JP2001203543A - Integrated amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a pole due to a parasitic capacitance from being caused in a transfer function of a feedback circuit having a feedback resistive element and a feedback phase compensation capacitive element. SOLUTION: In the case of configuring a feedback amplifier circuit with an integrated circuit, the capacitance of feedback phase compensation capacitors C11, C12 and the resistance of feedback resistors R11, R12 are selected so that a relation of C11.R11=(C12+Cp11).R12 holds. Thus, the production of a pole to a transfer function of the feedback circuit due to a parasitic capacitance Cp11 of the feedback phase compensation capacitor C12 is prevented and only one zero is in existence in the transfer function. As a result, an advanced phase compensation function in the feedback circuit can normally be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated amplifier circuit using a bipolar monolithic integrated device.
When realizing a wideband and high gain amplifier circuit such as an optical disk pickup element by applying a negative feedback to an operational amplifier, an integration that requires a capacitance value equal to or less than a minimum value of a capacitance element restricted by a design rule of the integration element is required. It relates to an amplifier circuit.

[0002]

2. Description of the Related Art The read / write speed of an amplifier circuit such as an optical disk pickup element for receiving and amplifying an optical signal has been dramatically increased. Also,
The amount of light used has been reduced due to the increase in types of usable disks and the demand for lower voltage and lower current consumption of units. As described above, the amplifier circuit is required to have a wider band and a higher gain.

When the above-mentioned amplifier circuit is realized by applying a negative feedback to an operational amplifier, a circuit using an inverting amplifier as shown in FIG. 3 is conceivable. Here, PD1 is a photodiode for receiving signal light, A1 is an operational amplifier, R1 is a feedback resistor, C1
1 is a capacitance for phase compensation in the feedback circuit.

In this amplifier circuit, the role of the capacitor C1 for phase compensation in the feedback circuit is mainly that of the capacitance component Cpd1 of the photodiode PD1 connected to the input terminal of the operational amplifier A1, the feedback resistor R1 and the operational amplifier. Due to the parallel resistance of the input impedance Zi1 of the input terminal of A1, a pole having a frequency corresponding to τp = Cpd1 · (R1‖Zi1) is generated in the transfer function of the feedback circuit, τz = C1 ·
An object of the present invention is to prevent a loop phase of a feedback amplifier circuit from being excessively delayed by canceling out a zero point at a frequency corresponding to R1.

In order to widen the bandwidth of the amplifier circuit, if the amplification band of the operational amplifier A1 is sufficient, the speed of the photodiode PD1 is increased (that is, the capacitance component Cpd1 is reduced). Due to this reduction of Cpd1, the pole formed in the transfer function of the feedback circuit moves to the high frequency side according to the above equation. However, in this case, unless the zero created by the phase compensation circuit is also moved to the high frequency side, the zero cannot be canceled with the pole.
The band cannot be widened, or the feedback becomes unstable and oscillates. That is, it is necessary to reduce the value of τz = C1 · R1.

In order to increase the gain of the amplifier circuit, the feedback resistor R1 determines the gain of the entire feedback amplifier circuit. Therefore, it is necessary to increase the feedback resistor R1.

When these factors are combined, it is necessary to reduce the value of the phase compensation capacitance C1 of the feedback circuit with the increase in the bandwidth and the gain of the amplifier.

On the other hand, as a capacitance element usable in a bipolar monolithic integrated element, there are a capacitance between a PN junction and a capacitance using a silicon oxide film or a silicon nitride film as a dielectric.
(Hereinafter, referred to as an oxide film capacitance or a nitride film capacitance). Among them, the capacitance element such as an oxide film capacitance and a nitride film capacitance has a small variation in capacitance value due to the polarity between the capacitance elements and the applied voltage and a small production variation in the absolute value of the capacitance. As shown in FIG. 4, these capacitive elements include a SiO ₂ film and a Si ₃
It has a structure in which a dielectric film 1 such as an N ₄ film is sandwiched between an electrode 2 and an N ⁺ diffusion region 3. The capacitance value is determined by the thickness of the dielectric film 1 and the electrode 2 in contact with the dielectric film 1. It is the contact area.
4 is a diffusion side electrode, 5 is an N-type epitaxial layer, and 6 is a P-type substrate.

