JPS6123415A - Ecl-ttl level converting circuit - Google Patents

Abstract

PURPOSE:To obtain an output waveform without dependancy of a power supply voltage by holding a base current when an output transistor (Tr) is turned on to a constant value even if the power supply voltage is fluctuated. CONSTITUTION:A common emitter is brought into a constant voltage by inputting an output of emitter follower Trs Q3, Q6 receiving an operating output of an emitter coupling logical circuit comprising Trs Q1, Q2 to each base of Tr pairs Q7, Q8. The said constant voltage and a constant current circuit comprising Trs Q9, Q10 of diode connection are used to bias a TrQ11. A base current IB when the output TrQ5 is turned on is obtained from the difference between current I1 and I2, where I1 is a current flowing to the resistor R5 at input H level and I2 is a collector current of the TrQ11 and the relation of IB=VBE/R9 is obtained and the circuit is immune to the effect of a power supply voltage. Thus, even if the power supply voltage is fluctuated, the depth of the saturation of the TrQ5 is kept constant and a stable output waveform is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an ECL-CL using bipolar transistors.
The present invention relates to a TTL level conversion circuit, particularly an ECL-TTL level conversion circuit that is capable of stable output without depending on power supply voltage.

[Prior Art] An example of a conventional ECL-TTL level conversion circuit is shown in FIG.

The emitter-coupled logic circuit consisting of the transistor pair Q1Q2 is a constant current source I. The output signal is level-shifted by a diode through the emitter follower Q3, and the output signal is TTL-driven.
Input to the level conversion circuit.

The TTL level conversion circuit includes a transistor Q4 and a resistor R1.
Resistors R5 and R made up of R6 and output transistor Q
The output transistor Q5 is driven by the signal divided by 6.

Such a circuit operates when the input terminal IN is at the “H” level or “L” level.
Depending on the level, the output transistor Q5 is turned "ON" or "OFF" to obtain an output converted to a TTL level.

[Problem to be solved by the invention] Here, the output transistor Q5 is 110 N I+
The base current IB at the time of input 11 is the current ■1' flowing through the resistor R at the HIT level and the current ■2 flowing through the resistor R6.
It is expressed as the difference between

1 = T'−'l ” −(V −RI −3V, E) /R5C10 −V 8./R6 In addition, ■ is the constant current, R1, R5, and R6 are the resistors R,
The resistance values of R5 and R6, Vcc is the power supply voltage, and VB[ is the voltage between the base and emitter of the transistor.

As is clear from the above equation, the base current I8 has dependence on the power supply voltage vcc.

Therefore, when the power supply voltage fluctuates, the output transistor Q5
There was a problem in that the depth of saturation changes and the output waveform also changes.

[Means for Solving the Problems] An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an FCL-TTL level conversion circuit whose output waveform does not change depending on the power supply voltage.

That is, the gist is that the output of a current switching type logic circuit consisting of a pair of transistors having a common emitter is
In the circuit for converting to L level, the outputs of the emitter followers connected to the outputs of each of the above transistor pairs are input to the bases of the collector-emitter common transistor pairs, and a resistor and a diode are sequentially connected to the common emitters of the transistor pairs. A resistor is connected to the emitter of a transistor connected to one output of the emitter follower, and the other end of the resistor is connected to the base of an output transistor and a transistor biased by the constant current circuit. The ECL-TTL level conversion circuit is characterized in that it is configured by connecting the collectors of the ECL-TTL level converter.

[Embodiment] FIG. 1 shows an embodiment of the ECL-TTL level conversion circuit of the present invention, and the same parts as in FIG. 2 are designated by the same reference numerals.
The explanation will be omitted here.

First, an emitter follower Q1Q6 receives the operational output of an emitter-coupled logic circuit consisting of transistors Ql and Q2.
By inputting the output of Q7 to the base of each of the transistor pair Q7, 0.8, their common emitters are made to have a constant voltage.

Next, a constant current circuit is constructed with this constant voltage, resistor R9, and diode-connected transistor Q9''10, and transistor Q11 is biased.
The collector current 12' of No. 11 is expressed by the following equation.

12= = (Vo,,-R,I o-4V2C) /
R9·(1) On the other hand, the current 11 flowing through the resistor R5 when the input 11 is at HII level is given by the following equation. .

1l-(VoC-R1Io-3■8F)/R5...(
2) Here, the output transistor Q5 is “ON”.
Since the base current (2)8 at the time is expressed by the difference between the current 11 flowing through the resistor R5 and the collector current (2) of the transistor Q11, the following equation is obtained from equations (1) and (2).

■8-11-■2' = (1/R5-1/R9) (V, o-RoI.

-3V) 10V8E/R9 B[ Now, if the resistance values of resistors R5 and R9 are made equal, ■ -■
8E/R9, and is not affected by the power supply voltage.

Therefore, even if the power supply voltage fluctuates, the saturation depth of the output transistor can be kept constant, and a stable output waveform can be obtained.

[Effects of the Invention] As explained above, according to the present invention, the dependence of the power supply voltage can be reduced by keeping the base current constant when the output transistor is "ON" even if the power supply voltage fluctuates. It is possible to obtain an output waveform free of □, and its industrial value is extremely great.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the ECL-TTL level conversion circuit of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional ECL-TTL level conversion circuit. 01-Q11: Transistor R1-R9: Resistor Io:
Constant current source 11: Current I flowing through resistor R5: Resistor R
Current I' flowing through transistor Q11: Rector current I of transistor Q1: Base current of transistor Q5

Claims (1)

[Claims] (1) In a circuit that converts the output of a current switching type logic circuit consisting of a transistor pair having a common emitter to a TTL level, the output of an emitter follower connected to the output of each of the transistor pairs is converted to a transistor pair having a common collector and emitter. a resistor and a diode are sequentially connected to the common emitter of the transistor pair to form a constant current circuit, and a resistor is connected to the emitter of the transistor connected to one output of the emitter follower,
An ECL-TTL characterized in that the base of an output transistor and the collector of a transistor biased by the constant current circuit are connected to the other end of the resistor.
Level conversion circuit.