JPH0998030A - Semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate amplification factor variation within the range that is caused by the influence of the anti-semiconductor substrate parasitic elements existing in a transistor when a semiconductor integrated circuit is produced for construction of a feedback amplifier. SOLUTION: A resistor Rx and a capacitor Cx construct a feedback circuit FC having the same frequency characteristic as that of the parallel impedance set between the anti-semiconductor substrate parasitic elements (substrate resistance Rs, substrate capacity Cs and collector-substrate capacity Cts) and the impedance load (load resistance RL) exisien in a transistor Q. The resistor Rx and the capacitor Cx are mounted on a semiconductor substrate, so that they are connected in parallel to a feedback resistor RE of a feedback amplifier. In such a constitution, the frequency characteristic due to the anti-semiconductor substrate parasitic elements is compensated by the circuit FC. Thus it is possible to prevent the deterioration of amplification factor G even in the intermediate frequency band MB that exceeds the intermediate frequency of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, and more particularly, when a feedback amplifier is composed of a plurality of circuit elements including transistors formed on a semiconductor substrate,
The present invention relates to a technique effectively applied to a semiconductor integrated circuit for preventing the influence of a parasitic element with respect to a semiconductor substrate which is inherent in a transistor.

[0002]

2. Description of the Related Art Recently, an LS used particularly in an ultra high frequency range
The demand for I is increasing. This ultra-high-frequency LSI is, for example, 10 (Gbit / s) like baseband optical communication.
It is used when constructing a broadband amplifier for optical transmission that requires a high transmission rate.

When such an LSI is manufactured using a Si substrate that is generally widely used, the Si substrate has a smaller resistance value than an insulator, so that a substrate resistance Rs and a substrate capacitance Cs are formed as parasitic elements. As a result, a parallel circuit of the substrate resistance Rs and the substrate capacitance Cs is equivalently formed. For example, ISSCC DIGE
ST OF TECHNICAL PAPERS, pp
202-203, Feb. 1992 shows a Si substrate in which a parallel circuit of the substrate resistance Rs and the substrate capacitance Cs is modeled in this way.

When, for example, a bipolar transistor (hereinafter simply referred to as a transistor) is formed on the Si substrate, a collector-substrate capacitance Cts is formed as another parasitic element between the Si substrate and the collector. .
Therefore, if a transistor is formed on the Si substrate,
A parasitic element with respect to the semiconductor substrate, which is composed of the substrate resistance Rs, the substrate capacitance Cs, and the collector-substrate capacitance Cts, is formed, and these parasitic elements are inherent in the transistor.

Therefore, a semiconductor integrated circuit in which a load resistor RL is formed as an impedance load so as to be connected to a transistor and its collector on a Si substrate and a feedback resistor RE is formed so as to be connected to its emitter is manufactured. Assuming that a grounded-emitter-type emitter feedback amplifier is configured, the impedance load of the transistor of this feedback amplifier is affected by the parasitic element to the semiconductor substrate, and circuit elements other than the load resistance RL are connected. That is, in the equivalent circuit of the feedback amplifier in this case, the collector-substrate capacitance Cts is connected in series to the parallel circuit of the substrate resistance Rs and the substrate capacitance Cs as described above, and this series circuit is parallel to the load resistor RL. It becomes the form connected to.

As described above, when another circuit element is connected in parallel to the load resistor RL, the impedance load changes according to the frequency of the signal, and the amplification factor of the feedback amplifier has frequency dependency. Become.

Since the amplification factor of the feedback amplifier is determined by the ratio of the impedance load (load resistance RL) and the feedback resistance RE (load resistance RL / feedback resistance RE), a flat amplification factor can be expected over a wide band. It is preferably used in wide band amplifiers such as the base band optical communication described above.

In general, the substrate resistance Rs is sufficiently larger than the load resistance RL (Rs >> RL), and the separation capacitance Cts is sufficiently larger than the substrate capacitance Cs (Cts >> C).
s).

