JPS6254457A - Input/output circuit for integrated circuit - Google Patents

Abstract

PURPOSE:To realize a multi-functional high integration by a method wherein AC signals inputted at an IC first pin is supplied to a signal-processing circuit through a buffer circuit capable of transmitting only AC signals and, simultaneously, DC signals are caused to be inputted into or outputted from a DC signal circuit in the IC at said IC first pin. CONSTITUTION:DC signals 26 are outputted at a pin 23 and, simultaneously, AC signals 21 may be supplied to a chroma signal processing circuit 25 through the pin 23 and buffer circuit 24 because changes in the DC potential at the pin 23 are stopped by the buffer circuit 24. That is to say, the buffer circuit 24 provided between the pin 23 and chroma signal processing circuit 25 enables a single pin to serve multiple purposes. In a circuit designed as such, the inputting of AC signals, inputting of DC signals, and outputting of DC signals may be accomplished by using a single pin. The number of pins required in an IC may be decreased and a circuit, capable of a multiplicity of functions and enhanced in integration, may be built in a single chip.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an input/output circuit for an integrated circuit that makes it possible to reduce the number of input/output bins for AC signals and DC signals.

[Technical background of the invention]

2. Description of the Related Art In recent years, ICs (integrated circuits) used in electronic devices are becoming increasingly integrated with multiple functions, in which more circuit functions are configured on one chip. the current.

Among the ICs used in TV receivers, so-called 1-chip ICs have also appeared, and the number of ICs used has reached 64.

FIG. 3 shows an example of a typical input/output circuit used in a conventional video chroma circuit IC for a television receiver. The AC signal 1 is applied to the input bin 3 of the IC 20 via the content CI, and is supplied from this pin 3 to the chroma signal processing circuit 4 in the IC. The chroma signal processing circuit 4 is composed of a double balanced adjustment circuit using transistors Ql to Q6. On the other hand, the IC2 is provided with a DC signal output pin 5 and a DC signal input pin 6.
The field frequency (50I(z
A judgment signal (DC signal) 8 of 60 Hz) is obtained, which is led to the output pin 5 through an amplifier 9 using a transistor Q7, and further outputted to an external circuit as a field frequency switching signal via an amplifier 10 outside the IC. Ru. For input pin 6, mute signal (DC signal) 11
are applied to input pin 6 through amplifier 12, and from this pin 6 transistors Q8. Differential amplifier 1 using Q9
3 and an amplifier 14 using a transistor Qlo, the signal is supplied to a mute circuit 15. The mute circuit 15 is a circuit configured to attenuate the video signal all at once using externally inputted mute FF4.

[Second point in technology] By the way, in ICs, especially analog ICs, there is a limit to how much the number of pins can be increased due to the relationship with the package. Therefore,
In order to achieve more multi-functionality and higher integration, technology for effective use of bins is required.

However, in the above-mentioned conventional IC, the input bin 3 for AC signals and the input pin 6 or output bin 5 for DC signals are required in No. 1 due to the circuit configuration, so it is difficult to minimize the number of bins. The drawback was that it was impossible due to the circuit.

[Purpose of the invention]

An object of the present invention is to provide an input/output circuit for an integrated circuit that is capable of inputting an AC signal and inputting or outputting a DC signal using one pin, and is suitable for multifunctional and highly integrated circuits.

[Summary of the invention]

The circuit of the present invention is an IC in which functional circuits for AC signals and DC signals are configured inside the IC, and AC signals and DC signals are input or output via pins. Signal.

The AC signal is configured to be supplied to the signal processing circuit through a buffer circuit that transmits only the AC signal, and at the same time, the DC signal is input to or output from the first pin to the DC signal circuit inside the IC.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing one embodiment of an input/output circuit of an integrated circuit according to the present invention. This embodiment consists of an AC signal input circuit (chroma signal input circuit) and a DC signal output circuit (50
/60Hz discrimination signal output circuit).
An example of a circuit realized using two bins is shown.

In this figure, an AC signal 21 is applied to a pin 23 of an IC 22 via a capacitor C1l, and is passed through a buffer circuit 24 to a chroma signal processing circuit 25.
supplied to The buffer 1 circuit 24 is a transistor Qll.
and its emitter ground Il
The AC signal 21 is input from the pin 23 to the base of the transistor Q1t, and is supplied from the emitter of the transistor Qll to the next stage chroma signal processing circuit 25 through the capacitor C12. In this case, the buffer 1 circuit 24
The chroma signal processing circuit 2 cuts off the DC component and only outputs the AC signal.
5. The chroma signal processing circuit 25 is composed of a double balanced demodulation circuit using transistors Q12 to Qzy and a constant current source 112. On the other hand, the DC signal 26 is output from the 50760Hz discrimination circuit 27 in the IC, and is sent to the amplifier 28.
The signal is output to pin 23 via pin 23, and is transmitted from pin 23 to an external circuit of the IC through an interface circuit 29 external to the IC. 50/60) The iz discrimination circuit 27 is a PAL television system.

