JPS6282807A - Integrated circuit - Google Patents

Abstract

PURPOSE:To reduce reflection to be generated due to the shift of a terminal resistance value by arranging the terminal resistor in an integrated circuit package, connecting an external resistor to the outside of the package and setting up the parallel resistance value of both the resistors to a value approximate to characteristic impedance. CONSTITUTION:The resistor 3b on a chip 6a in the package 5 is a terminal resistor with a resistance value R2. Input impedance estimatng the chip 6a including the external resistor 3a arranged on a position separated from the package 5 by a distance A is regarded as the parallel connection value of resistance values R1, R2. Although the resistance value of the resistor 3b built in the chip 6a has about 20-30wt% variation, the external resistor 3a can be produced with the low variation of the resistance value. Thereby, the whole variation of resistance values can be suppressed at an extremely low value as compared with the variation of the resistance values of the resistor 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an integrated circuit for high-speed operation in which an input circuit is constituted by a transmission line having a predetermined characteristic impedance. especially,
This paper relates to the implementation of the terminating resistor of the transmission line.

〔overview〕

In an integrated circuit where the input circuit consists of a transmission line with a predetermined characteristic impedance and the reflection of the input circuit is reduced, a terminating resistor for this transmission line is provided inside the integrated circuit package, and an external terminal is provided for this transmission line outside the puff cage. By connecting additional resistors and creating a configuration in which the parallel resistance value of the two resistors approximates their characteristic impedance, reflections caused by differences in the values of the terminating resistors are reduced.

[Conventional technology]

Conventionally, as shown in FIG. 2, the output of an integrated circuit 1 is connected to one end of a transmission line 2, and the other end of the transmission line 2 is connected to a terminating resistor 3 that matches the transmission line characteristic impedance and a next-stage integrated circuit 4. Methods of transmitting are used in relatively high speed digital signal processing circuits.

Fig. 3 is an enlarged representation of the terminal resistor and subsequent parts, where 3 is the terminating resistor, 5 is the package, 6 is the integrated circuit chip, 7 is the transistor in the chip, and A is the length of the package lead. B is the wiring length inside the package case. As we will see, even if the terminating resistor 3 matches the transmission path characteristic impedance, the distance (A+B) from the position of the terminating resistor 3 to the transistor 7 in the chip 6 to which the signal is actually applied is the distance of the signal propagating there. There are cases where the rise, fall, and speed cannot be ignored. At this time, the signal applied to the transistor 7 is affected by reflection, causing waveform distortion. Furthermore, even if the lead wire portions 8 of A and B in FIG. The transmission line in the state is connected, and waveform distortion occurs in this case as well.

As a solution to this problem, as shown in FIG. 3' is built into the chip 6.

[Problem that the invention seeks to solve]

However, the terminating resistor 3' formed by the integrated circuit chip 6 in FIG. 4 is extremely small and has an accuracy of ±20
It is unavoidable that there will be an error of about ±30%. Therefore, both the cases of FIG. 3 and FIG. 4 have the disadvantage that mismatch with the transmission line causes reflection and waveform deterioration. Although it is possible to select the integrated circuit itself in order to suppress the variation in the built-in resistance to ±10% so as to suppress the deterioration caused by this reflection, in this case, the yield will deteriorate.

The present invention solves the above-mentioned problems, and aims to provide a waveform integrated circuit within a terminating resistor in which reflection deterioration is extremely reduced even if the integrated circuit has variations in characteristics.

Means for Solving Problem C] The present invention provides an input circuit that takes in an external signal, which is formed in a transmission line with a predetermined characteristic impedance, is built in a pancase, and has a connection point between the transmission line and an active element in the circuit. In an integrated circuit equipped with a terminating resistor having one end connected to a common potential point and the other end connected to a common potential point, an external resistor is connected between the transmission path outside the package and the common potential point. A parallel resistance value between the resistor and the terminating resistor is set to a value that approximates the characteristic impedance.

[For production]

Resistors built into the package are difficult to adjust and have large variations in value, but external resistors can be adjusted or selected. Most of the reflection that occurs on this transmission path can be absorbed by built-in resistors. Furthermore, by connecting an external resistor, some resistors will be connected in the middle of the transmission line, but by approximating the parallel resistance value of the two resistors to the characteristic impedance, it is possible to It can be seen that the input circuit of this integrated circuit closely approximates the value of the characteristic impedance, and the reflection in the transmission path of the input circuit can be substantially reduced.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings.

In Fig. 1, the output stage of the driving integrated circuit 1 is connected to the input of a transmission line 2 with a characteristic impedance R, and an external resistor 3a is connected to a portion A at a distance from the package with a resistance value R. be done.

The following length B is the wiring length within the package 5.

The portions indicated by A and B above are also on the extension of the transmission line 2 having the characteristic impedance R. The tip of the portion B is connected to an on-chip resistor 3b which connects the on-chip transistor to a common potential point with the transistor 7 on the integrated circuit chip 6a.

This in-chip resistor 3b is a terminating resistor with a resistance value R2 formed within the integrated circuit chip. In the case of FIG. 1, the input impedance considering the integrated circuit chip 6a including the resistor 3a external to the package can be considered to be approximately the parallel connection of resistance values R1 and R2. Here, the resistance value of the on-chip resistor 3b built into the integrated circuit chip 6a is ±20 to ±30 as described above.
However, since the externally attached resistor 3a can be manufactured with a small variation in resistance value, the overall resistance value variation can be suppressed to be much lower than that of the resistor 3b.

- For example, when obtaining a characteristic impedance of 50Ω, the resistance value may change by 130% in the conventional 50Ω internal circuit type, but if it is designed with R+ = 10QΩ and Rz = 100Ω, the resistance value R2 Even if R becomes +30%, that is, 130Ω, if the precision of the resistance value R is increased, the overall minimum value can be 56.5Ω, and the change from 50Ω is only 13%. Furthermore, the external resistor 3a
If the design allows the value of to be adjusted, the parallel resistance value of the two resistors can be made close to 50Ω.

〔Effect of the invention〕

As explained above, according to the present invention, most of the reflection is absorbed by the resistor connected to the end of the transmission line inside the puff cage, and furthermore, the impedance when looking at the input circuit of this integrated circuit from outside the integrated circuit is , the built-in resistor, the external resistor, and the combined resistor have a parallel resistance value, which can be a value that approximates the characteristic impedance of the transmission line.

Therefore, reflection can be reduced as a whole.

Therefore, even if the integrated circuit has large variations, it can be put to practical use, improving the manufacturing yield, and the adjustment accuracy of the characteristic impedance of the input circuit transmission path itself can be set more gently than before. This aspect also has the effect of reducing the number of manufacturing steps.

[Brief explanation of drawings]

FIG. 1 is a terminal resistor division mounting circuit diagram of an embodiment of the present invention. FIG. 2 is a circuit configuration diagram of a conventional example. FIG. 3 is a circuit diagram of another conventional example. FIG. 4 is a circuit diagram of a conventional integrated circuit with a built-in termination resistor. 1... Integrated circuit (drive side), 2... Transmission line (characteristic impedance R), 3.3'... H-end resistance, 3a...
・Package external resistor (resistance value Rr), 3b・
...Resistance inside the chip (resistance value R,), 4...Integrated circuit (
(Package 5.6.6a...Integrated circuit chip, 7...Transistor in chip, 8...
Transmission lead wire section, A, A'... Pan cage lead section, B, B'... Wiring inside the package.

Claims (1)

[Claims] (1) An input circuit that takes in an external signal is formed on a transmission path with a predetermined characteristic impedance, is built into a package, and one end is connected to the connection point between the transmission path and the active element in the circuit, and the other end is connected to a common potential point. In an integrated circuit equipped with a terminating resistor connected to an external resistor, an external resistor is connected between the transmission line outside the package and a common potential point, and the parallel resistance value of this external resistor and the terminating resistor is An integrated circuit characterized in that the characteristic impedance is set to a value approximating the characteristic impedance described above.