JPH1013211A - Ecl circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ECL circuit which keeps its resistance to the power voltage by placing a transistor TR between a common emitter of a switching TR pair and a TR that functions as a constant-current source. SOLUTION: When the input voltage VIN is kept at a power supply GND that is higher than the reference voltage VR, the TRs Q1 and Q2 are turned on and off respectively, and a current flows to the TRs Q1, Q3 and Q4 and a resistance R12 from the GND. Then the collector potential of the TR Q2 rises up to the GND potential, and the output potential of an output terminal OUT lowers from the GND potential by a degree equal to the base-emitter forward voltage VF of a TR Q5 and is set at an H-level. While when the VIN is kept at the GND lower than VR, the TRs Q1 and Q2 are turned off and on respectively, and a current flows to the TRs Q2 to Q4 and the resistance R12 from the GND. Then the potential of the terminal out is reduced by a degree equal to the voltage VF of the TR Q5 and is set at an L-level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor circuit, and more particularly to an ECL (Emitter Coupled Logic) circuit.

[0002]

2. Description of the Related Art Conventional ECL used for high-speed logic circuits
FIG. 4 shows an example of the circuit configuration of the circuit. Referring to FIG.
In the ECL circuit, the emitter is commonly connected, the base is connected to the input signal VIN and the reference voltage VR, and the collector is directly connected to the higher power supply GND, respectively.
The first and second transistors Q1 and Q2 connected to the higher power supply GND via the resistor R11, the collectors are connected to the commonly connected emitters of the first and second transistors Q1 and Q2, and the base is connected. A third transistor Q3 connected to the reference potential VCS, the emitter of which is connected to the lower power supply VEE via the resistor R12, a collector connected to the higher power supply GND, and a base connected to the collector of the second transistor Q2. And the emitter is connected to the output terminal OUT.
And a fourth transistor Q4 connected to the terminating voltage VT via the resistor 13. The third transistor Q3 and the resistor R12 constitute a constant current source. The fourth transistor Q4 forms an emitter follower.

The operation of the ECL circuit will be described below.

When the input signal voltage VIN is equal to the reference voltage VR
When it is on the higher power supply side, the first transistor Q1 is turned on, the second transistor Q2 is turned off, and the current flows from the higher power supply GND to the first transistor Q1 and the third transistor Q3. , Through the resistor R12. Therefore, since almost no current flows through the resistor R11, the collector potential of the second transistor Q2 rises to the higher power supply potential, and the output potential of the output terminal OUT changes from the higher power supply GND potential to the fourth power supply potential. Transistor Q4
Becomes high level lowered by the forward voltage VF between the base and the emitter.

On the other hand, when the input signal voltage VIN is on the lower power supply side than the reference voltage VR, the second transistor Q2 is turned on, the first transistor Q1 is turned off, and the current is changed to the higher power supply. GND to resistor R1
1, second transistor Q2, third transistor Q
3. Flow through the resistor R12. In this case, if the value of the current flowing through the second transistor Q2 is I and the value of the resistor R11 is R, the collector potential of the second transistor Q2 is (higher-side power supply potential-I × R), and the output terminal OUT The output potential of the fourth transistor Q4 is
The potential is reduced by the forward voltage VF between the emitters.
When this is set to a low level, an ECL circuit having a logical amplitude I × R is obtained.

[0006]

In recent years, miniaturization of devices,
Higher performance has progressed and the breakdown voltage of the junction tends to be lower.
In particular, in a bipolar transistor, the cutoff frequency fT, which is a measure for speeding up, is inversely proportional to the collector-emitter breakdown voltage BVCEO. Therefore, if the cutoff frequency fT of the bipolar transistor is increased in order to increase the circuit speed, the withstand voltage between the collector and the emitter tends to decrease.

On the other hand, in particular, the power supply voltage is invariable in the ECL circuit, and it is becoming difficult to satisfy the guaranteed value of the element destruction with respect to the power supply voltage and the input voltage which is called the absolute maximum rating in the conventional circuit configuration. .

For example, in the circuit shown in FIG. 4, when the input voltage is VIN (provided that VIN is higher than the reference voltage VR), the base-emitter forward voltage of the transistor in FIG. , The emitter voltage of the first transistor Q1, that is, the collector voltage VC of the third transistor Q3 is VC = VIN-VF (1), and the emitter voltage V of the third transistor Q3 is
E is given by VE = VCS-VF (2).

Therefore, the collector-emitter voltage VCE applied to the third transistor Q3 is as follows: VCE = VIN-VCS (3)

Here, assuming that the base voltage VCS of the third transistor Q3 is equal to VEE + 1.2V, from the above equation (3), the collector-emitter voltage VCE of the third transistor Q3 becomes VCE = VIN-VEE-1. .2V (4), and when the input voltage VIN = −0.8 V, the collector
When the emitter breakdown voltage BVCEO is, for example, 3.5 V, the breakdown voltage is exceeded at the lower power supply potential VEE = -5.5 V.

At present, the power supply voltage of the ECL circuit is
In a standard called "ECL-10KH", VEE
= −5.2 ± 5% V in many cases,
When VEE changes by, for example, + 5%, VEE becomes −5.
It becomes 46V, and the voltage VCE between the collector and the emitter of the third transistor Q3 substantially coincides with the withstand voltage between the collector and the emitter.

In some cases, the input voltage VIN rises above -0.8 V, and the margin for the lower power supply potential VEE is further reduced.

As described above, in the conventional ECL circuit,
When the withstand voltage of the transistor becomes small, there is a problem that the same standard as the conventional one cannot be satisfied.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above circumstances, and has as its object to provide a circuit which maintains resistance to a power supply voltage even when a transistor constituting a circuit has a small withstand voltage between a collector and an emitter. Is to provide an ECL circuit which can configure the ECL.

[0015]

In order to achieve the above object, an ECL circuit according to the present invention comprises a common emitter of a switching transistor pair which receives an input signal and a reference voltage, and a constant current source for the switching transistor pair. Another transistor is inserted between the active transistor and the active transistor.

In the present invention, the transistor acting as the constant current source and the another transistor are biased at a base potential at which the voltage between the collector and the emitter is smaller than the breakdown voltage and does not cause saturation. And

Further, the present invention is characterized in that a transistor which is diode-connected between the base of the another transistor and the input terminal of the reference voltage is provided.

Further, in the present invention, it is preferable that a transistor is inserted between the base of the another transistor and a higher power supply terminal, and the base of the inserted transistor is connected to the input terminal of the reference voltage. Features.

[0019]

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

FIG. 1 is a diagram showing the configuration of the first embodiment of the present invention. Referring to FIG. 1, in a first embodiment of the present invention, an emitter is commonly connected, a base is connected to an input signal VIN and a reference voltage VR, respectively, and a collector is directly connected to a higher power supply GND, respectively. First and second transistors Q1 and Q2 connected to a higher power supply GND via a resistor R11, and a collector connected to a commonly connected emitter of the first and second transistors Q1 and Q2; The base is the second reference potential V
A third transistor Q3 connected to CS2, a collector connected to the emitter of the third transistor Q3, a base connected to the reference potential VCS, and an emitter connected to the resistor R1
4, a fourth transistor Q4 connected to the lower power supply VEE, a collector connected to the higher power supply GND, a base connected to the collector of the second transistor Q2, and an emitter connected to the output terminal OUT. And a fifth transistor Q5 connected to the termination voltage VT via the resistor 13.

Next, E according to the first embodiment of the present invention will be described.
The operation of the CL circuit will be described.

When the input voltage VIN is on the higher power supply side than the reference voltage VR, the first transistor Q1 turns on and the second transistor Q2 turns off, so that the current is reduced to the higher power supply GND. The current flows through the first transistor Q1, the third transistor Q3, the fourth transistor Q4, and the resistor R12. Since almost no current flows through the resistor R11, the second transistor Q
2 rises to the higher power supply potential, and the output potential of the output terminal OUT becomes a high level lower than the higher power supply GND potential by the forward voltage VF between the base and the emitter of the fifth transistor Q5. .

On the other hand, when the input signal voltage VIN is on the lower power supply side than the reference voltage VR, the second transistor Q2 is turned on, the first transistor Q1 is turned off, and the current is changed to the higher power supply. GND to resistor R1
1, second transistor Q2, third transistor Q
3, the fourth transistor Q4, and the resistor R12. At this time, if the current value is I and the value of the resistor R11 is R, the collector potential of the second transistor Q2 is (higher power supply potential−I × R), and the output potential of the output terminal OUT is this potential. To the base of the fifth transistor Q5.
The low level is lowered by the forward voltage VF between the emitters.

In the ECL circuit according to the first embodiment of the present invention, the relationship between the lower power supply VEE and VCS2 is
The calculation is specifically described below.

The collector potential V of the third transistor Q3
C3 is a voltage lower than the input voltage VIN by a forward voltage between the base and the emitter of the first transistor Q1 (however, the input voltage VIN is higher than the reference voltage VR).

In FIG. 1, assuming that the forward voltage between the base and the emitter of the transistor is VF, the collector potential VC3 of the third transistor Q3 is VC3 = VIN-VF (5).

Further, the emitter potential VE3 of the third transistor Q3 is as follows: VE3 = VCS2-VF (6)

Therefore, the collector-emitter voltage VCE3 of the third transistor Q3 is given by the following equation (7). VCE3 = VIN−VCS2 (7)

Next, since the collector voltage VC4 of the fourth transistor Q4 has the same potential as the emitter voltage VE3 of the third transistor Q3, VC4 = VCS2-VF (8), and the fourth transistor Q4 Emitter voltage VE4
Is VE4 = VCS-VF (9).

From the above equations (8) and (9), the collector-emitter voltage VCE4 of the fourth transistor Q4 is given by the following equation (10). VCE4 = VCS2-VCS (10)

Therefore, the third and fourth transistors Q3,
Q4 collector-emitter voltages VVE3, VCE4
Is set so as not to be in a saturated state (approximately 0.4 V or less) and not to exceed the withstand voltage.
It is possible to keep the EE possible range, that is, the absolute maximum standard.

For example, assuming that the withstand voltage between the collector and the emitter of the transistor is 3.5 V, 0.4 <VCE3 <3.5 0.4 <VCE4 <3.5 (11) 7) and (10), 0.4 <VIN−VCS2 <3.5 0.4 <VCS2−VCS <3.5 (12)

The reference potential VCS is set to VCS = VEE + 1.
2. When the input voltage is in the range of +0.5 to 1.2 V and the lower power supply voltage VEE is -4.2 to -6.5 V,
The second reference potential VCS2 is -1.8 <VCS2 <-2.6 (13).

If the second reference potential VCS2 is this voltage, the reference voltage VR2 used in the vertical two-stage circuit by the ECL circuit can be used as a supply source of this voltage (transistor The reference voltage VR connected to the base of Q2 is VR1).

FIG. 2 shows the configuration of the second embodiment of the present invention. In FIG. 2, the same or equivalent elements as those in FIG. 1 referred to in the description of the first embodiment are denoted by the same reference numerals. In the following, description of the same parts as in the first embodiment will be omitted, and differences will be mainly described. Referring to FIG. 2, in this embodiment, the sixth embodiment differs from the first embodiment in that a sixth diode-connected transistor Q6 is connected to an input terminal of a reference voltage VR and a third transistor Q6.
Is inserted between the bases of the transistors Q3.

The operation of the circuit of this embodiment is the same as that of the first embodiment.
Of the third transistor Q3
Is connected to the emitter of the sixth transistor Q6, the base and collector of the sixth transistor Q6 are connected to the reference potential VR, and the base potential of the third transistor 3 is changed from the reference voltage VR to the diode VF
By dropping one step, the standard of the second reference potential VCS2 of the first embodiment is satisfied, and a voltage generation circuit and the like for the second reference potential VCS2 are not required.

FIG. 3 shows the configuration of the third embodiment of the present invention. Referring to FIG. 3, in the embodiment of the present invention, the base of third transistor Q3 is connected to the sixth transistor Q3.
, The base of the sixth transistor Q6 is connected to the reference voltage VR, the collector is connected to the higher power supply GND, and the load of the reference voltage VR is the same as that of the second transistor Q6 shown in FIG. 1 / hFE (hFE: current amplification factor) can be reduced as compared with the circuit of the embodiment.

In any of the above embodiments, the third
And the collector, base, and emitter of the fourth transistor Q4 have the same potential. The collector potential of the third transistor Q3 is the same as that of the collector of the third transistor Q3 in FIG. Since the potential is the same as the potential, the effect of the parasitic capacitance of the transistor during operation is the same as that of the conventional example, and the operation speed is not impaired.

[0039]

As described above, according to the ECL circuit of the present invention, even if the withstand voltage between the collector and the emitter of the transistor is reduced, it is possible to form a circuit that maintains the resistance to the power supply voltage. It is effective.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a circuit configuration according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a circuit configuration according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a circuit configuration of a conventional ECL circuit.

[Explanation of symbols]

 Q1 to Q6 Bipolar transistors R11 to R13 Resistance GND High-side power supply VEE Low-side power supply VCS1, VCS2 Reference voltage terminal VIN input terminal OUT output terminal VR reference voltage terminal VT Power supply for terminal termination

Claims (7)

[Claims] An additional transistor is inserted between a common emitter of a switching transistor pair to which an input signal and a reference voltage are input and a transistor acting as a constant current source of the switching transistor pair. ECL circuit. 2. The method according to claim 1, wherein the transistor acting as the constant current source and the another transistor are biased at a base potential such that the collector-emitter voltage is smaller than the breakdown voltage and does not cause saturation. Item 1
The described ECL circuit. 3. The ECL circuit according to claim 1, further comprising a diode-connected transistor between a base of said another transistor and an input terminal of said reference voltage. 4. The device according to claim 1, wherein a transistor is inserted between a base of said another transistor and a higher power supply terminal, and a base of said inserted transistor is connected to an input terminal of said reference voltage. ECL described in 1
circuit. 5. The emitter is connected in common, the base is connected to an input signal and a reference voltage, respectively, and the collector is connected to a higher power supply directly and to a higher power supply via a first resistor, respectively. A first and a second transistor, a third transistor having a collector connected to a commonly connected emitter of the first and second transistors, a base connected to a second reference potential, and a collector A fourth transistor connected to an emitter of the third transistor, a base connected to a first reference potential, and an emitter connected to a lower power supply via a second resistor; and a collector connected to the higher power supply. , The base is connected to the collector of the second transistor, the emitter is connected to the output terminal, and the terminal is connected to the termination voltage via the third resistor. Comprising a fifth transistor, a, ECL circuit, characterized in that to improve the withstand voltage of the circuit. 6. The ECL circuit according to claim 5, further comprising a sixth transistor having an emitter connected to the base of said third transistor, and a collector and a base connected to said reference voltage. 7. A transistor having an emitter connected to the base of the third transistor, a base connected to the reference voltage,
6. The ECL circuit according to claim 5, further comprising a sixth transistor having a collector connected to said higher power supply.