[0009]

When the impedance load of the transistor forming the feedback amplifier is affected by the parasitic element on the semiconductor substrate other than the load resistance RL as described above, the amplification factor of the feedback amplifier vs. frequency. In the frequency characteristics showing the relationship, the amplification factor becomes frequency dependent, and in particular, the amplification factor in the intermediate frequency band becomes lower than the amplification factor in the low frequency band. There is a problem that occurs.

In this way, when an in-band deviation of the amplification factor occurs, in a system using a feedback amplifier as a wide band amplifier, a change in the amplification factor appears as it is as a deterioration of the transmission characteristic, so that information is transmitted accurately and at high speed. It will cause problems in the above.

The reason why the in-band deviation of the amplification factor occurs will be described in more detail. In the frequency characteristic showing the relationship between the amplification factor and the frequency, since the impedance load is hardly affected by the parasitic element on the semiconductor substrate in the low frequency band, almost only the load resistance RL is set.
/ RE).

Next, in the intermediate frequency band exceeding the intermediate frequency fo represented by 1 / (2π · Rs · Cts), there is almost no influence of the substrate capacitance Cs, and the collector-substrate capacitance C
Since ts appears to be short-circuited, the impedance load is a parallel combined resistance of the load resistance RL and the substrate resistance Rs {(RL
・ Rs) / (RL + Rs)}. Therefore, the amplification factor is given by (RL / RE) · {Rs / (RL + Rs)}. Furthermore, in the high frequency band, the substrate capacitance Cs and the base-collector capacitance Ctc appear to be short-circuited,
The amplification factor approaches 0.

Therefore, in the frequency characteristic showing the relationship between the amplification factor and the frequency, the amplification factor (RL / RE) in the low frequency band is obtained.
And the amplification factor (RL / RE) · {Rs / (RL + Rs)} of the intermediate frequency band that exceeds the intermediate frequency fo, it is clear that the amplification factor of the intermediate frequency band is lower than that of the low frequency band. Since it also decreases, in-band deviation of the amplification factor cannot be avoided. Therefore, a flat amplification factor cannot be obtained over a wide band.

An object of the present invention is, when manufacturing a semiconductor integrated circuit forming a feedback amplifier, a technique capable of eliminating an in-band deviation of an amplification factor caused by an influence of a parasitic element with respect to a semiconductor substrate existing in a transistor. To provide.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0016]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, typical ones are briefly described as follows.

In the semiconductor integrated circuit of the present invention, a feedback amplifier is constituted by a plurality of circuit elements including a transistor for amplifying and outputting an input signal and an impedance load connected to the output side of the transistor, and the plurality of circuit elements are provided. Is a semiconductor integrated circuit formed on a common semiconductor substrate, and has a frequency characteristic of the parallel impedance of the parasitic element to the semiconductor substrate and the impedance load, which is inherent in the transistor, and has the same frequency characteristic as the feedback characteristic. A circuit element forming a circuit is formed on the semiconductor substrate so as to be connected to a desired position of the feedback amplifier.

According to the above-mentioned means, the semiconductor integrated circuit of the present invention has the parallel impedance of the parasitic element to the semiconductor substrate existing in the transistor formed on the semiconductor substrate and the impedance load connected to the output side of the transistor. As for the frequency characteristic, the circuit element forming the feedback circuit having the same frequency characteristic as this is formed on the semiconductor substrate so as to be connected to the desired position of the feedback amplifier. The frequency characteristic is compensated by the circuit element that constitutes the feedback circuit. Therefore, when manufacturing a semiconductor integrated circuit that constitutes a feedback amplifier, it is possible to eliminate the in-band deviation of the amplification factor caused by the influence of the parasitic element with respect to the semiconductor substrate existing in the transistor.

Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments.

