JP2003332442A - Noise detecting method and substrate produced based thereon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a method which enables the correct application of feedback on designing by detecting minute substrate noise among crosstalk noise, power supply noise and the substrate noise and a substrate produced based on the detecting method. <P>SOLUTION: On an LSI chip 401 being an object to be measured is provided a noise source 402 such as a digital circuit and a digital circuit and an analog circuit 403 which is feared to be affected by the noise source 402, and a ring oscillator (ROSC) measuring circuits 404 for measuring substrate noise is arranged in the periphery of the digital circuit and analog circuit 403. The measuring circuit 404 is constituted of a ring oscillator constituted of an odd number of inverters, PMOS transistors of open drain and an inverter for converting and amplifying the output of the ring oscillators to output the same into the PMOS transistors. The jitter amounts of phase noise of the ring oscillators are detected to specify the frequency of noise generated from the noise source. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate noise detecting method, and more particularly to a substrate noise detecting method characterized in that a minute signal of the substrate noise is measured by using an output of an oscillation circuit which is easily influenced by the substrate noise. Regarding

[0002]

2. Description of the Related Art In recent years, the operating frequency of computers has become higher, and along with this, the noise generated by LSIs has tended to increase. Noise generated by the LSI includes crosstalk noise, power supply noise, substrate noise, and the like.

Even if the signal wirings are physically separated from each other, the crosstalk noise is capacitively connected. Therefore, the noise generated when the signal in one signal wiring changes, This is noise that is transmitted to the signal wiring.

Power supply noise is noise superimposed on the power supply supplied to the power supply line inside the LSI from the power supply pins of the printed circuit board or the LSI package.

Substrate noise is noise transmitted through a semiconductor substrate in an LSI chip.

Various measures have been taken so far with respect to crosstalk noise and power supply noise, but with respect to substrate noise propagating through a semiconductor substrate, sufficient measures have not yet been established. . In particular, in an LSI chip in which a digital circuit and an analog circuit are mixedly mounted, it has been found that noise generated in the digital circuit adversely affects the analog circuit through the substrate even if the power supplies for the digital circuit and the analog circuit are separated. There is.

FIG. 10 is a cross-sectional view showing a propagation state of noise as described above. Substrate noise 904 generated in the digital circuit unit 902 formed on the n-type substrate 901 propagates through the inside of the substrate to the analog circuit unit 903 formed on the same surface as the digital circuit 902.

In order to design a chip in which the above-mentioned substrate noise is suppressed, it is necessary to grasp the amount of substrate noise. However, since this substrate noise is a minute signal and also propagates through the silicon substrate in the chip, it is very difficult to detect.

[0009]

Among the crosstalk noise, the power supply noise, and the substrate noise generated by the LSI, sufficient measures have not been established for the substrate noise. In order to design a chip in which substrate noise is suppressed, it is necessary to grasp the amount of substrate noise, but it is very difficult to detect substrate noise.

The present invention has been made in view of the problems of the above-described conventional technique, and is to realize a method for detecting a minute substrate noise and accurately providing feedback to the design, and a substrate by the method. With the goal.

[0011]

According to the noise detecting method of the present invention, an oscillating circuit is arranged in the vicinity of the noise source, and the frequency of the noise generated by the noise source is specified by observing the output of the oscillating circuit. Characteristically, the substrate has a noise source and an oscillation circuit arranged in the vicinity of the noise source.

In this case, the oscillator circuit may be composed of a ring oscillator.

The oscillator circuit may be surrounded by a guard ring.

Further, the output section of the oscillation circuit may be constituted by an open drain type transistor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the structure of the essential part of an embodiment according to the present invention, and FIG. 2 is a top view showing its mounting state.

The substrate noise detection according to the present invention is, as shown in FIG. 1, a ring oscillator 104 composed of an odd number of inverters 101 connected in series and whose output is fed back to an input, and an open drain PMOS transistor. 103 and an inverter 102 that inverts and amplifies the output of the ring oscillator 104 and outputs it to the PMOS transistor 103.

