JP2001127556A - Differential amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove substrate low frequency noise together with high frequency noise with a simple circuit configuration. SOLUTION: A broadband noise removal means 100 that simultaneously removes low frequency noise and high frequency noise intruding via a semiconductor substrate is provided between a signal input terminal 2 and an input terminal of an amplifier 1. The broadband noise removal means 100 employs resistors R14, R24 and capacitors C11, C21. Electrodes 41, 51 which constitute the electrodes of respective capacitors are provided to the semiconductor substrate side via an insulation layer and connected respectively to signal input terminals 2, 3 via the respective resistors R14, R24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field of applications in which a single-ended signal is output from a differential signal with noise components removed, for example, AD conversion of a signal from a temperature sensor or a load cell by a single-ended input AD converter. Amplification circuit applicable to the field of signal conversion circuits, such as the field of signal conversion circuits for outputting intermediate signals generated by a fully differential circuit in a Δ 全 type DA converter as a single-ended signal, etc. About.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional differential amplifier circuit.

[0003] Differential signals of + Vi / 2 and -Vi / 2 are input to signal input terminals 2 and 3 of an amplifier 1 having two inputs and one output. The output terminal 4 of the amplifier 1 outputs a single-ended signal Vo.

Here, the gain of the differential amplifier circuit (Vo / V
The calculation for i) is as follows.

That is, the gain (Vo / Vi) is

[0006]

(Equation 1) Becomes

Here, the gain in the low frequency (s ≒ 0) region is as follows: Vo / Vi = −R ₂ / R ₁ (2)

The gain in the high frequency (s ≒ ∞) region is as follows: Vo / Vi = 1 / (C ₁ C ₂ R ₁ R ₃ s ² ) (3)

[0009]

FIGS. 6 and 7 show the structure of the CAP section when the differential amplifier circuit shown in FIG. 5 is provided on the semiconductor substrate 5. FIG.

On the semiconductor substrate 5, a first polysilicon layer 6 is formed via an insulating layer (not shown) made of silicon oxide or the like. On this first polysilicon layer 6, a second polysilicon layer 7 is formed via an insulating layer (not shown) made of silicon oxide or the like. The first polysilicon layer 6 is connected to a metal wiring 8 forming a part of the differential amplifier circuit, and the second polysilicon layer 7 is connected to a metal wiring 9 forming a part of the differential amplifier circuit. Have been.

Here, referring to the above-described differential amplifier circuit of FIG. 5, the first polysilicon layer 6 includes a capacitor 10
Corresponds to (volume C _1/2) One electrode 10a of the second polysilicon layer 7, a capacitor 10 (capacitance C _1/2)
Corresponds to the other electrode 10b.

In the above-described CAP structure, as shown in FIG. 7, a parasitic capacitance Cp exists between the first polysilicon layer 6 near the substrate surface and the semiconductor substrate 5.

When such a parasitic capacitance Cp exists, as shown in FIG.
n (voltage noise or the like) becomes a noise current, and enters the input side of the differential amplifier circuit along a path shown by arrow A.

That is, the noise current changes from the semiconductor substrate 5 →
Follow the path of the parasitic capacitance Cp → C ₁ electrode 1 → metal wiring 10 → the resistor R ₃ enters the input side of the amplifier 1. As a result, the noise current mixes with the input signal (differential signal), and
To the input side. As a result, the aforementioned (1) to
This has an effect on the gain shown by the equation (3).

Now, let the noise current mixed into the input signal be In
In = s · Cp · Vn (4) (where s = jω). This noise current In
This is a rather large value and will affect the measured value.

FIG. 9 shows another configuration example of the CAP structure.

The capacitance C _0/2 of the inverse parallel connection of capacitors 11 and 12 (i.e., connected to the input line of the opposite side of the metal wiring connected to the electrode side of the capacitor close to the substrate on the circuit) was constructed by In this case, it is assumed that parasitic capacitances Cp ₁ and Cp ₂ exist between the electrodes 11 a and 12 a of the capacitors 11 and 12 and the semiconductor substrate, respectively.

At this time, the noise current In mixed into the input signal is as follows: In = s (Cp ₁ · Vn ₁ -Cp ₂ · Vn ₂ ) (5) (where s = jω). Also in this case, the measured value is affected by the noise current In.