In all the drawings for describing the embodiments, parts having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

[0021]

1 is a plan view showing a semiconductor integrated circuit according to an embodiment of the present invention, in which a load resistor RL is formed as an impedance load on a semiconductor substrate so as to be connected to, for example, a bipolar transistor and its collector, and This is an example in which a semiconductor integrated circuit in which a feedback resistor RE is formed so as to be connected to the emitter is manufactured to form a grounded-emitter type emitter feedback amplifier. 2 is a sectional view taken along the line AA of FIG. 1, FIG. 3 is a sectional view taken along the line BB of FIG. 1, and FIG. 4 shows an equivalent circuit of a feedback amplifier configured by the semiconductor integrated circuit of this embodiment. It should be noted that the pattern of each component in FIG. 1 is an example for simplifying the description, and can be arbitrarily changed in the actual manufacture of the semiconductor integrated circuit.

In the semiconductor integrated circuit 1 of the present embodiment, a plurality of N-type regions 3A, 3B, 3C ... Insulated and separated from each other are formed on a semiconductor substrate 2 made of, for example, a P-type silicon single crystal substrate, and each region is formed. The desired element is formed as follows.

In one N-type region 3B, for example, an NPN-type bipolar transistor (hereinafter, simply referred to as transistor) Q which functions as an active element is formed. 4 is N
+ Type buried layer, 5 N type collector region, 6 P type base region, 7 N + type emitter region, 8 N + type collector contact region, 9 collector electrode layer, 10 base electrode layer, 11 emitter Electrode layer, 12 is an oxide film (SiO ₂ )
It is an insulating film made of, for example, surface protection. An Al alloy or the like is used for each electrode.

The P-type region 14 is formed in the other N-type region 3A.
Is formed, and the end of the P-type region 13 is formed by the transistor Q.
And is used as a load resistance RL.

Further, a P-type region 15 is formed in the other N-type region 3C, and this P-type region 15 is formed by the transistor Q.
And is used as a feedback resistor RE.

In the above, each region 4, 5, 6, 7,
As a means for forming 8, 14, and 15, a well-known impurity ion implantation method, diffusion method, epitaxial method, or the like can be used. In addition, the load resistance RL and the feedback resistance R
The value of E can be obtained at an almost arbitrary value by adjusting the impurity concentrations of the P-type region 14 forming each resistance and the P-type region 15 forming the feedback resistor RE. Here, the configuration of each of the resistors RL and RE is an example, and various resistance films are formed on the insulating film 12 without forming the P-type regions 14 and 15 in each of the N-type regions 3A and 3C. It can also be configured. For these resistance films, for example, well-known high melting point materials such as polycrystalline Si, W, Mo, Ti, and Ta can be used.

As shown in FIG. 3, a part 12A of the insulating film 12 of the semiconductor substrate 2 adjacent to the N-type region 3A is thinly formed, and the wiring 16 is formed on the insulating thin film 12A, and An N + region 17 is formed on the semiconductor substrate 2 just below the insulating thin film 12A. Insulating thin film 1
Wiring 16 and N + region 1 as a conductive layer above and below 2A
By forming 7, the capacitance Cx is formed. The wiring 16 is led out from the other end of the P-type region 15 which constitutes the load resistance RL.

A resistance film 19 made of a high melting point material such as polycrystalline Si or W, Mo, Ti, Ta or the like is drawn out onto the insulating film 12 so as to come into contact with the end of the N + region 17 through the contact hole 18. Are formed, thereby forming the resistance Rx. The resistance film 19 is connected to the emitter electrode layer 11 of the transistor Q. As a result, the resistor Rx and the capacitor Cx are connected in series, and this series circuit is connected in parallel with the feedback resistor RE. The series circuit of the resistor Rx and the capacitor Cx acts as a feedback circuit FC for preventing the decrease of the amplification factor in the intermediate frequency band exceeding the intermediate frequency fo, as described later.

As described above, an emitter feedback amplifier having an equivalent circuit as shown in FIG. 4 is constructed. here,
The values of the capacitance Cx and the resistance Rx are set as described later.

