, and is suppressed, whereby integration is performed.

C'is a capacitor for phase compensation which connects the + input terminal and the ground line GL, and is a feedback capacitor C.
The same phase delay as the phase delay of the-input terminal potential due to is generated at the + input terminal to compensate (cancel) the phase delay of the output voltage. The integration time constant of the circuit is determined by CR. Also,
This is essentially the same when the input signal voltage Vi is not a differential voltage and there is a signal voltage 0 input to the − input end. In this case, the ground end G also serves as the input end B, so that the B terminal and the resistor are connected. Ri is omitted and Rc is an offset compensation resistor. Reference numeral 200 is an electronic circuit of the next stage that processes the integrated amplified voltage Vo input from the first-stage amplifier circuit 100.

The first-stage integration amplifier circuit 100 selectively amplifies a DC component or a low frequency component of the input signal voltage Vi while reducing a high frequency noise voltage mixed in the input signal voltage Vi or an unnecessary AC component in the signal voltage. it can.

[0005]

However, since the above-described first-stage integral amplifier circuit 100 is capacitively connected to the ground line GL through the capacitor C ′, the high-frequency electromagnetic noise voltage (so-called) induced on the ground line GL (so-called). There is a big problem that the EMI noise voltage) penetrates into the + input terminal of the operational amplifier 100 through the capacitor C ′ and reduces the SN ratio of the output voltage. In particular, this problem has been a very important issue in vehicle electronic devices installed in an engine room where the vehicle body potential is artificially set to the ground potential and spark discharge is frequently performed.

As a solution to this problem, it may be considered that only the input signal voltage is amplified in the first stage and the integration circuit is integrated in the second stage. However, in this case, it is necessary to connect the operational amplifiers in two stages, which causes problems such as a complicated circuit configuration, an increase in internal noise voltage, and an increase in power consumption. The present invention has been made in view of the above problems, and provides an integrated circuit capable of favorably suppressing a decrease in SN ratio due to a high frequency electromagnetic noise voltage induced in a ground line GL while maintaining a simple circuit configuration. Is the purpose.

[0007]

An integrated circuit according to the present invention has a capacitor having one electrode connected to an input end and the other end connected to a ground line, and a signal voltage is input to the input end from the outside. In an integrated circuit equipped with a first-stage amplifier circuit,
The first-stage amplifier circuit is characterized by including a resistance element connected in series with the capacitor for reducing EMI.

In one aspect, the capacitor is a phase compensating capacitor of the first-stage integration amplifier circuit. Further, when the first-stage integration amplifier circuit is an operational amplifier type in which the input terminal and the output terminal are connected by a feedback capacitor, a resistance element having a resistance value corresponding to the feedback capacitor in series is provided in accordance with this resistance element, Phase compensation is possible.

[0009]

The input end of the first-stage amplifier circuit is connected to the ground line through a capacitor and a resistance element that are connected in series with each other. The resistance element that is a feature of the present invention is for reducing EMI. When a capacitor is connected between the input end of the first-stage amplifier circuit and the ground line, the external high frequency electromagnetic noise voltage (EMI noise voltage) mainly enters through this capacitor. That is, since the signal voltage is extremely small at the input end of the first-stage amplifier circuit, the external high frequency electromagnetic noise voltage that enters and is superimposed on the signal voltage greatly deteriorates the SN ratio.

The resistor element connected in series with the capacitor newly provided in the present invention reduces the external high frequency electromagnetic noise current flowing to the input end of the first stage amplifier circuit through this capacitor,
This greatly improves the EMI resistance of the integrated circuit. Further, the newly provided resistance element can be easily integrated as a monolithic or hybrid integrated circuit, and does not complicate the circuit configuration or increase power consumption.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the integrated circuit of the present invention will be described with reference to FIG. This integrated circuit includes a first-stage integration amplifier circuit 11 in which an input signal voltage Vi is input to its differential input terminals A and B.
And an electronic circuit 2 that processes the output voltage of the first-stage integral amplifier circuit 11 and outputs a desired signal voltage Vo.

The first-stage integration amplifier circuit 1 has an input signal voltage Vi.
Is an operational amplifier circuit that integrates and amplifies, the negative input terminal of the operational amplifier 11 is connected to the input terminal A of the integrated circuit through the resistor R, and the positive input terminal is connected to the input terminal B of the integrated circuit through the resistor Ri. These differential input terminals A and B
The signal voltage Vi is input between them. The output terminal of the operational amplifier 11 is connected to the-input terminal through the feedback capacitor C and the resistor Ra connected in series with the feedback capacitor C, and the output terminal of the operational amplifier 11 is connected to the-input terminal through the resistor Rs.