Here, for the reasons described above, when attempting to make a capacitance element having a small capacitance value, it is necessary to increase the thickness of the dielectric film 1 or to reduce the contact area of the electrode 2 in contact with the dielectric film 1. One of However, in general, the thickness of the dielectric cannot be easily changed because it may affect the performance of other elements. Therefore, the area of the electrode 2 that contacts the dielectric film 1 is reduced. However, since the electrode 2 is formed by etching a metal film for an electrode, the manufacturing variation regarding the size of the electrode 2 is due to a shift in the etching amount. Therefore,
As the electrode size decreases, the error increases as a square function. Conversely, if the manufacturing variation of the capacitive element is to be kept within a certain range, the minimum value of the electrode size is determined, and the minimum value of the capacitance is determined. That is, in any case, the capacitance C1 for phase compensation in the feedback circuit cannot be reduced.

As a method of solving this problem, as shown in FIG. 5, by connecting a plurality of capacitance elements in series, the total capacitance value is reduced to a small value while the capacitance value per capacitance element is not reduced. There is a way to For example, when n stages of capacitance elements having the same capacitance value Ca are connected in series, the total capacitance value C becomes C = Ca / n, and by increasing the number of stages n, a value as small as the circuit scale allows is possible. Can be created.

[0011]

However, the conventional inverting amplifier having a feedback circuit including a capacitance formed by connecting a plurality of capacitance elements in series has the following problems. That is, the integrated capacitive element has a structure in which the dielectric film 1 is sandwiched between the electrode 2 and the diffusion region 3 as shown in FIG.
The capacitance between the PN junctions between the substrates 6 is necessarily added. Therefore, when a capacitance formed by connecting a plurality of the above-mentioned capacitance elements in series is applied to the inverting amplifier shown in FIG. 3, in an actual circuit, as shown in FIG. , Capacitance Cp between PN junction between diffusion region and substrate
Will be attached as parasitic capacitance.

The parasitic capacitance Cp is always attached to one capacitance element Ca irrespective of the series connection of the capacitance elements Ca, and is used for phase compensation in a feedback circuit as shown in FIG. Even in the case of an inverting amplifier in which the capacitance C1 is formed by one capacitance element, one terminal of the capacitance C1 actually has a parasitic capacitance (not shown). However, generally, the impedance of the output terminal of the operational amplifier A1 is low. Therefore, the terminal on the diffusion region side having the parasitic capacitance is connected to the operational amplifier A1.
, It is possible to prevent the pole formed by the parasitic capacitance from appearing only when the frequency is so high that there is no practical problem. Therefore, there is no need to consider this parasitic capacitance as a problem.

However, as shown in FIG. 6, when the feedback resistance is divided into a plurality of parts and the parasitic capacitances Cp are connected one by one between the connection point of each feedback resistance element R and the substrate potential,
Each parasitic capacitance Cp generates a pole determined by the product of the impedance at the corresponding connection point. for that reason,
As a result, the feedback resistor R and the capacitor C connected in series are connected.
Even if a desired zero can be created as a whole, a pole is generated at each point inside the series connection, which greatly deviates from the design transfer function. Therefore, there is a problem that the performance as designed as the feedback amplifier cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wide-band and high-gain integrated amplifier circuit capable of preventing a transfer function of a feedback circuit having a feedback resistance element and a feedback phase compensation capacitance element from having a pole caused by a parasitic capacitance. To provide.

[0015]

According to a first aspect of the present invention, an operational amplifier having at least two positive and negative input terminals is connected between an output terminal and a negative input terminal of the operational amplifier. And an integrated amplifier circuit integrated with the negative feedback circuit, wherein the negative feedback circuit is configured by serially connecting a plurality of parallel circuits each having a resistance element and a capacitance element connected in parallel. The number of parallel circuits constituting the negative feedback circuit is M, N is the number of the parallel circuit, and the side closer to the negative input terminal of the operational amplifier among any two parallel circuits connected in series to each other The value of the resistance element constituting the parallel circuit of R is set to R (N), while the value of the capacitance element is set to C (N), and the resistance element forming the parallel circuit near the output terminal of the operational amplifier is set to R (N). Is R (N + 1), The value of the serial capacitance element C (N
+1), and the value of the parasitic capacitance between the capacitive element in which the diffusion-side capacitive electrode is connected to the connection point of the above four elements and the substrate is Cp (N), and 1 ≦ N ≦ (M−1) The above values R (N), C (N), and C (N) · R (N) = {C (N + 1) + Cp (N)} · R (N + 1) in the range of R (N +
1), C (N + 1) is set.