Next, the principle of the present invention will be described. In the feedback amplifier, the substrate capacitance Cs and the base-collector capacitance Ctc have almost no influence in the intermediate frequency band exceeding the intermediate frequency fo in which the in-band deviation of the amplification factor occurs. Therefore, ignoring this,
The impedance load of the transistor Q is, as shown in FIG. 5, a substrate resistance Rs and a collector resistance with respect to a load resistance RL.
A series circuit with the inter-substrate capacitance Cts is a parallel circuit connected in parallel.

Here, assuming that the imaginary unit is j, the amplification factor is proportional to the following equation in the intermediate frequency band over the intermediate frequency fo = (1 / 2π · Rs · Cts).

[0032]

## EQU00001 ## {1-j (fo / f)} / (RL / Rs) + {1-j (fo / f)}, where f is the frequency of the signal.

The above formula is derived based on FIG. Now, when the combined resistance of the parallel circuit of FIG. 5 is represented by Rt, this combined resistance Rt is expressed by the following equation.

[0034]

## EQU00002 ## Rt = RL.multidot. {Rs + (1 / j.omega.Cts)} / RL + {Rs + (1 / j.omega.Cts)} = RL.Rs {1+ (1 / j.omega.RsCts)} / RL.Rs {1+ (1 / j.omega.RsCts)} (∵ω = 2πf) Here, if Rs · Cts = 1 / 2πfo and 1 / j = −j,

[0035]

## EQU00003 ## Rt = RL.Rs {1-j (fo / f)} / RL + Rs {1-j (fo / f)} = RL {1-j (fo / f) / (RL / Rs) + { 1-j (fo / f)} = RL.multidot. {1-j (fo / f)} / (RL / Rs) + {1-j (fo / f)} ... That is, the combined resistance Rt is proportional to the above equation. Will be done. In the equation, the amplification factor at DC is RL / RE.
Therefore, RL is shown separately.

Therefore, if a feedback amplifier is constructed by connecting a feedback circuit having a feedback amount showing a frequency characteristic inversely proportional to the frequency characteristic of the equation, the influence of the parasitic element to the semiconductor substrate can be prevented and the intermediate frequency fo It is possible to prevent a decrease in the amplification factor that occurs in an intermediate frequency band that exceeds.

From the above viewpoint, in the present embodiment,
In order to make the series circuit of the resistor Rx and the capacitor Cx connected in parallel to the feedback resistor RE act as the feedback circuit as described above, the resistor Rx and the capacitor Cx are set as follows.

[0038]

## EQU00004 ## Rx = Rs.RE / RL ...

[0039]

## EQU00005 ## Cx = Rs.Cts / Rx ... Next, the operation of the present embodiment will be described.

In the frequency characteristic showing the relationship between the amplification factor G (vertical axis) and the frequency f (horizontal axis) as shown in FIG. 6, the impedance load is hardly affected by the parasitic element on the semiconductor substrate in the low frequency band LB. Since the resistance Rx and the capacitance Cx can be ignored in the equivalent circuit of FIG. 4,
The amplification factor G is (RL /
RE).

Next, the intermediate frequency fo = 1 / (2πRsC, which appears when the collector-substrate capacitance Cts is short-circuited
In the intermediate frequency band MB exceeding ts), the impedance load is the parallel combined resistance Rk of the load resistance RL and the substrate resistance Rs as shown by the following equation.

[0042]

## EQU00006 ## Rk = (RL.Rs) / (RL + Rs) ... Further, from the setting of the above equation, in the intermediate frequency band MB, the feedback resistance of the transistor Q is not RE but the feedback resistance R.
Combined resistance value of E and resistance Rx (RE ・ Rx / RE + R
s). Now, if this is shown by the feedback combined resistance Rg,
This feedback combined resistance Rg is expressed by the following equation.

