JPH07193189A - Analog/digital lsd - Google Patents

Abstract

PURPOSE:To reduce the effects of noise appearing from digital circuits having no dedicated power wiring to board connection by providing digital circuits having dedicated power wirings to board connection around analog circuits. CONSTITUTION:An analog/digital LSD 4 comprises an analog circuit 1, a digital circuit 2 with a power wiring dedicated to circuit board connection, and a digital circuit 3 without a power wiring. If a digital cell having a power wiring dedicated to board connection, which may be provided according to a user' requirement, is arranged between existing digital cells and analog cells, an analog/digital LSD of low noise can be realized without additional cells. Therefore, the number of steps for a LSD development is decreased and the increase in chip area is minimized to reduce the effects of noise appearing from digital circuits.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog / digital mixed LSI in which a digital circuit such as a gate array is equipped with an analog circuit such as an A / D converter, and its configuration.

[0002]

2. Description of the Related Art When constructing a mixed LSI in which an analog circuit is mounted together with a digital circuit, there is a problem that noise generated by the digital circuit affects the analog circuit through the substrate of the LSI. Methods for reducing digital noise or substrate noise are being studied.
A method of generating and reducing substrate noise will be described by taking an inverter of a digital circuit as an example. 14 and 15 show C composed of p-channel and n-channel MOS transistors.
A MOS inverter is shown. Conventionally, as shown in FIG.
The third terminal 24 and the fourth terminal 25 of the channel MOS transistor are connected inside the chip 28, and the ground terminal 2
It was output as 6. However, in this connection, digital noise is usually generated at the third terminal 24 along with the operating current of the CMOS inverter, and this noise is directly transmitted to the fourth terminal 25, resulting in noise on the substrate voltage of the chip. In order to reduce this substrate noise, it is necessary to separate the fourth terminal 25 of the n-channel MOS transistor to make it less susceptible to noise. Therefore, it is generally known that it is effective to reduce the substrate noise by outputting the fourth terminal 25 as a substrate contact terminal 27 to the outside of the chip and directly applying a stable voltage to the substrate as shown in FIG. ing. The technique of providing the connection terminal only for the substrate contact in this way is described in JP-A-54-9322.

[0003]

Although it is possible to reduce the influence of digital noise on the analog circuit by providing a connection terminal dedicated to the substrate contact, in this case, the chip area increases during layout. There is. Further, most of conventional cell libraries of digital circuits are mainly used for digital LSIs and do not have power supply wiring dedicated to substrate contacts, and are not suitable for mixed analog / digital LSIs. However, a great deal of work is required to replace all of these cells with new cells having power wiring dedicated to substrate contacts. In this way, when actually constructing an analog / digital circuit mixed LSI, it is necessary to reduce the development man-hours by limiting the chip area or effectively using the cell library. It is impossible to reduce the noise by providing the power supply wiring dedicated to the substrate contact.

[0004]

In order to solve the above problems, in an analog / digital mixed LSI, a digital circuit having no dedicated power supply wiring for board contact is arranged apart from the analog circuit, and a board is provided near the analog circuit. Place a digital circuit with dedicated power wiring for contacts.

[0005]

In the analog / digital mixed LSI, the effectiveness of providing the wiring dedicated to the substrate contact is shown as follows from the result of the preliminary experiment. FIG. 16 shows the configuration of the analog / digital mixed LSI used in the preliminary experiment. Evaluation analog / digital mixed LSI 31
Is composed of a digital circuit 32 used as a noise source and an analog circuit 33 used as a detection circuit.
FIG. 17 is a result of measuring the effect of the power supply wiring dedicated to the board ground by the evaluation analog / digital mixed LSI 31. It is shown that the measurement result 35 when the power supply wiring dedicated to the substrate contact is used is reduced to about 1/3 of the noise as compared with the measurement result 36 when the power supply wiring dedicated to the substrate contact is not provided. From this result, it is clear that the influence of noise on the analog circuit can be reduced by the digital circuit having the power supply wiring dedicated to the substrate contact. Therefore,
Analog circuits of noise generated by digital circuits also when a digital circuit that does not have a dedicated power supply wiring for board contact is placed away from an analog circuit and a digital circuit that has a dedicated power supply wiring for board contact is placed near the analog circuit. Can be reduced.

[0006]

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

A first embodiment of the present invention will be described with reference to FIG. Mixed analog / digital LSI according to the present invention
Reference numeral 4 is composed of an analog circuit 1, a digital circuit 2 having a power supply wiring dedicated to the substrate contact, and a digital circuit 3 having no power wiring dedicated to the substrate contact. Here, the analog circuit is a circuit that handles continuously changing signals, such as an amplifier and an analog / digital converter. On the other hand, there are many digital cells already built in the digital circuit, such as a microcomputer. For example, in the case of constructing an application specific integrated circuit (ASIC), it suffices to arrange a digital cell having a power supply wiring for exclusive use of substrate contact, which is created according to a user's need, between an existing digital cell and an analog circuit. As a result, analog / noise that reduces the effect of noise without newly creating unnecessary cells
A digital mixed LSI can be constructed. In this way, the digital circuit 2 having the power supply wiring dedicated to the substrate contact
Is placed around the analog circuit, it is possible to reduce the influence of noise generated by the digital circuit having no dedicated power supply wiring for the substrate contact on the analog circuit by being transmitted through the LSI substrate.