When configuring a video chroma circuit IC that supports all systems such as NTSC and SECAM! A circuit is required to determine whether it is PAL reception, NTSC reception, or SECAM reception, and it detects the field frequency (50Hz or 60'Hz) and if it is 50) Iz, then S
It determines whether ECAM reception is being received, and outputs a DC level signal to switch various circuits to suit each television system according to the determination result. That is, 5076
The 0Hz discrimination circuit 27 is a circuit that outputs different DC levels at 50Hz and 60Hz. The amplifier 28 is constituted by a grounded emitter circuit using a transistor Q18. The external interface circuit 29 is constructed using a transistor Q19 with a resistor divider circuit and a capacitor arranged at its base, and is a circuit for obtaining a voltage level suitable for the external circuit.

In the circuit configured as above, the DC signal 26 is
Even if the DC potential of the bin 23 changes at the same time as the AC signal 21 is output through the bin 23.3, the buffer circuit 24 blocks the change in the DC potential. Similar to the conventional AC signal input circuit (chroma signal input circuit) shown in FIG.
can be supplied to That is, by providing the back 7 circuit 24 between the bin 23 and the chroma signal processing circuit 25, the same function can be realized with one bin, whereas conventionally two input/output pins were required.

Figure 2 is a circuit diagram showing another embodiment of the present invention. This example shows a circuit example in which two input/output circuits, the AC signal input circuit (chroma signal input circuit) and the DC signal input circuit (mute signal input circuit) shown in Fig. 3, are realized by using one pin. .

In this figure, an alternating current signal 31 is applied to a bin 33 of an IC 32 via a capacitor Cn, and is supplied through this bin 33 to a chroma signal processing circuit 35 via a buffer circuit 34. Buffer 1 circuit 34 is transistor Q21
, consisting of a constant 4-current source I21 and a capacitor C21,
The chroma signal processing circuit 35 includes transistors Q22 to Q27.
It consists of a double balanced demodulation circuit using a constant current g I22. The DC signal 36 is applied to the bin 33 via an amplifier 37 using a transistor Q28, and from the bin 33 it is applied to a differential amplifier 38 using transistors Q29 and Qao.
and is supplied to a mute circuit 40 via an amplifier 39 using a transistor Q31. The mute circuit 40 is a circuit for video conferencing.

In the embodiment shown in FIG. 2, just like the embodiment shown in FIG. Signal 36 can be input to each functional circuit within IC 32.

In each of the embodiments shown in FIGS. 1 and 2, the AC signal circuit inside the IC is a chroma signal processing circuit, and the DC signal circuit is a
Although the case where the circuit is a 60Hz discrimination circuit or a mute circuit is described, the present invention is not limited to the circuits shown in these embodiments, but generally applies to AC signal circuits and DC signal circuits configured for each function in an IC. It can be applied to an integrated circuit that allows an AC signal to be input into a signal circuit, while a DC signal can be input to or output from a pin.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to input an AC signal and input or output a DC signal using one bin, and the number of pins of an IC can be reduced.

Therefore, for example, it is possible to configure a highly integrated circuit with multiple devices in one chip (one chip at a time).

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of an input/output circuit of an integrated circuit according to the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the present invention.
□, FIG. 3 is a circuit diagram showing an input/output circuit of a conventional integrated circuit. 21.31...AC signal, 22.32...IC. 23. 33...bin, 24.34...
buffer circuit. 25.35...Chroma signal processing circuit. 26.36...DC signal. 27-50760 Hz discrimination circuit-40...Mute circuit.

Claims (1)

[Scope of Claims] An integrated circuit configured with an AC signal processing circuit that inputs an AC signal and processes the signal, and a DC signal circuit that inputs or outputs a DC signal; and one pin for inputting the DC signal to the DC signal circuit or outputting it from the DC signal circuit, and a DC signal provided between this pin and the AC signal processing circuit, and a DC signal input to the pin. An input/output circuit for an integrated circuit, comprising a buffer circuit for blocking alternating current components and transmitting only alternating current components to the alternating current signal processing circuit.