[0043]

[Equation 7] Rg = (RE · Rx) / (RE + Rx) = RE · (Rs · RE / RL) / RE + (Rs · RE / RL) = (RE 2 · Rs) / RL {RE + (Rs · RE / RL)} = (RE ² · Rs) / RL · RE {1+ (Rs / RL)} = (RE · Rs) / RL {1+ (Rs / RL)} = (RE · Rs) / (RL + Rs) , The amplification factor G in the intermediate frequency band MB is the impedance load (parallel combined resistance Rk) / feedback combined resistance R
g = equation / equation, which is shown by the following equation.

[0044]

## EQU00008 ## Amplification factor G = {(RL.Rs) / (RL + Rs)} / {(RE.Rs) / (RL + Rs)} = RL / {1+ (RL / Rs)} / RE.Rs/(RL+Rs) = RL {1+ (RL / Rs)} / = RE {(RL / Rs) +1} = (RL / RE) * {1+ (RL / Rs)} / {1+ (RL / Rs)} = RL / RE ... As is clear from this formula, according to the present embodiment,
By connecting the feedback circuit FC composed of the resistor Rx and the capacitor Cx set so as to satisfy the equation and the equation in parallel to the feedback resistor RE, even in the intermediate frequency band MB exceeding the intermediate frequency fo, the low frequency band LB It becomes possible to obtain the same gain G as the gain G in.

That is, in the present embodiment, a feedback circuit FC having a feedback amount exhibiting a frequency characteristic inversely proportional to the frequency characteristic of the above equation is connected in parallel to the feedback resistor RE to form a feedback amplifier. Therefore, the frequency characteristic caused by the parasitic element with respect to the semiconductor substrate is compensated by the resistance Rx and the capacitance Cx which form the feedback circuit FC. Therefore, as shown in FIG. 6, a flat amplification factor can be obtained over a wide band from the low frequency band LB to the intermediate frequency band MB.

The characteristic of the broken line in FIG. 6 shows the conventional example, and the intermediate frequency band M exceeding the intermediate frequency fo is shown.
A value (RL / RE) in which the amplification factor G in B is proportional to an impedance load formed by a parallel combined resistance {(RL · Rs) / (RL + Rs)} of the load resistance RL and the substrate resistance Rs.
・ {Rs / (RL + Rs)} is shown, which shows a decrease.

According to this embodiment, the following effects can be obtained.

A parasitic element to the semiconductor substrate (substrate resistance Rs, substrate capacitance Cs and collector.
Inter-board capacitance Cts) and impedance load (load resistance R
With respect to the frequency characteristic of the parallel impedance with L), the semiconductor substrate 2 is configured such that the resistor Rx and the capacitor Cx forming the feedback circuit FC having the same frequency characteristic as that of the parallel impedance are connected in parallel to the feedback resistor RE of the feedback amplifier. Therefore, it is possible to prevent the amplification factor G from decreasing even in the intermediate frequency band MB that exceeds the intermediate frequency fo. Therefore,
When manufacturing a semiconductor integrated circuit that constitutes a feedback amplifier,
It is possible to eliminate the in-band deviation of the amplification factor caused by the influence of the parasitic element with respect to the semiconductor substrate, which is inherent in the transistor Q.

The inventions made by the present inventors are as follows.
Although specifically described based on the embodiment, the present invention
It is needless to say that the present invention is not limited to the above embodiment, and various changes can be made without departing from the scope of the invention.

For example, in the above-described embodiment, an example has been described in which the feedback circuit for compensating the frequency characteristic caused by the parasitic element to the semiconductor substrate is connected in parallel with the feedback resistor, but the present invention is not limited to this, and the feedback circuit may be a desired feedback amplifier. It can be configured to be connected in position. It suffices if the connection relationship is such that feedback is applied to the feedback amplifier.

Further, although the emitter feedback amplifier has been described as an example, the present invention is not limited to this and can be applied to any type of feedback amplifier. Further, the configuration of the amplifier itself is not limited to the example of the embodiment, and other configurations such as a differential amplifier can be adopted.

Furthermore, in the above-described embodiment, an example in which a bipolar transistor is formed as an active element forming a feedback amplifier has been described, but the present invention is not limited to this, and a MOS transistor may be formed.