The + input terminal of the operational amplifier 11 is grounded to the ground electrode (vehicle body) through the resistor Rc, the internal ground line GL 'and the ground line GL. Similarly, the + input terminal of the operational amplifier 11 is connected to the internal ground line G through the capacitor C ′ and the resistor Rb connected in series with the capacitor C ′.
It is grounded to the ground electrode (vehicle body) through L ′ and the ground line GL.

In this embodiment, R = Ri, Rs = Rc,
Ra = Rb and C = C '. The operation of the first-stage integral amplifier circuit 1 will be described below. The DC amplification factor Kdc of the operational amplifier 101 is Rs / R. The AC signal component of the input signal voltage Vi is amplified by the operational amplifier 11, fed back to the negative input terminal through the feedback capacitor C for integration, and suppressed.
As a result, integration, that is, the AC signal component of the input signal voltage Vi is reduced. The integration time constant of the circuit is determined by CR.

C'is a capacitor for phase compensation which connects the + input terminal and the ground line GL, and is a feedback capacitor C.
The same phase delay as the phase delay of the-input terminal potential due to is generated at the + input terminal to compensate (cancel) the phase delay of the output voltage. The resistor Rb (resistive element in the present invention), which is a feature of this embodiment, is used to charge and discharge the capacitor C ′ by the external high frequency electromagnetic noise voltage (EMI noise voltage) Vn induced in the ground line GL and the internal ground line GL ′. A voltage drop is generated with respect to the current, and the EMI noise voltage Vn applied to the + input terminal of the operational amplifier 11 is reduced.

Thus, the EM resistance of the first-stage integral amplifier circuit 1 is improved.
The I noise characteristic is significantly improved. However, by connecting the resistor Rb in series with the phase compensating capacitor C ′, the phase of the phase compensating current flowing through the phase compensating capacitor C ′, that is, the phase of the voltage applied to the + input terminal also changes again. I will end up. Therefore, in the present embodiment, by connecting the resistor Ra in series with the feedback capacitor C, the phase of the voltage applied to the-input end is changed again in the same manner, whereby the potential of the + input end due to the resistor Rb is changed. The effect of the phase change is offset.

Of course, the resistance Ra changes the integration time constant, which can be compensated by adjusting the resistance value of the resistance R. In a preferred example, capacitor C'and resistor Rb
Is a low-pass filter when viewed from the EMI noise voltage Vn, and the band of the EMI noise voltage Vn is several tens of M
Since it is above Hz, the time constant C'Rb is 10
^-8 to 10 ^-9 .

In the above embodiment, R = Ri, Rs = R
Although c and C = C ′ have been described, it is natural that the effect can be obtained even if the equivalence relation between them is not strict. Also, R = R
Instead of i, Rs = Rc, C = C ′, Rs / R =
It may be Rc / Ri. In this case, it is preferable to set Ri = CR / C ′ in order to make the time constant C′Ri on the + input end side equal to the time constant CR on the −input end side.

Further, in order to make the time constant CRa on the feedback end side equal to the time constant C'Rb on the + input end side, Ra =
C'Rb / C is preferable. Further, the input signal voltage Vi may be a signal voltage input to the-input terminal instead of the differential voltage. In this case, the ground end G is the input end B
Therefore, the B terminal and the resistor Ri are omitted, and Rc is the value of R / Rs as an offset compensation resistor.

In this way, although a simple circuit configuration for performing amplification and integration in the first stage and reduction in power consumption can be realized, the SN ratio is favorably reduced due to the high frequency electromagnetic noise voltage induced in the ground line GL. It can be suppressed, and is particularly effective in in-vehicle electronic device applications.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an integrated circuit of this embodiment.

FIG. 2 is a circuit diagram of a conventional integrated circuit.

[Explanation of symbols]

1 is a first-stage integral amplifier circuit, C'is a capacitor, Rb is a resistor (resistive element)

Claims (1)

[Claims] 1. An integrated circuit comprising a first-stage amplifier circuit in which one electrode is connected to an input end and the other end is connected to a ground line, and a signal voltage is input to the input end from the outside, An integrated circuit characterized in that the first-stage amplifier circuit comprises a resistance element for reducing EMI, which is connected in series with the capacitor.