The ring oscillator 104 is, for example, a CMOS having a gate length L = 0.16 μm and a gate width W = 2 μm.
Using the inverter 101 connected in 29 stages,
As the S transistor 103, L = 0.16 μm, W =
The one with 80 μm is used. The inverter 102 inserted between the PMOS transistor 103 and the ring oscillator 104 is provided for waveform shaping. As a specification of the inverter 102, for example, L = 0.1
6 μm and W = 2 μm.

The PMOS transistor 103 is surrounded by, for example, a triple guard ring 201 so as not to be influenced by substrate noise at the output stage, and the ring oscillator 104 is provided.
In order to separate from the influence of the power supply noise of, the power supply of only the PMOS transistor 103 is prepared. Then, the output of the ring oscillator 104 is output to the output pad 202 through the PMOS transistor 103, and its waveform is observed.

FIG. 3 is a diagram showing the configuration of a measurement system for observing a waveform.

The output of the DUT 301 is divided by the branch circuit 302. One output of the branch circuit 302 is supplied to the trigger input of the oscilloscope 304, and the other output is supplied to the signal input of the oscilloscope 304 via the delay line 303. The delay line 304 is provided to correct the delay amount in the signal conversion module provided in the oscilloscope 304.

FIG. 4 is a perspective view showing a concrete structure of the DUT 301.

The LSI chip 401 is provided with a noise source 402 such as a digital circuit and a digital circuit / analog circuit 403 in which influence from the noise source 402 is concerned. Substrate noise is generated around the digital circuit / analog circuit 403. A ring oscillator (ROSC) measurement circuit 404 having the configuration shown in FIGS. 1 and 2 is provided for observation.

Waveforms observed in this embodiment having the above-described measurement configuration will be described. FIG. 5 is a diagram for explaining the amount of jitter when there is no influence of substrate noise, and shows an actual noise waveform, the total amount of the noise waveform, and a graph in order from the top of the drawing.

When there is no influence of the substrate noise, the amount of phase noise jitter of the ring oscillator increases as time elapses from the trigger point, as shown in FIG. This tendency of increase is observed as an influence of thermal noise of the transistor near the trigger point and as an influence of 1 / f noise as the distance from the trigger point increases. The increasing function of the amount of jitter due to the phase noise of these ring oscillators and the increasing function of the jitter due to the thermal noise of the transistor are different, and are shown in FIG. 6, for example. When substrate noise is added in this state, as shown in FIG. 7, the influence of the noise on the transistor thermal noise region appears significantly and the jitter becomes large. Then, at the 1 / f noise area where the influence of noise is small, the behavior is such that the amount of jitter becomes small.

In FIGS. 5 and 6, the measurement is performed from 20 ns to 150 ns. This measurement range may be appropriately changed according to the noise frequency. For example, when measuring high frequency noise, it may be sufficient to measure up to 40 ns.

FIG. 8 is a diagram for explaining the above phenomenon. As shown in FIG. 8, when the distance from the noise source is increased,
It can be seen that the normal time dependence of jitter returns.
Further, this movement largely depends on the frequency of the substrate noise, and the test LSI can detect the effect of the frequency having a great influence on the circuit. In an actual chip (or test LSI), the influence of the substrate noise can be estimated by installing the detection circuit according to the present embodiment near a circuit whose noise condition is to be measured, such as a circuit to be measured. .

In this embodiment, the jitter characteristic of the ring oscillator 102 is used. Ring oscillator 102
Jitter increases with time according to a theoretically measurable increase tendency, but it periodically fluctuates when substrate noise is added. Therefore, the added substrate noise can be observed by observing the periodic fluctuation of the jitter.

From the observed jitter waveform, the dominant noise frequency can be obtained by measuring the period as shown in FIG.

In general, it is difficult to directly detect noise. This is because even if a circuit for detecting noise is manufactured, the noise detection circuit itself may be affected by noise. In this embodiment, the ring oscillator 102 is used as a damage circuit, in which the influence of noise significantly affects the output, and the substrate noise that is difficult to detect is detected by an indirect method of observing the jitter output waveform. .