Here, the parasitic capacitances Cp ₁ and Cp ₂ of the circuit of FIG.
Let's talk about specific numerical values.

For example, C ₀ of the capacitors 11 and 12 is set to 1
Assuming that ₀ pF (that is, C 0/2 = 5 pF), in a normal semiconductor circuit, the parasitic capacitance between the semiconductor substrate and polysilicon (in FIG. 7, the semiconductor substrate 5 and the first polysilicon 6) is CAP. (The first polysilicon 6 in FIG. 7)
And about 1/10 to 1/2 of the capacity of the second polysilicon 7).
It has a value of 0. Now, assuming that it is 1/10, C _0/2
(= 5 pF), the parasitic capacitances Cp ₁ and Cp ₂ are 0.5 p
It becomes F.

The noise current In as shown in the above-mentioned equations (4) and (5) includes both high-frequency noise and low-frequency noise. Is low frequency noise.

However, in the conventional differential amplifier circuit as shown in FIG. 5 or FIG. 9, no measure is taken against the low frequency noise. That is, the noise current In mainly composed of low-frequency noise is changed from the semiconductor substrate 5 to the parasitic capacitance C.
p → C ₁ electrode 10a (first polysilicon 6) → metal wiring 10 → resistor R ₃ → enters the circuit following the path of input terminal 1b of amplifier 1, which adversely affects measured values. Become.

An object of the present invention is to provide a differential amplifier circuit which can effectively remove not only high frequency components but also low frequency components with a simple circuit configuration.

[0024]

SUMMARY OF THE INVENTION The present invention relates to a differential amplifier circuit comprising a two-input one-output amplifier that receives a differential signal and outputs a single-ended signal,
A semiconductor substrate, a circuit unit formed on the semiconductor substrate via an insulating layer, the circuit unit having at least the amplifier, and two input terminals of the amplifier constituting the circuit unit, respectively, and the differential signal is input to the circuit unit; Signal input terminal
A broadband noise removing unit connected between the signal input terminal and the input terminal of the amplifier, for simultaneously removing low-frequency noise and high-frequency noise entering through the semiconductor substrate; By using a resistor and a capacitor, one electrode constituting the capacitor is provided on the semiconductor substrate side via the insulating layer, and is connected to the signal input terminal side via the resistor, so that a differential amplifier circuit is provided. Is configured.

Here, the low-frequency noise enters from the semiconductor substrate via the insulating layer, via one electrode of the capacitor constituting the broadband noise removing means, and further enters one electrode of the capacitor. The low-frequency noise is prevented from entering the circuit section by tracing a path that is guided to and absorbed by the resistor from the resistor.

According to the present invention, there is provided a differential amplifier circuit comprising a two-input / one-output amplifier which receives a differential signal and outputs a single-ended signal, wherein one of the differential signals is an input. A first signal input terminal, and a first signal input terminal of the amplifier.
A first input line to which a first resistor and a second resistor are connected in series, a second signal input terminal to which the other of the differential signals is input, and a second input terminal of the amplifier A second input line in which a third resistor and a fourth resistor are connected in series, and a circuit in which a fifth resistor and a first capacitor are connected in series, wherein the fifth resistor is connected to the first resistor. A third input line connected to the first signal input terminal of the input line, wherein the first capacitor is connected between the third resistance and the fourth resistance of the second input line; A circuit in which a second capacitor is connected in series, the sixth resistor is connected to the second signal input terminal of the second input line, and the second capacitor is connected to the first resistor of the first input line. And a fourth input line connected between the second resistor and the second resistor. By obtaining, constituting a differential amplifier circuit.

Here, one electrode constituting the first capacitor of the third input line is provided on the semiconductor substrate side via an insulating layer, and the first signal input terminal is provided via the fifth resistor. One electrode constituting the second capacitor of the fourth input line is provided on the semiconductor substrate side via the insulating layer, and
It is connected to the second signal input terminal via a resistor.

The low-frequency noise is absorbed by being guided from the semiconductor substrate to the fifth resistor via one electrode of the third input line, which constitutes the first capacitor,
Alternatively, the low-frequency noise is supplied to the amplifier by tracing a path guided from the semiconductor substrate to the sixth resistor through one electrode constituting the second capacitor of the fourth input line and absorbed. Avoid entering the side.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Circuit Configuration) First, the circuit configuration of the differential amplifier circuit according to the present invention will be described with reference to FIG.