According to the above configuration, each value R (N), C (N), R (N +) of the resistance element and the capacitance element constituting the feedback circuit is provided.
1), C (N + 1) is in the range of 1 ≦ N ≦ (M−1), and the equation C (N) · R (N) = {C (N + 1) + Cp (N)} · R (N + 1) It is set to hold. Therefore, the value R
Each resistance element of (1) to value R (M−1), value C (1) to value C (M−
The circuit block including each capacitance element of 1) and each parasitic capacitance of values Cp (1) to Cp (M-2) has a resistance element of value R and a value Cp.
Is equivalent to a parallel circuit with the capacitive element. Therefore, the parasitic capacitance (Cp (M−
1)), the poles generated in the transfer function of the feedback circuit are canceled by one of the two zeros. As a result, the transfer function is represented by τz = C (M) · R (M). The zero that is
Only one. Therefore, the advance phase compensation function in the feedback circuit operates normally.

The integrated amplifier circuit according to the first aspect of the present invention includes:
It is desirable that the values of the respective capacitors constituting the respective parallel circuits are all set to the same value.

According to the above configuration, the values of the capacitors constituting each of the parallel circuits are all set to the same value.
Therefore, each of the above-mentioned capacitance elements is formed on the substrate with the same shape. In this way, the relative variation in the capacitance value of each of the above-mentioned capacitance elements that occurs during the manufacture of the integrated amplifier circuit is minimized.

The integrated amplifier circuit according to the first aspect of the present invention includes:
It is desirable that the values of the respective resistance elements constituting the respective parallel circuits are all set to the same value.

According to the above configuration, the values of the respective resistance elements constituting the respective parallel circuits are all set to the same value.
Therefore, each of the resistance elements is formed on the substrate with the same shape. Thus, the relative variation of the capacitance value of each of the resistance elements, which occurs during the manufacture of the integrated amplifier circuit, is minimized.

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
The number of the parallel circuits constituting the negative feedback circuit and the time constant of each of the parallel circuits may be set such that the value of the capacitance element constituting each of the parallel circuits is larger than the value of the parasitic capacitance of the capacitance element. desirable.

The above-mentioned capacitive element has a structure in which a dielectric film is sandwiched between an electrode and a diffusion region. On the other hand, the parasitic capacitance attached to the capacitor is P-
This is a capacitance between N junctions, and the structure is different. Therefore, it is difficult to achieve matching between the capacitive element and the parasitic capacitance. According to the above configuration, since the value of the capacitance element is larger than the value of the parasitic capacitance, even when the matching between the capacitance element and the parasitic capacitance is deteriorated, the time constant of the corresponding parallel circuit is reduced. The gap is small. Further, since the value of the capacitance element is larger than the value of the parasitic capacitance, the time constant difference between the right side and the left side when the above equation is satisfied is reduced, and the matching of each element is improved. .

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
The capacitive element forming each of the parallel circuits is connected such that the terminal to which the parasitic capacitance formed between the substrate and the substrate is connected is closer to the output terminal of the operational amplifier than the other terminal. It is desirable.

According to the above configuration, each of the capacitance elements is connected such that the terminal to which the parasitic capacitance is connected is located closer to the output terminal of the operational amplifier. Therefore, the parasitic capacitance of the capacitance element directly connected to the output terminal of the operational amplifier is also directly connected to the output terminal of the operational amplifier. The output impedance of the operational amplifier is low. As a result, the pole generated by the output impedance and the M-th resistive element has a very high frequency, and the above equation regarding the M-th parasitic capacitance need not be considered. Thus, the number of equations to consider is reduced.

Further, an integrated amplifier circuit according to a second aspect of the present invention includes an operational amplifier having at least two positive and negative input terminals, and a negative feedback circuit connected between an output terminal and a negative input terminal of the operational amplifier. , An integrated integrated amplifier circuit, wherein the negative feedback circuit is configured by connecting a plurality of parallel circuits formed by connecting a resistance element and a capacitance element in parallel, and each of the resistance elements And the value of each capacitive element and the number of parallel circuits constituting the negative feedback circuit are set so that a predetermined number of poles and zeros of a predetermined frequency are generated in a transfer function of a loop including the operational amplifier and the negative feedback circuit. It is characterized by doing.