In this embodiment, the ring oscillator 102 is used as the damage circuit, but this is used because the output frequency and the oscillation frequency can be easily created. The present invention is not limited to this. The invention can be applied to the present invention as long as an oscillation output is possible, and various configurations such as a circuit using a crystal oscillator, an RLC circuit, and a circuit using an operational amplifier can be employed.

Regarding the oscillating frequency of the oscillating circuit which is the damage circuit, it may be higher than the expected frequency of the noise source. If the frequency of the noise source is unpredictable, the frequency should be set as high as possible. At this time, if the oscillation frequency becomes too high, the LSI
It will be difficult to pull the signal off the chip. In such a case, a circuit for measuring jitter may be included in the LSI chip.

Further, although the PMOS transistor 103 is of open drain type, this is for the purpose of shaping the waveform before outputting to the detection portion so as to make it resistant to noise. For this reason, the detection part may be protected against noise by using other means such as protection by a guard ring. In such a configuration, it is not necessary to adopt the open drain type and other circuit forms May be

An application example of this embodiment is LSI.
One example is to configure a jitter detection circuit in the chip and output the jitter during operation by an external command as data every machine cycle.

Further, in order to detect noise at different points in the LSI chip, a jitter detecting circuit capable of individually operating by different operation input pins may be formed at different points. With such a configuration, the LSI
Substrate noise can be detected at various points within the chip.

In the present invention, the dominant frequency of substrate noise can be obtained as described above. Therefore, the PLL
By setting the effective frequency of the filter provided in the analog circuit portion such as the circuit as the dominant frequency of the detected substrate noise, a more effective circuit can be efficiently designed.

Further, by detecting how much the delay of the inverter forming the clock circuit is delayed by noise, the accuracy of verifying the logic timing of the LSI chip can be improved.

[0038]

According to the present invention, it is possible to accurately estimate the influence of a substrate noise, which is a minute signal, on a circuit on an actual chip, and a design for noise propagated through a silicon substrate, which has been difficult in the past, can be performed. As possible,
It can also contribute effectively to the creation of rules for circuit layout.

[Brief description of drawings]

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

FIG. 2 is a top view showing a mounting state of the embodiment shown in FIG.

FIG. 3 is a diagram showing a configuration of a measurement system for observing a waveform.

4 is a perspective view showing a specific configuration of the DUT 301 shown in FIG.

FIG. 5 is a diagram for explaining a jitter amount when there is no influence of substrate noise.

FIG. 6 is a diagram showing an increasing function of jitter amount due to phase noise of a ring oscillator and an increasing function of jitter amount due to thermal noise of a transistor.

7 is a diagram showing a state in which substrate noise is added to the increasing function shown in FIG.

FIG. 8 is a diagram for explaining a movement in which the amount of jitter becomes small in a region of 1 / f noise where the influence of noise is small.

FIG. 9 is a diagram for explaining a state of obtaining a dominant noise frequency from an observed jitter waveform.

FIG. 10 is a cross-sectional view showing a propagation state of noise.

[Explanation of symbols]

101 inverter 102 inverter 103 PMOS transistor 104 ring oscillator 201 guard ring 202 output pad 301 DUT 302 branch circuit 303 delay line 304 oscilloscope 401 LSI chip 402 noise source 403 Digital circuit / Analog circuit 404 ROSC measurement circuit

Claims (8)

[Claims] 1. A noise detecting method, wherein an oscillating circuit is arranged in the vicinity of a noise source, and the frequency of noise generated by the noise source is specified by observing the output of the oscillating circuit. 2. The noise detecting method according to claim 1, wherein the oscillation circuit is composed of a ring oscillator. 3. The noise detecting method according to claim 1 or 2, wherein the oscillation circuit is surrounded by a guard ring. 4. The noise detecting method according to claim 1, wherein the output portion of the oscillation circuit is formed by an open drain type transistor. 5. A substrate having a noise source and an oscillation circuit arranged near the noise source. 6. The substrate according to claim 5, wherein the oscillation circuit is composed of a ring oscillator. 7. The substrate according to claim 5, wherein the oscillation circuit is surrounded by a guard ring. 8. The substrate according to claim 5, wherein the output portion of the oscillation circuit is composed of an open drain type transistor.