FIG. 1 shows a differential signal (+ Vi / 2, -Vi /
This is a differential amplifier circuit configured by using a 2-input / 1-output amplifier 1 which receives 2) as an input and outputs a single-ended signal (Vo). Hereinafter, the broadband noise removing unit 100 according to the present invention will be described in detail.

Reference numeral 20 denotes a first signal input terminal 2 to which a differential signal (+ Vi / 2) is input, and a first input terminal 1 of the amplifier 1
between the a, a first input line and a first resistor R ₁₁ and a second resistor R ₁₃ are connected in series.

Reference numeral 30 denotes a second signal input terminal 3 to which a differential signal (-Vi / 2) is input, and a second input terminal 1 of the amplifier 1.
between is b, a second input line and the third resistor R ₂₁ and the fourth resistor R ₂₃ are connected in series.

Reference numeral 40 denotes a fifth resistor R ₁₄ and a first capacitor C
₁₁ is connected in series, the fifth resistor R ₁₄ is connected to the first signal input terminal 2 of the first input line 20, and the first capacitor C ₁₁ is connected to the third resistor R of the second input line 30. _{twenty one}
If a third input line connected between the fourth resistor R _23.

Reference numeral 50 denotes a sixth resistor R ₂₄ and a second capacitor C
₂₁ is connected in series, the sixth resistor R ₂₄ is connected to the second signal input terminal 3 of the second input line 30, and the second capacitor C ₂₁ is connected to the first resistor R of the first input line 20. ₁₁
When a fourth input line connected between the second resistor R _13.

In addition, a resistor R ₁₂ and a capacitor C ₁₂ are connected between the first input line 20 side of the amplifier 1 and the output terminal 4. Between the second input line 30 side and the ground 60 of the amplifier 1, a resistor R ₂₂ and capacitor C ₂₂ is connected.

(CAP Structure) Here, the configuration of the CAP unit will be described with reference to FIGS.

In the above differential amplifier circuit, the first capacitor C ₁₁ of the third input line 40 and the second capacitor C ₂₁ of the fourth input line 50 constitute a CAP unit.

The first capacitor C ₁₁ of the third input line 40
Is formed on the first polysilicon layer 6
And is provided to face the semiconductor substrate 5 via an insulating layer (not shown).

In this case, it is assumed that a parasitic capacitance Cp ₁ exists between the electrode 41 (the substrate-side electrode of the first polysilicon layer 6 shown in FIG. 7) and the semiconductor substrate 5. Is assumed to be Vn ₁ .

On the other hand, one electrode 51 constituting the second capacitor C ₂₁ of the fourth input line 50 corresponds to the first polysilicon layer 6, and is connected to the semiconductor substrate 5 via an insulating layer (not shown). They are provided facing each other.

In this case, it is assumed that there is a parasitic capacitance Cp ₂ between the electrode 51 (the substrate-side electrode of the first polysilicon layer 6 shown in FIG. 7) and the semiconductor substrate 5. Is assumed to be Vn ₂ . (Gain) Next, the gain (Vo / Vi) of the differential amplifier circuit will be described with reference to FIG.

FIG. 2 is equivalent to the circuit of FIG. 1 described above, but here, in order to compare with the gain of the circuit shown in FIG. It has been simplified and replaced.

The gain (Vo / Vi) of the circuit shown in FIG.

[0045]

(Equation 2)

Is as follows.

Here, the gain in the low frequency (s ≒ 0) region is as follows: Vo / Vi = −R ₂ / R ₁ (7)

On the other hand, the gain in the high frequency (s ≒ ∞) region is as follows: Vo / Vi = 4R ₂ / {C ₁ C ₂ R ₁ (R ₁ R ₂ + R ₁ R ₃ +2)
Putting the ^{_{R 2 R 3) s 2}}} R 1 R 2 + R 1 R 3 = 2R 2 R 3, Vo / Vi = 1 / (C 1 C 2 R 1 R 3 s 2) ... a (8).

From the above results, equation (7) matches equation (2) of the conventional example, and equation (8) matches equation (3) of the conventional example. Therefore, it can be seen that the same gain can be obtained in both the low-frequency region and the high-frequency region even if the circuit configuration is different from the conventional one.

(Noise Current Path) Next, a noise current path will be described with reference to FIG.

(A) The current path of low frequency noise will be described.