According to the above configuration, the value of the resistance element and the capacitance element of each parallel circuit constituting the negative feedback circuit and the number of the parallel circuits constituting the negative feedback circuit are determined by the transfer function of the loop of the negative feedback amplifier. It is set to generate a predetermined number of poles and zeros of a predetermined frequency. In this way, other poles and zeros other than the negative feedback circuit can be canceled or the frequency characteristics and the like of the integrated amplifier circuit are intentionally manipulated.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a circuit diagram of a feedback amplifier circuit as an integrated amplifier circuit of the present embodiment. In FIG. 1, PD11 is a photodiode for receiving signal light, A
11 is an operational amplifier, R11 and R12 are feedback resistors, C11 and C12 are capacitors for phase compensation of the feedback circuit, Cp11 is a parasitic capacitor between the diffusion region in the capacitor C11 and the substrate, and Cp12 is a capacitor C1.
This is the parasitic capacitance between the diffusion region and the substrate in 2. In this case, the present feedback amplification circuit amplifies the signal from PD11 with a gain of (R11 + R12).

In the feedback amplifier circuit having the above configuration, it is assumed that the operational amplifier A11 is an ideal operational amplifier having an amplification factor A at all frequencies. Then, the feedback resistor R
The loop gain T of the feedback circuit composed of 11, R12, capacitances C11, C12 and parasitic capacitances Cp11, Cp12 is expressed by equation (1). T = A ・ (1 + s ・ C11 ・ R11) ・ (1 + s ・ C12 ・ R12) / [(1 + s ・ C11 ・ R11) ・ R12 + {1 + s ・ (C12 + Cp11) ・ R22} ・ R11] (1) where s = Jω.

Thus, R11, R12, C11, C12, Cp11,
The feedback circuit composed of Cp12 has τz1 = C11 · R11 and τz2 = C
It has a zero point at 12 and R12. Further, from the denominator of the above equation (1), there is a pole at τp = (C11 + C12 + Cp11) · (R11‖R12).

Here, when C11.R11 = C12.R12, assuming that Cp11 = 0, τp = (2.C11). (R11 / 2) = C11.R11 (2) τz1 (or τz2) becomes equal to τp. As a result, .tau.z1 (or .tau.z2) and .tau.p cancel each other, resulting in only one zero at .tau.z = C11.R11. Therefore, the advance phase compensation function in the feedback circuit operates normally.

However, the "problem to be solved by the invention"
As described above, when the feedback amplifier circuit is configured by an integrated element, the parasitic capacitance cannot be eliminated. That is, Cp11 does not become zero. Therefore, the frequency of the pole is shifted to a lower frequency than the frequency represented by the equation (2), and as a result, a pole is formed at a frequency lower than the zero point, so that τz1
(Or τz2) and τp cannot cancel each other out, causing a deviation from the design in the transfer function of the compensation circuit.

Therefore, in the present embodiment, in the feedback amplifier circuit shown in FIG. 1, C11.R11 = (C12 + Cp11).
Adjust the capacitance C12 and the feedback resistor R12 so as to obtain R12. Then, in the above equation (2), τp = (C11 + R11 / R12 · C11) · (R11‖R12) = C11 · R11 (3), so that τz1 and τp have exactly the same value. As a result, τz1 and τp cancel each other, resulting in τz
Only 2 will remain. Therefore, there is no unnecessary pole and only one zero point, and the advanced phase compensation function in the feedback circuit operates normally.

As shown in FIG. 2, the number of stages in the series connection when connecting a parallel circuit in which the feedback phase compensation capacitance and the feedback resistor of the feedback circuit are connected in parallel is three.
Even in the case of a two-stage feedback amplifier circuit, the concept of the two-stage feedback amplifier circuit described above can be applied as follows. First, C21
R21 = (C22 + Cp21) · Capacitance C21, C such that R22
22 and the feedback resistors R21 and R22 are adjusted. By doing so, a T-shaped circuit block composed of R21, R22, C21, C22, and Cp21 is connected in parallel with a resistor and a capacitor having a time constant of C22 · R22 and a resistance component of (R21 + R22). It can be considered equivalent to a circuit. Therefore, as shown in FIG. 2, the T-shaped circuit block is connected to a resistor R (= R2
If a parallel circuit of 1 + R22) and a capacitor C (= C22.R22 / (R21 + R22)) is replaced, the circuit becomes the same as the feedback amplifier circuit shown in FIG. 1, and the equation (4) can be set as in the case of FIG. C · R = (C23 + Cp22) · R23 ... (4)

Here, C = C22 · R22 / (R21 + R22), R
= (R21 + R22), Equation (4) can be transformed into Equation (5). {C22 · R22 / (R21 + R22)} · (R21 + R22) = C22 · R22 = (C23 + Cp22) · R23 (5) Therefore, the capacitances C22 and C23 are set so that the equation (5) is satisfied.
And the feedback resistors R22 and R23 may be adjusted.