A second embodiment of the present invention is shown in FIG. In general, the scale of an analog circuit in an analog / digital mixed LSI is smaller than that of a digital circuit. Therefore, if a square LSI as shown in the figure is considered, the analog circuit 1 can be installed in one corner. As a result, the wiring for exchanging signals with the outside of the LSI can be shortened. Also, when it is necessary to newly lay out a digital circuit having a power supply wiring dedicated to the substrate contact, it is not necessary to surround the four sides of the analog circuit, so that the cell size can be reduced and the development man-hour can be reduced. Is. Further, when there are two blocks of analog circuits, such as an analog / digital converter and a digital / analog converter, the analog circuits are installed in two corners, such as 1a and 1b, as shown in FIG. Then, it is possible to arrange the digital circuit 2 having a power supply wiring dedicated to the substrate contact around it to reduce noise. It is also possible to arrange the digital circuit having the power wiring for exclusive use of the substrate contact as shown in FIGS. 4 and 5 according to the circuit scale of the digital circuit having no power wiring for the exclusive use of substrate contact (for example, the inverter of FIG. 15). is there. Also, there is a shortage of cells that have power supply wiring dedicated to board contacts,
When the analog circuit cannot be enclosed, it is possible to arrange and supplement the power supply wiring region dedicated to the substrate contact.

In the above embodiment, it is assumed that a digital circuit is installed around the analog circuit, but in reality, signals are exchanged between the analog circuit and the digital circuit. In this case, noise generated by a digital circuit that receives a signal from the analog circuit or transmits a signal to the analog circuit easily affects the operation of the analog circuit. A third embodiment of the present invention for solving this problem is shown in FIG. In FIG. 6, the analog / digital mixed LSI 4 inputs the analog input signal V1 and outputs the digital output signal V2. Here, the analog circuit 1 is connected to a digital circuit 2 having a power supply wiring dedicated to substrate contacts, and the signal thereof is connected to a digital circuit 3 having no power wiring dedicated to substrate contacts. As a result, it is possible to reduce the influence of noise generated from the digital circuit connected to the analog circuit. In addition, as shown in FIG.
3 and outputs the analog signal V4,
As shown in FIG. 4, when the analog signal V5 is received, the digital signal processing is performed, and the analog signal V6 is output again, the digital circuit for exchanging signals with the analog circuits 1c and 1d is similarly connected to the power supply wiring dedicated to the substrate contact. Noise can be reduced by using the digital circuits 2a and 2b.

In order to suppress the influence of digital noise, it is effective to dispose a guard band which is an electrode for suppressing the fluctuation of the substrate potential. A fourth embodiment of the present invention for that purpose is shown in FIG. A guard band 5 is installed between the analog circuit 1 and the digital circuit 2 having the power supply wiring dedicated to the substrate contact. As a result, it becomes possible to stabilize the substrate potential and suppress the transmission of noise. Further, as shown in FIG. 10, by providing the guard band 5b between the digital circuit 2 having the power supply wiring dedicated to the substrate contact and the digital circuit 3 not having the power wiring dedicated to the substrate contact (for example, FIG. 15), noise is further reduced. It is possible to reduce the influence on the analog circuit.

Next, FIG. 11 shows a fifth embodiment of the present invention relating to the wiring of the power source for realizing the above embodiment.
In the present embodiment, the analog circuit 1 power supply, ground,
Substrate contacts are AVDD, AVSS, AVB respectively
The power source and the ground of the digital circuit 2 having the power supply wiring dedicated to the substrate contact are connected to the terminal B, and the power source of the digital circuit 3 having no board contact is connected to the DVDD2, DVSS2 and DVBB2 terminals, respectively.
The grounds are connected outside the chip by the terminals of DVDD1 and DVSS1, respectively. Here, the power supplies AVDD, D
VDD1, DVDD2 and ground DVSS1, DV
SS2, DVBB2, AVSS, and AVBB can be shared and supplied outside the chip.

However, when the power supply terminal and the ground terminal are respectively connected outside the chip, there is a problem that the number of terminals increases. Therefore, as shown in FIG. 12, the power supplies of the digital circuit 2 having the power supply wiring dedicated to the substrate contact and the digital circuit 3 having no power supply wiring dedicated to the substrate contact are set to D.
The common use as VDD can reduce the number of terminals of the chip. Similarly, the ground DVSS can be shared, and the number of power supply lines of the digital circuit can be reduced from five to three. Also, as shown in FIG.
It is also possible to reduce the number of terminals of the power supply line by making the DVBB2 and DVBB2 common to form one terminal AVBB.

The first, second, third, fourth and fifth embodiments described above can be implemented in combination.

[0014]

EFFECTS OF THE INVENTION By arranging a digital circuit having no power supply wiring for exclusive use of substrate contact away from the analog circuit and arranging a digital circuit having power supply wiring for exclusive use of substrate contact in the vicinity of the analog circuit, the number of LSI development steps can be suppressed. Moreover, the influence of noise generated in the digital circuit can be reduced with the minimum increase in the chip area. As a result, large-scale analog / digital mixed L equipped with analog circuits
SI can be constructed.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram 1 showing a second embodiment of the present invention.

FIG. 3 is a diagram 2 showing a second embodiment of the present invention.

FIG. 4 is a diagram 3 showing a second embodiment of the present invention.

FIG. 5 is a diagram 4 showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram 2 showing a third embodiment of the present invention.

FIG. 8 is a diagram 3 showing a third embodiment of the present invention.

FIG. 9 is a diagram 1 showing a fourth embodiment of the present invention.

FIG. 10 is a second diagram showing the fourth embodiment of the present invention.

FIG. 11 is a diagram showing a fifth embodiment of the present invention.

FIG. 12 is a diagram 2 showing a fifth embodiment of the present invention.

FIG. 13 is a view 3 of the fifth embodiment of the present invention.

FIG. 14 is a diagram illustrating power supply connection of an inverter circuit that does not have a power supply wiring dedicated to substrate contacts.

FIG. 15 is a diagram illustrating power supply connection of an inverter circuit having a power supply wiring dedicated to substrate contacts.

FIG. 16 is a diagram for explaining the configuration of an analog / digital mixed LSI for noise measurement preliminary experiments.

FIG. 17 is a diagram showing a measurement result of a noise reduction effect by a digital circuit having a power supply wiring dedicated to a substrate contact.

[Explanation of symbols]

1, 1a, 1b, 1c, 1d ... Analog circuits, 2, 2
a, 2b ... Digital circuit having dedicated power supply for substrate contact, 3 ... Digital circuit not having dedicated power supply wiring for substrate contact, 4 ... Analog / digital mixed LSI, 5, 5
a, 5b ... Guard band, 21 ... Input terminal, 22 ... Output terminal, 23 ... Power supply terminal, 24 ... N-channel MOS transistor third terminal, 25 ... N-channel MOS transistor fourth terminal, 26 ... Ground terminal, 27 ... Substrate Dedicated contact terminal, 31 ... Analog / digital mixed LS for evaluation
I, 32 ... Digital circuit, 33 ... Analog circuit, 35 ...
The measurement result of the digital circuit having the power supply wiring dedicated to the board contact, 36 ...

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuharu Matsuura 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (9)

[Claims] Claim: What is claimed is: 1. An analog / digital mixed LSI comprising an analog circuit, a digital circuit having board-dedicated power supply wiring, and a digital circuit having no board-contact dedicated power supply wiring. An analog / digital mixed LSI characterized in that a digital circuit having a power supply wiring dedicated to a substrate contact is arranged in the vicinity of the analog circuit and is arranged apart from the analog circuit. 2. The analog / digital mixed LSI according to claim 1, wherein the analog circuit is surrounded by a digital circuit having a power supply wiring dedicated to substrate contact. 3. The analog / digital mixed LSI according to claim 1, wherein the analog circuit is arranged in a peripheral portion of the LSI. 4. The analog / digital mixed LSI according to claim 1, claim 2, or claim 3, wherein the analog circuit is electrically connected to a digital circuit having a power supply wiring dedicated to substrate contacts. Method of configuring analog / digital mixed LSI. 5. Claim 1, claim 2, claim 3, claim 4
In the analog / digital mixed LSI described in the item 1, the analog / digital mixed LS is characterized in that a guard band for suppressing fluctuation of the substrate potential is arranged between the analog circuit and the digital circuit having the power supply wiring dedicated to the substrate contact.
I. 6. The analog / digital mixed LSI according to claim 1, claim 2, claim 3, claim 4 or claim 5, wherein a digital circuit having a power supply wiring dedicated to substrate contact and a power supply wiring dedicated to substrate contact are provided. A mixed analog / digital LS characterized by arranging a guard band for suppressing substrate potential fluctuation between digital circuits that do not have
I. 7. The analog / digital mixed LSI according to claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6, wherein a digital circuit having a power supply wiring dedicated to the board contact and the board contact are provided. Analog / digital mixed L characterized by separating the power supply and ground of a digital circuit that does not have a dedicated power supply wiring and connecting to the chip terminal
SI. 8. The analog / digital mixed LSI according to claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6, wherein a digital circuit having a power supply wiring dedicated to the board contact and the board contact are provided. An analog / digital mixed LSI characterized in that the power supply and ground of a digital circuit having no dedicated power supply wiring are made common and connected to the power supply and ground terminals of a chip. 9. The analog / digital mixed LSI according to claim 1, claim 2, claim 3, claim 4, claim 5, and claim 6, wherein a substrate contact of a digital circuit having a dedicated power supply wiring for the substrate contact. An analog / digital mixed LSI characterized in that the dedicated power supply wiring and the circuit board dedicated power supply wiring for the analog circuit are shared and connected to the chip terminals.