The low frequency noise from the substrate noise Vn ₁ is
Through the parasitic capacitance Cp ₁ , it enters the electrode 41 of the capacitor C ₁₁ of the third input line 40, and goes to the signal input terminal 2 (usually low impedance) via the resistor R ₁₄ and is absorbed. As a result, the low-frequency noise does not go to the input terminals 1a and 1b of the amplifier 1, so that the low-frequency noise is not mixed into the differential signal of the low-pass filter.

Here, the noise current In of the low frequency noise is obtained. Now, for the sake of simplicity, the capacitor C _11, a value each C _0/2 of the capacitor C ₂₁ Distant, C _0/2 is C
Assume that it is sufficiently larger than p ₁ and Cp ₂ .

[0054]

(Equation 3) On the fourth input line 50 side, the substrate noise Vn
Low frequency noise from ₂ through the parasitic capacitance Cp _2, 4
It enters the electrode 51 of the capacitor C ₂₁ of the input line 50,
Resistor R ₂₄ via the signal input terminal 3 (typically low impedance) facing in the direction of, and is absorbed. Therefore, also in this case, since the low-frequency noise does not go to the input terminals 1a and 1b of the amplifier 1, the low-frequency noise is not mixed into the differential signal of the low-pass filter.

(B) The current path of high frequency noise will be described.

The high frequency noise from the substrate noise Vn ₁ is
Through the parasitic capacitance Cp ₁ and the capacitor C ₁₁ of the third input line 40, the current proceeds in the direction of the resistor R ₂₂ as shown by the arrow B.

On the other hand, the high-frequency noise from the substrate noise Vn ₂ travels through the parasitic capacitance Cp ₂ , the capacitor C ₂₁ of the fourth input line 50, and the direction of the resistor R ₁₂ as shown by the arrow C. Go by.

Here, the noise current In of the high frequency noise is obtained.

The noise current In ₁ from the substrate noise Vn ₁ side
Is

[0060]

(Equation 4) Becomes

Similarly, the noise current In ₂ from the substrate noise Vn ₂ side is:

[0062]

(Equation 5) Becomes

Then, a noise current In corresponding to the difference between the expressions (10) and (11) enters the circuit. The noise current In is

(Equation 6) Here, the value of the noise current In is obtained and compared with the conventional example.

Using the numerical values shown in the above-described conventional example,
Combined capacitance of C _0/2 = 5pF and Cp ₁ = 0.5 pF is
It becomes about 0.45 pF. Likewise, C _0/2 = 5pF and Cp
The combined capacitance when ₂ = 0.5 pF is about 0.45 pF. In contrast, in the conventional _{example, C 0/2 (= 5pF} )
Parasitic capacitances Cp ₁ and Cp ₂ are 0.5 pF. Therefore, it is understood that the present invention is smaller by the value of 0.5 pF−0.45 pF = 0.05 pF, and the effect on high-frequency noise is surely improved by the reduced amount.

FIG. 4 shows the relationship between the noise current and the frequency. Here, the present invention is compared with a conventional example.

As can be seen from FIG. 4, in the conventional low-pass filter circuit, substrate noise proportional to the frequency s is mixed in all frequency regions. On the other hand, according to the present invention, the same substrate noise as in the conventional circuit may be mixed in the high frequency region (point Q), or the mixed noise may be removed as the frequency decreases in the low frequency region (point R). Understand.

The reason why the point P has decreased to the point Q in the high-frequency region is that the value corresponds to the above-described decrease of 0.05 pF.

[0068]

As described above, according to the present invention,
Between the signal input terminal and the input terminal of the amplifier, there is provided broadband noise removing means for simultaneously removing low-frequency noise and high-frequency noise entering through the semiconductor substrate, and the wideband noise removing means uses a resistor and a capacitor, and One of the electrodes constituting the capacitor is provided on the semiconductor substrate side via an insulating layer, and is connected to the signal input terminal side via the resistor.
Penetrating from the semiconductor substrate through one electrode of the capacitor constituting the broadband noise removing means via the insulating layer,
Further, the low-frequency noise can be prevented from entering the circuit section by following a path guided from one electrode of the capacitor to the resistor and absorbed, whereby a high-frequency component can be obtained with a simple circuit configuration. Not only low-frequency components but also low-frequency components can be effectively removed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a differential amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a simplified circuit diagram showing the circuit of FIG. 1 for comparison with a conventional example.