That is, in the case of a three-stage series-connected feedback amplifier circuit shown in FIG. 2, each capacitance element and feedback resistor are set so that C21 ・ R21 = (C22 + Cp21) ・ R22 C22 ・ R22 = (C23 + Cp22) ・ R23. By setting the values of the elements, the occurrence of unnecessary poles is prevented and the number of zeros is reduced to one, just as in the case of a two-stage series-connected feedback amplifier circuit. Therefore, the advance phase compensation function in the feedback circuit operates normally.

The above is true for a feedback amplifier circuit in which the parallel circuit has three or more stages connected in series, by repeating the same procedure to obtain the same result as a feedback amplifier circuit having two stages in series connection. It means becoming.

That is, an arbitrary two-stage series connection portion of a plurality of series connections of the parallel circuits constituting the feedback circuit is considered. Then, of the two-stage series connection, R (N) and C (N) (N: the number of the parallel circuit, respectively) represent the resistance element and the capacitance element of the parallel circuit located closer to the negative input terminal of the operational amplifier A. ), And each of the resistance element and the capacitance element of the parallel circuit positioned closer to the output terminal of the operational amplifier A is represented by R
Assuming that (N + 1) and C (N + 1), in the range of 1 ≦ N ≦ (M−1), the expression (6) C (N) · R (N) = {C (N + 1) + Cp (N)} · R (N + 1) ... (6) such that R (N), C (N), R (N + 1), C (N +
By setting the value of 1), there is only one zero represented by the following equation (7): τz = C (M) · R (M) (7) Therefore, the advance phase compensation function in the feedback circuit operates normally. Note that M is the number of stages of the series connection. Also,
N is “1” for the parallel circuit located closest to the negative input terminal of the operational amplifier A.

Further, according to the above equation (6), the resistance element R (N)
When the values of all the capacitance elements C (N) (1 ≦ N ≦ (M−1)) are equalized when determining the respective values of the capacitance elements C (N), Can be made uniform, so that manufacturing variations that occur when a feedback amplifier circuit is formed by the integrated elements can be minimized. Therefore, a stable feedback amplifier circuit can be configured by accurately setting the time constant.

In this case, however, the resistance element R (N) connected in parallel to each capacitance element C (N) is the resistance element R (1) located closest to the negative input terminal of the operational amplifier A. It becomes smaller sequentially from. Therefore, the resistance values of the M resistance elements R (N) connected in series are all different. If this adversely affects the manufacturing variations of the resistance elements, on the contrary, the values of all the resistance elements can be equalized. However, in this case, all the capacitance elements have different values.
Whether the values of all the resistive elements are equal or the values of all the capacitive elements are equal may be selected so as to make the one in which the manufacturing accuracy against the shape change of the element is disadvantageous.

As described above, in the present embodiment,
A feedback amplifier circuit for applying a negative feedback to the operational amplifier by a feedback circuit is configured by an integrated circuit. In that case, the capacitance value of each capacitance element is reduced by configuring the feedback circuit by connecting a plurality of parallel circuits in which a capacitance element for phase compensation and a feedback resistance element are connected in parallel in series. Instead, the capacitance value of the compensating circuit is reduced to deal with the shift of the pole, which can be a transfer function of the feedback circuit, to the high frequency side accompanying the increase in the bandwidth and the gain.

In this case, the number of series connection of the parallel circuit of the resistance element R and the capacitance element C constituting the feedback circuit is M, and the number of the parallel circuits connected from the side closest to the negative input terminal of the operational amplifier A is M. And N, and the resistance element and the capacitance element of the parallel circuit near the negative input terminal of the operational amplifier A among the two parallel circuits adjacent to each other in the series-connected parallel circuit are denoted by R.
(N), C (N), the resistance element and the capacitance element of the distant parallel circuit are R (N + 1), C (N + 1), and the parasitic capacitance of the capacitance C (N) in the Nth parallel circuit is Cp. (N)
Within the range of 1 ≦ N ≦ (M−1), C (N) · R (N) = {C (N +
1) + Cp (N)} · R (N + 1), so that R (N),
The values of C (N), R (N + 1) and C (N + 1) are set.

