JPH0783091B2 - Semiconductor integrated circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit provided with an amplifier or the like whose operation can be selectively switched, and more particularly to suppression of a parasitic transistor at the time of operation switching.

[Conventional technology]

In general, tape recorders and video tape recorders have signal systems for recording and playback, and these signal systems are selectively switched to set the recording mode and playback mode. In the selecting system, a signal switch circuit for selecting and extracting a plurality of input signals is installed. And this kind of signal switch circuit is designed to reduce the size and increase the reliability of signal switching.
Composed of.

FIG. 2 shows an equivalent circuit of the signal switch circuit made into an IC. In this signal switch circuit, two amplifiers 2A and 2B are installed in order to selectively switch the signals of two channels, and the input terminals 4A and 4B individually input sine wave signals or pulses from each system. The signal Si is added. A common output stage amplifier 6 is installed for each amplifier 2A, 2B.

The amplifiers 2A and 2B are provided with transistors 14 and 16 forming a current mirror circuit as a common active load for the differential amplifier 12 formed of the transistors 8 and 10, and the transistors on the base side of the input side transistor 8 are transistors. A pre-stage amplifier that also functions as a bias circuit for the transistor 8 composed of 18 and the resistor 20 is installed. The constant current from the constant current source 22 is generated by the transistors 24, 26, 28, 30 and the resistors 32, 34, 36, 38 forming the current mirror circuit, and the transistors 8, 10 forming the differential amplifier 12 and the preceding stage. It is supplied to the emitter side of the transistor 18 as an amplifier, but a switch circuit 40 is installed for the constant current source 22 of each amplifier 2A, 2B, and the constant current supply is selected and selected according to the switching. The operation of the amplifiers 2A and 2B is switched according to the input signal to be output.

The output signal of the amplifier 2A or the amplifier 2B obtained by selecting the operation of the amplifiers 2A and 2B is added to the output stage amplifier 6. The output stage amplifier 6 includes transistors 46 and 48 and diodes 50 and 52 that form a bias circuit for the output transistors 42 and 44, and the transistor 46 and
And a transistor 54 forming a current mirror circuit are installed, and a constant current from a constant current source 56 is passed through the transistor 54 to a transistor 46, diodes 50 and 52, and a transistor.
The signal is supplied to the 48 side, and the output signals of the amplifiers 2A and 2B are added to the transistor 48.

Therefore, in such a signal switching circuit, the switching circuit 40 is switched for the signal applied to the input terminals 4A and 4B, and _{one of} the constant currents I ₁ and I _{2 is} supplied to the amplifier 2
By selecting the operation of A or 2B, the input signal can be passed and added to the output stage amplifier 6 and taken out from the output terminal 58. The amplifiers 2A and 2B have a common feedback terminal.
60 is provided, and the output of the output stage amplifier 6 is fed back to the feedback terminal 60 via a feedback element.

[Problems to be solved by the invention]

By the way, in this signal switch circuit, even when any of the amplifiers 2A and 2B is switched to the cut-off state,
As shown in FIG. 3, a leak current Ir flows through the transistor 18, and such a leak current Ir is remarkable at high temperatures.

Due to such a leak current Ir, a very low level bias current i is applied to the transistor 18.

When such a bias current i is applied, as shown in FIG. 4, the bias current i is also applied to the parasitic transistor 62 adjacent to the transistor 8 at a very low level. At this time, if the base-emitter voltages of the transistors 48 and 18 are V _F1 , V _F2 and the base-emitter voltage of the parasitic transistor 62 is V _FS , the relationship of V _F1 ≈ V _F2 + V _FS (1) To establish. As a result, a current flows from the collector to the emitter side of the transistor 8, and the original collector is changed to the emitter, and the reverse β state is reached, and the signal from the amplifier 2A or the amplifier 2B side in the cut-off state passes through the parasitic transistor 62. It is propagated to the amplifier 2B or the amplifier 2A on the channel side which is in a reverse phase and is in conduction.

FIG. 5 shows the state in which the parasitic transistor 62 occurs with respect to the transistors 8 and 10.

In the case of this semiconductor integrated circuit, after the buried layer 66 formed of the N-type high-concentration region is formed on the semiconductor substrate 64 formed of the P-type semiconductor, the N-type epitaxial layer 68 is formed, and the transistor 8 is formed on the epitaxial layer 68. , 10 are partitioned and separated from other parts by the installation of a separation region 70 composed of a high-concentration P-type diffusion region.

