JPH0685661A - Ecl output circuit - Google Patents

Abstract

PURPOSE:To provide an output voltage temperature fluctuation reduction circuit for an ECL output circuit in which the increment of power consumption is small. CONSTITUTION:The output of a transistor differential amplifier 1 is buffered by emitter-follower transistors 2, 3, and output voltages are generated at terminating resistors 4, 5. Transistors 8, 9 for temperature compensation which permit an in-phase current I1 to flow are connected to the load resistors 6, 7 of the amplifier 1. Resistors 10, 11 (with resistance value R2) are connected to the emitters of the transistors 8, 9, respectively, and a diode 12 and a current source 13 which supplies a bias current I2 to the diode are connected to the base. Temperature fluctuation of I1XR1 is set in a direction opposite to that in the temperature fluctuation in voltage drop by transistors 2, 3, and also, the output voltage temperature fluctuation of the ECL output circuit can be decreased by making the absolute value of the fluctuation coincide or approach.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ECL (emitter coupled logic) output circuit used in a high speed digital circuit.

[0002]

2. Description of the Related Art In the prior art, the temperature characteristic of the output voltage of an ECL output circuit composed of a transistor differential amplifier and an emitter follower transistor is determined by the temperature variation of the base-emitter voltage of the output emitter follower. Has a coefficient. In a high-speed digital circuit, the temperature fluctuation of the output voltage causes a decrease in the phase margin due to the amplitude-phase conversion, which causes performance deterioration such as the maximum operating frequency. As a method for compensating the temperature variation of the base-emitter voltage, a temperature compensation diode and a resistor are connected between the transistor differential amplifier load resistors shown in FIG. Is used to reduce the output temperature fluctuation by utilizing the temperature coefficient of the forward voltage of the temperature compensating diode. However, since the current flowing between the differential transistor load resistors flows in the direction of decreasing the output amplitude, the current flowing through the transistor differential amplifier must be increased in order to obtain the same output amplitude, which results in a large power consumption. was there.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to realize an output voltage temperature fluctuation reducing circuit for an ECL output circuit which consumes less power.

[0004]

SUMMARY OF THE INVENTION The above-mentioned object is to allow a current sufficient to generate a voltage for compensating the temperature variation of the base-emitter voltage of an emitter follower transistor from the outside to the load resistance of the transistor differential amplifier. It is realized by. Since this current flows in the same phase direction with respect to the load resistance of the differential transistor, the output amplitude is not reduced. Also,
The magnitude of the current is small with respect to the entire load current (several mA) flowing through the load resistance of the differential transistor, and the amount of increase in power consumption is smaller than that of the conventional technique.

[0005]

The diode for supplying a constant current is connected to the base of the temperature compensating transistor, and the current generated by the difference between the temperature compensating transistor and the forward voltage of the diode is supplied to the transistor differential amplifier. To load resistance. The temperature coefficient of the transistor base-emitter voltage is determined by the emitter current of the transistor. In the case of transistors having the same structure, the larger the emitter current density, the smaller the absolute value of the temperature coefficient. The same applies to the forward voltage of the diode. Therefore, if the element size of the transistor and the diode is changed to change the current density, a specific temperature coefficient difference can be set. Instead of changing the emitter size,
The same applies when a plurality of transistors and diodes of the same size are connected in parallel. This temperature coefficient difference is converted into a current by using the resistor connected to the emitter of the temperature compensation transistor, and further by the load resistance of the transistor differential amplifier,
If converted into a voltage, it is possible to reduce the temperature fluctuation of the output voltage of the emitter follower transistor.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

The output of the transistor differential amplifier 1 is buffered by the emitter follower transistors 2 and 3 to generate an output voltage at the terminating resistors 4 and 5. In-phase current I1 is applied to load resistors 6 and 7 (resistance value R1) of the transistor differential amplifier.
The temperature compensating transistors 8 and 9 are connected. Resistors 10 and 11 (resistance value R2) are connected to the emitters of the temperature compensating transistors 8 and 9, respectively, and a diode 12 is connected to the base and a current source 13 for supplying a bias current I2 to the diode is connected.

As for the temperature coefficient of the output voltage Vo, the temperature fluctuation of the load current Io of the transistor differential amplifier 1 and the base currents of the emitter followers 2 and 3 can be ignored.

[0009]

## EQU00001 ## dVo / dT = -R1.times. (DI1 / dT)-(dVbe2 / dT) If the base currents of the transistors 8 and 9 are ignored.

[0010]

## EQU00002 ## dI1 / dT = [(dVf12 / dT)-(dVbe8 / dT)] / R2

[0011]

## EQU00003 ## dVo / dT =-(R1 / R2) .times. ((DVf12 / dT)-(dVbe8 / dT)]-(dVbe2 / dT) where Vbe2, Vbe8, and Vf12 are the bases of the transistors 2 and 8, respectively. -The voltage between the source and the emitter and the forward voltage of the diode 12 are shown. On the other hand, the relationship between I1 and I2 is VT = k × T / q = 26 mV (k: if the ratio of the emitter sizes of the transistor 8 and the diode 12 is 1: n).
Boltzmann constant, T = 300K: absolute temperature, q: electron content)

[0012]

4 is given by I1 = ln (n × I2 / I1) × VT / R2.

Normally, the temperature coefficient of the transistor base-emitter voltage and the diode forward voltage is negative (approximately -1 to-
2 mV), the absolute value is smaller as the current flowing through the transistor and the diode is larger. Therefore, from Equation 4, n × I
If 2 / I1> 1, it is possible to select a value at which the first term and the second term on the right side of Equation 3 cancel each other.

As an example, R1 = 200Ω, R2 = 30
Ω, I1 = 0.09 mA, I2 = 0.67 mA, n = 1
6

[0015]

## EQU00005 ## dVo / dT =-(200/30) .times. ((-1.4 mV / .degree. C.)-(-1.6 mV / .degree. C.)]-(-1.35 mV / .degree. C.) = 0.016 mV / .degree. The output voltage temperature fluctuation can be reduced to about 1/80. At this time, if the ECL circuit output amplitude Vop is set to about 0.8V, the transistor differential amplifier load current Io becomes

[0016]

(6) Io = Vop / R1 = 0.8V / 200Ω = 4mA >> I1 and I2, and the increase in power consumption is small.

[0017]

According to the present invention, it is possible to realize an ECL output circuit whose output voltage is stabilized against temperature fluctuations. The increase in power consumption is also small. Further, according to this circuit, since it is not necessary to connect the load resistances of the differential transistors, mutual interference between the differential transistors can be prevented, and the effect of reducing the output waveform distortion of the ECL output circuit operating at high speed can be obtained. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a circuit according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transistor differential amplifier, 2, 3 ... Emitter follower transistors, 4, 5 ... Termination resistors, 6, 7 ... Load resistors, 8, 9 ... Temperature compensation transistors, 10, 11 ... Resistors,
12 ... Diode, 13 ... Current source.

Claims (1)

[Claims] 1. A transistor differential amplifier, an emitter follower transistor, a temperature compensating transistor for supplying a current to the transistor differential amplifier load resistor, and a resistor connected to the emitter of the temperature compensating transistor.
The transistor differential amplifier load composed of a diode connected to the base of the temperature compensating transistor and a current source for supplying a bias current to the diode, the transistor differential amplifier load being generated by the collector current of the temperature compensating transistor. The temperature variation of the voltage drop of the resistor is opposite to the temperature variation of the voltage drop due to the emitter follower transistor, and the absolute values thereof are the same or close to each other.
CL output circuit.