This prevents the transfer function of the feedback circuit from generating an unnecessary pole due to the parasitic capacitance Cp (N), and prevents the M-th parallel circuit connected to the output terminal of the operational amplifier A from being closest to the output terminal. Frequency τ represented by the time constant of the circuit
It is possible to have only one zero at z = C (M) .R (M). Therefore, the advance phase compensation function in the feedback circuit can be normally operated. That is, according to the present embodiment, the performance as calculated as the feedback amplifier circuit can be exhibited.

The parallel circuit as shown in FIG.
In a feedback amplifier circuit connected in series, C21 · R21 =
As described above, if the equation of (C22 + Cp21) .R22 is satisfied, the feedback circuit functions as a leading phase compensation circuit having only one zero point. However, if this equation is not intentionally established, as described above, there are two zeros with a time constant of τz1 = C11 · R11 τz2 = C12 · R12, and τp = (C11 + C12 + Cpl1) · (R11‖R12) With this time constant, one pole can be formed. Since these equations hold in any case, the distance between the pole and the zero point can be intentionally increased or decreased. Therefore, using this characteristic, it is possible to cancel another pole or zero other than the feedback circuit, or to control the frequency characteristic of the negative feedback amplifier circuit by adjusting the gain-phase characteristic of the entire loop. is there.

From the above general equation (6) for canceling the parasitic capacitance, C (N) ＮR (N) = {C (N + 1) + Cp (N)} ・ R (N + 1) (6) As the value of the parasitic capacitance Cp (N) increases, the parallel circuit of the feedback resistance element R (N) and the feedback phase compensation capacitance element C (N) connected to the parasitic capacitance and the feedback resistance element R (N + 1), the feedback The difference in the time constant between the phase compensation capacitance element C (N + 1) and the parallel circuit is widened. In this case, from the above equation (6), the difference in the time constant is caused by the addition of the parasitic capacitance Cp (N) to the feedback phase compensation capacitance element C (N + 1). When the parasitic capacitance Cp (N) is larger than the above, the time constant difference between the N-th parallel circuit and the (N + 1) -th parallel circuit becomes more than twice, which causes a mismatch between the feedback phase compensation capacitance elements. easy. Further, as shown in FIG. 4, the feedback phase compensation capacitance element has a structure in which the dielectric film 1 is sandwiched between the electrode 2 and the diffusion region 3, whereas the parasitic capacitance is the capacitance between the diffusion region 3 and the substrate 6. −N junction capacitance, different structure. Therefore, the matching between the two types of capacitive elements is worse than that between the same type of feedback phase compensation capacitive elements, and an increase in the parasitic capacitance promotes a deterioration in the matching variation of the capacitance value. As a result, the possibility of deviating from the desired transfer function increases.

To prevent the above, the parasitic capacitance Cp
The time constant and the number of stages of the series connection may be set so that the value of the feedback phase compensation capacitive element C (N + 1) becomes larger than the value of (N). By doing so, it is possible to reduce the deviation of the time constant between the left side and the right side in the parasitic capacitance canceling equation (6) set for each parasitic capacitance.

If the number of serially connected stages of the parallel circuit is increased, the number of equations to be established increases proportionately, and it becomes difficult to establish all equations. In some cases, there is an equation with a deviation in the time constant.
However, even in that case, since the amount of shift and the polarity of the time constant between the left side and the right side according to one equation differ for each equation, the feedback circuit as a whole has the pole and zero on the transfer function. The positional relationship does not significantly deviate in one direction.

