JPH02126718A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To prevent the influence of noise generation due to spurious radiation from inflicting on another circuit set together with a microcomputer by providing a means to multiply the frequency of an oscillator in the internal part. CONSTITUTION:A microcomputer is provided on the same semiconductor substrate and a multiplier 4 to multiply the frequency of a basic clock supplied to the microcomputer is provided. The clock pulse inputted to the multiplier 4 is taken out from the multiplier 4 as a clock pulse having a double frequency and used as the basic clock of the microcomputer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor integrated circuit having an oscillator that generates a basic clock and a microcomputer on the same semiconductor substrate.

[Conventional technology]

Conventionally, in order to increase the operating speed of a microcomputer, it was necessary to increase the frequency of the basic clock, which led to increasing the frequency of an oscillator external to the integrated circuit.

[Problem to be solved by the invention]

In the conventional semiconductor integrated circuit described above, when increasing the operating speed of the microcomputer, the frequency of the oscillator external to the integrated circuit was increased, so that spurious radiation emitted from the oscillation terminal of the integrated circuit was transmitted to other circuits set at the same time. In particular, it has the disadvantage of generating noise in high frequency circuits (televisions, VTRs, radios, etc.) that have recently come to be used with microcomputers.

[Means to solve the problem]

The semiconductor integrated circuit of the present invention has internal means for multiplying the frequency of the oscillator.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 1 is a semiconductor integrated circuit, 2 and 3 are oscillation terminals, 4 is a multiplier, 5 is a crystal oscillator, 6 and 7 are capacitors for adjusting the oscillation frequency, 8 has a phase of 18
The amplifier inverts 0 degrees, 9 is a self-biasing resistor. As shown in detail in FIG. 2, the multiplier 4 includes delay elements 10. NAND gate 11. Inverter game) 12,1
4. It consists of NOR gates 13 and 15.

FIG. 3 shows the input waveform 16 to the multiplier 4. Delay element 10
Output waveform 17. Output waveform 18 of inverter gate 12
．． An output waveform 19 of the NOR gate 15 and an output waveform 20 of the inverter gate 14 are shown.

As can be seen from the above, the clock pulse input to the multiplier 2 is extracted from the multiplier as a clock pulse having twice the frequency and used as the basic clock of the microcomputer.

〔Effect of the invention〕

As explained above, the present invention increases the frequency of the basic clock by multiplying the frequency of the oscillator inside the integrated circuit without increasing the frequency of the oscillator outside the integrated circuit. In particular, it is effective in increasing the operating speed of a microcomputer without affecting high frequency circuits such as televisions, VTRs, radios, etc. by noise generation due to spurious radiation from the oscillation terminals of integrated circuits.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a logic diagram of the multiplier shown in FIG. 1, and FIG. 3 is a waveform diagram output from each gate in FIG. ■... Semiconductor integrated circuit, 2, 3... Oscillation terminal, 4... Multiplier, 5... Crystal oscillator, 6, 7... ...Capacitor for oscillation frequency adjustment, 8.
...Amplifier whose phase is inverted by 180 degrees, 9...
... Self-bias resistance, lO ... Delay element, 11 ... NAND gate, 12゜14 ...
...inverter game), 13.15...NO
R gate, 16...Input waveform to multiplier 4, 1
7... Output waveform of delay element 10, 18...
...Output waveform of inverter gate 12, 19...
...N. Output waveform of R gate 15, 20... Output waveform of inverter gate 14. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A semiconductor integrated circuit comprising a microcomputer on the same semiconductor substrate and further comprising means for multiplying the frequency of a basic clock applied to the microcomputer.