Further, the configuration of the resistance and the capacitance constituting the feedback circuit is an example, and other configurations can be selected by applying a well-known process technique.

In the above description, the case where the invention made by the present inventor is mainly applied to the technology of the semiconductor integrated circuit which is the background field of application has been described, but the invention is not limited thereto. The present invention can be applied at least under the condition of forming a circuit element that operates without being affected by the parasitic element with respect to the semiconductor substrate.

[0055]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

With respect to the frequency characteristic of the parallel impedance of the parasitic element to the semiconductor substrate and the impedance load, which is inherent in the transistor, the circuit element constituting the feedback circuit having the same frequency characteristic is connected to the desired position of the feedback amplifier. Since it is formed on the semiconductor substrate as described above, when manufacturing a semiconductor integrated circuit forming a feedback amplifier, an in-band deviation of the amplification factor caused by the influence of the parasitic element with respect to the semiconductor substrate existing in the transistor Q is eliminated. It becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor integrated circuit according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is an equivalent circuit of a feedback amplifier configured by the semiconductor integrated circuit according to the embodiment of the present invention.

FIG. 5 is an equivalent circuit illustrating the principle of the present invention.

FIG. 6 is a frequency characteristic showing the relationship between the amplification factor and the frequency, which is obtained by the feedback amplifier configured by the semiconductor integrated circuit according to the embodiment of the present invention.

[Explanation of symbols]

1 ... Semiconductor integrated circuit, 2 ... Semiconductor substrate, 3, 3A, 3
B, 3C ... N type region, 4 ... N + type buried layer, 5 ... N type collector region, 6 ... P type base region, 7 ... N + type emitter region, 8 ... N + type collector contact region, 9 ... Collector electrode layer 10 ... Base electrode layer, 11 ... Emitter electrode layer,
12 ... Insulating film, 12A ... Insulating thin film, 14, 15 ... P type region, 16 ... Wiring, 17 ... N + type region, 18 ... Contact hole, 19 ... Resistive film, Rs ... Substrate resistance, Cs ... Substrate capacitance, Cts ... Collector-substrate capacitance, Q ... Transistor, RL ... Load resistance, RE ... Feedback resistance, FC ... Feedback circuit, Rx ... Resistance, Cx ... Capacitance, Ctc ... Base-collector capacitance.

Claims (6)

[Claims] 1. A feedback amplifier is constituted by a plurality of circuit elements including a transistor for amplifying and outputting an input signal and an impedance load connected to the output side of the transistor, and the plurality of circuit elements are formed on a common semiconductor substrate. A semiconductor integrated circuit to be formed, which constitutes a feedback circuit having the same frequency characteristic as the frequency characteristic of the parallel impedance of the parasitic element with respect to the semiconductor substrate existing in the transistor and the impedance load. Is formed on the semiconductor substrate so as to be connected to a desired position of the feedback amplifier. 2. The feedback resistor of the feedback amplifier is formed on the semiconductor substrate, and the circuit element forming the feedback circuit is formed so as to be connected in parallel to the feedback resistor. The semiconductor integrated circuit according to 1. 3. The circuit element forming the feedback circuit is set to the same time constant as the time constant set by the parasitic element to the semiconductor substrate in the transistor. The semiconductor integrated circuit according to 1. 4. The semiconductor integrated circuit according to claim 1, wherein the circuit element forming the feedback circuit comprises a series circuit of a resistor Rx and a capacitor Cx. 5. The resistor Rx is Rx = Rs.RE / R.
5. The semiconductor integrated circuit according to claim 4, wherein the semiconductor integrated circuit is set to satisfy L (where Rs: substrate resistance, RE: feedback resistance, RL: load resistance). 6. The capacitance Cx is Cx = Rs · Cts /
5. The semiconductor integrated circuit according to claim 4, wherein Rx (where Rs: substrate resistance, Cts: collector-substrate capacitance, Rx: resistance) is set.