Also, as in the feedback amplifier circuit shown in FIG.
When an output voltage of the operational amplifier A is connected to a negative input terminal of the operational amplifier A through a feedback resistor R to form a negative feedback amplifier circuit, the operational amplifier A generally has a low output because it has a voltage input and a voltage output. Impedance and high input impedance. When a feedback circuit formed by connecting the parallel circuits in series as in the present embodiment is applied thereto, the parasitic capacitance Cp attached to each feedback phase compensation capacitance C is connected to the output terminal side of the operational amplifier A. When the feedback phase compensation capacitors C are arranged as described above, the parasitic capacitor Cp is connected to the output terminal of the operational amplifier A at the last stage of the series connection. However, since the output impedance of the operational amplifier A is originally low as described above, the pole generated by this output impedance and the feedback resistor R has a very high frequency. Therefore, the parasitic capacitance Cp connected to the output terminal of the operational amplifier A can be regarded as having no problem in practical use. As a result, one parasitic capacitance Cp
The above equation does not need to be considered, so that the return amplifier circuit has less change in the transfer function with respect to manufacturing variations.

[0048]

As is clear from the above, the integrated amplifier circuit according to the first aspect of the present invention has the number M of parallel circuits of the resistance element and the capacitance element constituting the negative feedback circuit, and connects the number of parallel circuits to the negative input terminal of the operational amplifier. Let the value of the resistor on the near side be R (N), the value of the capacitor be C (N), and the value of the resistor on the side closer to the output terminal of the operational amplifier be R (N + 1) Is C (N + 1), and the value of the parasitic capacitance that the capacitance element having the value C (N) has with the substrate is Cp (N), and 1 ≦ N
In the range of ≤ (M-1), the above values R (N) are set such that the equation C (N) ＮR (N) = {C (N + 1) + Cp (N)} ・ R (N + 1) holds. , C (N), R (N +
1) and C (N + 1), the parasitic capacitance (Cp
(N)) to prevent a pole from being generated in the transfer function of the feedback circuit, and the transfer function has τz = C (M) · R
Only the zero point represented by (M) can be generated.
Therefore, the advanced phase compensation function in the feedback circuit can be operated normally.

That is, according to the present invention, the shift of the transfer function of the phase compensation circuit due to the parasitic capacitance (Cp (N)) is eliminated, and the value of the transfer function is large enough so that the variation in manufacturing the integrated circuit does not matter. A feedback phase compensation capacitance element having a small value can be obtained by using the capacitance element, and wide band and high gain amplification can be performed.

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
If the values of the respective capacitance elements constituting the respective parallel circuits are all set to the same value, the shape of the respective capacitance elements is made the same, and the relative variation of the capacitance value in each of the capacitance elements occurring during manufacturing. Can be minimized. Therefore, it is possible to prevent the transfer function of the entire feedback circuit from changing due to manufacturing variations.

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
If the values of the respective resistance elements constituting the respective parallel circuits are all set to the same value, the shapes of the respective resistance elements are made the same, and the relative variation of the resistance values of the respective resistance elements generated during manufacturing is made. Can be minimized. Therefore, it is possible to prevent the transfer function of the entire feedback circuit from changing due to manufacturing variations.

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
If the number of parallel circuits constituting the negative feedback circuit and the time constant of each parallel circuit are set such that the value of the capacitance element constituting each parallel circuit is larger than the value of the parasitic capacitance of the capacitance element, Since the value of the capacitance element is larger than the parasitic capacitance, even when the matching between the capacitance element and the parasitic capacitance becomes poor, the time constant deviation in the corresponding parallel circuit can be reduced. Furthermore, the time constant difference between the right side and the left side in the case where the above equation is satisfied can be reduced, and the matching between the elements can be improved.

Further, the integrated amplifier circuit according to the first aspect of the present invention comprises:
If the capacitance element constituting each of the parallel circuits is connected with the terminal to which the parasitic capacitance is connected positioned closer to the output terminal of the operational amplifier, it is directly connected to the output terminal of the operational amplifier. The parasitic capacitance of the capacitive element can be directly connected to the output terminal of the operational amplifier having a low impedance. In that case, the poles generated by the output impedance and the M-th resistive element have a very high frequency, so that the above equation regarding the M-th parasitic capacitance does not need to be considered. That is, according to the present invention, the number of equations to be considered can be reduced.

Further, the integrated amplifier circuit according to the second aspect of the present invention calculates the values of each resistance element and each capacitance element of each parallel circuit constituting the negative feedback circuit and the number of the parallel circuits constituting the negative feedback circuit. If the transfer function of the loop composed of the amplifier and the negative feedback circuit is set so as to generate a predetermined number of poles and zeros of a predetermined frequency, another pole or zero other than the negative feedback circuit can be canceled or the integrated circuit can be integrated. It becomes possible to intentionally operate the frequency characteristics and the like of the amplifier circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a feedback amplifier circuit as an integrated amplifier circuit of the present invention.