Then, in the inner surface layer of the epitaxial layer 68 surrounded by the classification region 70, an N-type high-concentration region is selectively formed and the base 72 is installed, and a plurality of P-type high-concentration regions are formed. To form collectors 74, 76 and emitter 78,
The transistors 8 and 10 are formed. Note that V _F1 and V _F2 represent bias voltage sources.

Therefore, the parasitic transistor 62 is generated by using the base 72 of the transistor 8 as the base, the collector 76 as the emitter, and the P-type isolation region 70 as the collector, and the bias current i is given to the transistor 18 by the leak current Ir.
The parasitic transistor 62 is also biased and operates, causing an unnecessary signal to have an opposite phase and leak to the other channel side.

Therefore, an object of the present invention is to provide a semiconductor integrated circuit in which the operation of such a parasitic transistor is suppressed to prevent signal leakage.

[Means for solving problems]

The semiconductor integrated circuit of the present invention has a plurality of amplifiers 2A and 2B whose operations are selectively switched, as illustrated in FIG.
Is installed, and a PNP transistor 18 is provided at each signal input portion of the input signal to be amplified by each amplifier.
Of the PNP transistor 1 when the input signal is applied to the amplifiers 2A, 2B through the base-emitter of the transistor 18 to selectively stop the operation of the amplifier.
A semiconductor integrated circuit in which a PNP-type parasitic transistor 62 having an emitter side of 8 as a base, a collector side of the transistor 8 installed in the amplifiers 2A and 2B as an emitter, and a substrate side of the transistor 8 as a collector, is generated by the PNP-type transistor. When the collector side of 18 is grounded and a current supply means (constant current source 80) is connected to the emitter side thereof to stop the operation of the amplifier, the current supply means is provided to the emitter side of the PNP transistor 18. A current is supplied from the (constant current source 80) and the emitter potential thereof is maintained at a level at which the parasitic transistor 62 is not activated.

[Action]

The semiconductor integrated circuit of the present invention supplies current from the current supply means (constant current source 80) to the PNP type transistor 18 installed in the signal input section of the amplifiers 2A and 2B regardless of the operating states of the amplifiers 2A and 2B. That PNP transistor 1
8 is put into an operating state, the emitter potential thereof is maintained at a level at which the parasitic transistor 62 is not activated, and the operation of the parasitic transistor 62 is suppressed.

Therefore, the amplifier 2A or the amplifier that has stopped operating
From the 2B side to the operating amplifier 2B or amplifier 2A side,
It is possible to prevent signal leakage due to the occurrence of the parasitic transistor 62.

〔Example〕

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

FIG. 1 shows an embodiment of a semiconductor integrated circuit of the present invention.

As shown in FIG. 1, this semiconductor integrated circuit constitutes a signal switch circuit similar to the signal switch circuit shown in FIG. That is, this signal switch circuit is provided with amplifiers 2A and 2B, and switches the operation of the amplifiers 2A and 2B in response to the input signal applied to the input terminals 4A and 4B.
The output signals obtained from 2A and 2B are taken out in addition to the output stage amplifier 6 commonly installed for each amplifier 2A and 2B.

Each of the amplifiers 2A and 2B is provided with transistors 14 and 16 forming a current mirror circuit as a common active load with respect to the differential amplifier 12 formed of the transistors 8 and 10, and the base side of the transistor 8 of the signal input section. A pre-stage amplifier that shares a bias circuit for the transistor 8 composed of the PNP type transistor 18 and the resistor 20 is installed in. The constant current from the constant current source 22 is supplied to the transistors 8 and 10 of the differential amplifier 12 by the transistors 24, 28 and 30 and the resistors 32, 36 and 38 which form the current mirror circuit.
A switch circuit 40 is installed for the constant current source 22 of each amplifier 2A, 2B, the supply of constant current is selected according to the switching, and the operation of the amplifier 2A, 2B is switched according to the input signal to be selected. To be

Then, a constant current source 80 as a current supply means is separately installed for the current supply system for supplying the operating currents to the transistors 8 and 10 which form the differential amplifier 12, and the constant current source 80
Is always supplied to the emitter of the transistor 18 installed on the base side of the transistor 8.

In this case, the constant current source 80 constitutes a circuit different from the constant current source 22, outputs a constant current regardless of the switching of the switch circuit 40, and is independent of the operating state of each amplifier 2A, 2B. Transistor 18 is biased.

Then, the output signal of the amplifier 2A or the amplifier 2B obtained by selecting the operation of the amplifiers 2A and 2B is added to the output stage amplifier 6. The output stage amplifier 6 includes output transistors 42 and 44.
In addition to installing the transistors 46 and 48 and the diodes 50 and 52 that configure the bias circuit, the transistor 46 that configures the current mirror circuit with the transistor 46 is installed, and the constant current from the constant current source 56 is passed through the transistor 54. Is supplied to the transistor 46, the diodes 50 and 52, and the transistor 48. The output signal of each amplifier 2A, 2B is
In addition to the transistor 48, the output of the output stage amplifier 6 is taken out from the output terminal 58. Also, each amplifier 2A,
A negative feedback signal NF is applied to the feedback terminal 60 provided at the base of the 2B transistor 10 from the output terminal 58 of the output stage amplifier 6 via a feedback circuit (not shown).

Therefore, in this semiconductor integrated circuit, the switch circuit 40
A bias current is supplied from the constant current source 80 to the transistor 18 regardless of the operating state of the differential amplifier 12 of the amplifiers 2A and 2B by switching the transistor 18, the transistor 18 is maintained in the conductive state, and its emitter potential is The PNP type parasitic transistor 62 is maintained at a level at which it is not activated.

In this case, the biases of the transistors 8 and 48 and the parasitic transistor 62 shown in FIG. 4 have a relationship of V _F1 << V _F2 + V _FS (2), and the parasitic transistor 62 is inactive. As a result, as shown in FIG.
It is possible to prevent signal leakage from the amplifier 2A or amplifier 2B in the off state to the amplifier 2B or amplifier 2A side in the operating state.

In the embodiment, the constant current source 80 is installed as the current supply means for the PNP type transistor 18 installed in the signal input section of the amplifiers 2A and 2B, but as the current supply means for the PNP type transistor 18, the PNP type transistor 18 is used. The constant current source 80 is not limited to the constant current source 80 as long as it is composed of an element such as a resistor having a current supply capability for maintaining the emitter potential of 18 at a level at which the parasitic transistor 62 does not occur.

〔The invention's effect〕

As described above, according to the present invention, the PNP installed in the signal input section of the amplifier is irrespective of the operating state of the amplifier.
The current is supplied from the current supply means to the P-type transistor to operate the PNP-type transistor and suppress the activation of the PNP-type transistor. On the other hand, it is possible to prevent signal leakage due to activation of the parasitic transistor.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an equivalent circuit of an embodiment of a semiconductor integrated circuit of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit of a semiconductor integrated circuit which constitutes a conventional signal switch circuit, and FIG. FIG. 4 is a circuit diagram showing an amplifier on the cut-off side of the semiconductor integrated circuit shown in FIG. 4, FIG. 4 is a circuit diagram showing occurrence of parasitic transistors in the amplifier shown in FIG. 3, and FIG.
It is sectional drawing which shows the structure of the semiconductor integrated circuit of a figure. 2A, 2B …… Amplifier 8 …… Transistor 18 …… PNP type transistor 62 …… Parasitic transistor 80 …… Constant current source (current supply means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 23/62 // G11B 5/027 502 B 7426-5D H03F 3/72 H03K 17/16 A 9184 -5J 17/62 Z 9184-5J

Claims (1)

[Claims] 1. A plurality of amplifiers whose operation is selectively switched are installed, and a PNP type transistor is provided at each signal input portion of an input signal to be amplified of each amplifier.
The input signal is applied to the amplifier through the base-emitter of the P-type transistor and the operation of the amplifier is selectively stopped, the emitter side of the PNP-type transistor is the base, and A semiconductor integrated circuit in which a PNP type parasitic transistor having a collector side as an emitter and a substrate side as a collector occurs, wherein the collector side of the PNP type transistor is grounded, and a current supply means is connected to the emitter side thereof. A semiconductor integrated device characterized in that, when the operation of the amplifier is stopped, a current is caused to flow from the current supply means to the emitter side of the PNP type transistor and the emitter potential thereof is maintained at a level at which the parasitic transistor is not activated. circuit.