FIG. 3 is a circuit diagram showing a path of a noise current.

FIG. 4 is a characteristic diagram showing a relationship between frequency and noise current.

FIG. 5 is a circuit diagram showing a conventional example.

FIG. 6 is a top view showing a planar structure of a CAP unit.

FIG. 7 is a sectional view showing an aa ′ section of the CAP section in FIG. 6;

FIG. 8 is a circuit diagram showing a path of a noise current in a conventional circuit.

FIG. 9 is a circuit diagram showing another configuration example of the CAP structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Amplifier 1a 1st input terminal 1b 2nd input terminal 2 1st signal input terminal 3 2nd signal input terminal 4 output terminal 6 1st polysilicon layer 7 2nd polysilicon layer 8, 9 Metal wiring 20 1st input Line 30 second input line 40 third input line 41 electrode 50 fourth input line 51 electrode 60 ground terminal 100 broadband noise removing means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03H 11/04 H01L 27/04 RF term (Reference) 5F038 AC02 AC05 AR27 AZ03 BH02 BH03 BH19 DF01 DF03 EZ20 5J066 AA01 AA12 CA41 FA16 HA25 HA29 QA04 TA03 5J092 AA01 AA12 CA41 FA16 HA25 HA29 QA04 TA03 UR12 UR13 UR14 5J098 AA11 AA14 AB03 AD11 CA02 CB10

Claims (5)

[Claims] 1. A differential amplifier circuit comprising a two-input / one-output amplifier that receives a differential signal and outputs a single-ended signal, comprising: a semiconductor substrate; A circuit unit formed via a layer and having at least the amplifier; a signal input terminal connected to each of two input terminals of the amplifier constituting the circuit unit to receive the differential signal; A broadband noise eliminator connected between a terminal and an input terminal of the amplifier and simultaneously removing low-frequency noise and high-frequency noise entering through the semiconductor substrate, wherein the broadband noise eliminator includes a resistor and a capacitor. And one electrode constituting the capacitor is provided on the semiconductor substrate side via the insulating layer, and the signal input terminal is provided via the resistor. A differential amplifier circuit which is characterized by being configured to connect to. 2. The low-frequency noise enters from the semiconductor substrate via the insulating layer through one electrode of the capacitor constituting the broadband noise removing means, and further from one electrode of the capacitor. The differential amplifier circuit according to claim 1, wherein the low-frequency noise is prevented from entering the circuit section by following a path guided to and absorbed by the resistor. 3. A differential amplifier circuit using a two-input / one-output amplifier that receives a differential signal and outputs a single-ended signal, wherein one of the differential signals is input. A first signal input terminal;
A first input line in which a first resistor and a second resistor are connected in series with a first input terminal of the amplifier; a second signal input terminal to which the other of the differential signals is input;
A second input line in which a third resistor and a fourth resistor are connected in series between the second input terminal of the amplifier and a circuit in which a fifth resistor and a first capacitor are connected in series; A fifth resistor is connected to the first signal input terminal of the first input line, and the first capacitor is connected to the second signal input terminal.
A circuit in which a third input line connected between the third resistor and the fourth resistor of the input line, and a sixth resistor and a second capacitor are connected in series, wherein the sixth resistor is connected to the third resistor. Connected to the second signal input terminal of the second input line, and the second capacitor is connected to the first signal input terminal.
A differential amplifier circuit comprising: a fourth input line connected between the first resistor and the second resistor of an input line. 4. An electrode of the third input line, which constitutes the first capacitor, is provided on the semiconductor substrate side via an insulating layer, and the first electrode is provided via the fifth resistor.
One electrode of the fourth input line, which is connected to a signal input terminal and constitutes the second capacitor, is provided on the semiconductor substrate side via the insulating layer, and the second signal is provided via the sixth resistor. The differential amplifier circuit according to claim 3, wherein the differential amplifier circuit is connected to an input terminal. 5. The low-frequency noise is guided from the semiconductor substrate to the fifth resistor via one electrode of the third input line and constituting the first capacitor, or is absorbed. The low-frequency noise enters the amplifier side by following a path guided from the semiconductor substrate to the sixth resistor through one electrode constituting the second capacitor of the fourth input line and absorbed. 5. The differential amplifier circuit according to claim 3, wherein the differential amplifier circuit is not operated.