FIG. 2 is a circuit diagram of a feedback amplifier circuit in which three parallel circuits of a feedback phase compensation capacitor and a feedback resistor in FIG. 1 are connected in series in three stages.

FIG. 3 is a circuit diagram of an inverting amplifier.

FIG. 4 is a cross-sectional view of a capacitor using a dielectric film.

FIG. 5 is a circuit diagram of a feedback amplifier circuit having a feedback circuit in which a plurality of capacitance elements are connected in series.

6 is an explanatory diagram of a parasitic capacitance attached to the capacitance in FIG.

[Explanation of symbols]

 PD11, PD21 ... photodiode, A11, A21 ... operational amplifier, R11, R12, R21, R22, R23 ... feedback resistor, C11, C12, C21, C22, C23 ... feedback phase compensation capacitance, Cp11, Cp12, Cp21, Cp22, Cp23: parasitic capacitance.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H03H 11/12 H03H 11/12 A F term (Reference) 5J090 AA01 CA01 CA18 CA26 FA17 FN10 HA01 HA25 HA29 HA44 MA13 MN02 NN02 SA13 TA01 TA02 5J091 AA01 CA01 CA18 CA26 FA17 HA25 HA29 HA44 MA13 SA13 TA01 TA02 5J092 AA01 CA01 CA18 CA26 FA17 HA25 HA29 HA44 MA13 SA13 TA01 TA02 UL02 5J098 AA06 AA11 AA14 AB02 AB03 AD03 AD26 CA02 CB06 CB06 CB08

Claims (6)

[Claims] An operational amplifier having at least two positive and negative input terminals; a negative feedback circuit connected between an output terminal and a negative input terminal of the operational amplifier;
An integrated integrated amplifier circuit, wherein the negative feedback circuit is configured by connecting a plurality of parallel circuits formed by connecting a resistance element and a capacitance element in parallel, in series. Let M be the number of parallel circuits to configure, and N
Is the number of the parallel circuit, and the value of the resistance element constituting the parallel circuit near the negative input terminal of the operational amplifier among any two parallel circuits connected in series is R (N)
On the other hand, the value of the capacitive element is C (N), the value of the resistive element constituting the parallel circuit near the output terminal of the operational amplifier is R (N + 1), and the value of the capacitive element is Is defined as C (N + 1), and the value of the parasitic capacitance between the substrate and the capacitance element having the diffusion-side capacitance electrode connected to the connection point of the four elements is defined as Cp (N), where 1 ≦ N ≦ (M -1), the values R (N), C (C (N), R (N) = {C (N + 1) + Cp (N)}. R (N + 1) are satisfied. N), R (N +
1) An integrated amplifier circuit, wherein C (N + 1) is set. 2. The integrated amplifier circuit according to claim 1, wherein all the values of the capacitance elements constituting each of the parallel circuits are set to the same value. 3. The integrated amplifier circuit according to claim 1, wherein all the values of the resistance elements constituting each of the parallel circuits are set to the same value. 4. The integrated amplifier circuit according to claim 1, wherein the number of the parallel circuits forming the negative feedback circuit and the time constant of each of the parallel circuits are determined by the value of the capacitance element forming each of the parallel circuits. An integrated amplifier circuit, which is set to be larger than a value of a parasitic capacitance of an element. 5. The integrated amplifier circuit according to claim 1, wherein a terminal of the capacitive element forming each of the parallel circuits to which a parasitic capacitance formed between the parallel circuit and the substrate is connected is higher than that of the other terminal. An integrated amplifier circuit, which is also connected to a side closer to an output terminal of the operational amplifier. 6. An operational amplifier having at least two positive and negative input terminals, a negative feedback circuit connected between an output terminal and a negative input terminal of the operational amplifier,
An integrated integrated amplifier circuit, wherein the negative feedback circuit is configured by connecting a plurality of parallel circuits in which a resistance element and a capacitance element are connected in parallel, and is connected in series. The value of each capacitive element and the number of parallel circuits constituting the negative feedback circuit were set so as to generate a predetermined number of poles and zeros of a predetermined frequency in a transfer function of a loop including the operational amplifier and the negative feedback circuit. An integrated amplifier circuit characterized in that: