Variable Delay Gate Circuit

The present invention relates to a gate circuit device for adjusting the delay time of an output signal corresponding to an input signal.

A test apparatus for integrated circuits (referred to as an IC tester hereafter) is provided with a number of pins for output signals, from which pins various signals are supplied to integrated circuits in order to check the output condition. In such a case, it is sometimes desired to apply said various signals simultaneously or within in a specified time interval. However, since each circuit generating each of said signals is formed in various manner with different numbers of gates, the time interval in generating each of said signals varies considerably, although the difference is only in order of nanoseconds (ns).

It is therefore the object of the present invention to offer a gate circuit device to output said various signals, in which each logic gate is capable of producing the output with the same time interval by adding a minute adjustment circuit which varies the delay time of the output signals relative to the input signals, that is, of the, signal propagation delay time Tpd, to alter time interval of the output by operation of said minute adjustment circuit.

According to the present invention, there is provided a gate circuit, device comprising a gate circuit having a pair of emitter coupled transistors a constant current source transistor connected to the emitter side of the first transistors, and a terminal which applies a voltage of a predetermined level to a base of said constant current source transistor to control the value of the constant current which said constant current source transistor causes to flow, whereby the signal propagation delay time of said gate circuit is varied to, and settled at, a predetermined value.

According to another feature of the invention, there is provided a gate circuit comprising a gate circuit having a pair of emitter coupled transistors and a constant current source transistor connected to the emitter side of the first mentioned transistors, a control terminal for receiving an externally supplied control current, and a current adjustment circuit means connected to said control terminal and said constant current source transistor, to generate in said constant current source transistor a predetermined current in response to said control current, whereby the signal progapation delay time of said gate circuit is varied to and settled at a predetermined value.

The above and other features of the present invention will become clear from the ensuing descriptions of the preferred embodiments made in reference to the attached drawings, wherein

FIGS. 1 and 3 are the circuit diagrams of two embodiments of the invention;

FIGS. 2 and 4 are graphs showing the operational characteristics of said embodiments;

FIG. 5 is a block diagram of one application of the invention;

FIG. 6 is a circuit diagram of another embodiment of the invention;

FIG. 7 is a graph showing the characteristics of the circuit of FIG. 6; and

FIG. 8 is a circuit diagram of a modified form of the circuit of the invention.

The first embodiment of the invention is shown in FIG. 1 in which emitter coupled transistors Q1 and Q2, a constant current source transistor Q3, and resistors R1 to R3 constitute an emitter coupled logic (ECL) circuit. Transistor Q8 constituting a constant current source and a resistor R4 form a load for an output emitter follower transistor Q4. Vi denotes input the voltage to the logic gate circuit formed by the above-described components, Vr the reference voltage,f Vo the output voltage, and Vs the voltage that determines the value of the constant current. Reference voltage Vr is a threshold voltage for determining the high (H) and low(L) states of the input voltage Vi, and, when Vi is high relative to Vr, the transistor Q1 turns on and the transistor Q2 is turned off, and the output Vo is at the high state, and when Vi is low relative to Vr, the transistor Q1 turns off, the transistor Q2 is turned on, and the output voltage Vo is at the low state.

In the above circuit, the output voltage Vo lags a certain length of time relative to the input voltage Vi, but this delay time is constant depending upon the value of the current. To adjust the current in this circuit, an additional emitter follower circuit comprising the transistors Q5 to Q7, the transistor Q9 and the resistor R5 is connected in parallel to an output emitter follower circuit Q4, Q8, R4 of the output level, with the additional emitter follower circuit functioning as a load capacitor, thus controlling the value of the current flowing in said load circuit Q8, Q9 by virtue of the control voltage Vc that is applied to a terminal T1. The control voltage Vc is externally applied to the device 1 by a digital/analog converter DAC from which a constant voltage is applied by the dividing resistors R8, R9.

The transistors Q5 to Q7 are connected parallel, their bases being connected to an output terminal of the ECL circuit together with the base of transistor Q4. By this arrangement, the base capacitance of the transistors Q5 to Q7 is connected to the output terminal of the ECL circuit, and the delay time Tpd increases. The base capacitance of the transistors Q5 to Q7 varies depending on the value of the current flowing through each of these transistors, but since the transistor Q9 regulates by means of control voltage Vc the value of the total currents flowing in the transistors Q5 to Q7, the base capacitor of each of the transistors Q5 to Q7 is regulated by the control voltage Vc, and consequently the delay time Tpd is made adjustable by an external control voltage Vc. Further, since the control voltage Vc is also applied to the base of the transistor Q8, the value of the current at the output terminal is also regulated by the control voltage Vc, so that the delay time Tpd is made adjustable.

When the control voltage Vc is set in a high state to increase the current through the transistors Q8, Q9, the working of the emitter follower circuit becomes rapid and the delay time Tpd is decreased. Contrary to this, when the control voltage Vc is lowered to decrease the current through the transistors Q8, Q9, the working of the emitter follower circuit slows down and the delay time Tpd is increased.

FIG. 2 shows the relationship of the control voltage Vc relative to the signal propagation delay time Tpd, in which the axis of the abscissa represents the control voltage Vc in volts, the axis of the ordinate is the signal propagation delay time Tpd in nanoseconds. The dotted curve C2 shows the delay characteristic when there is only one transistor Q8 with transistors Q5 to Q7 and Q9 omitted, and curve C1 shows the delay characteristic with the load circuit including Q5 to Q7, Q9, R5. When the number of the transistors Q5, Q6 . . . is increased, the load capacitor increases accordingly and thus the delay time Tpd increases. In the above circuit, the control voltage Vc is commonly applied to the transistor Q8 of the output level of the emitter follower circuit and the transistor Q9 of the load circuit. However, if the control voltage Vc is applied independently to the transistors Q8, Q9, a finer adjustment of the delay time will be realized.

Further, by adding the load circuit Q5 to Q7, as shown in FIG. 2, the range of delay time Tpd, which varies in accordance with the control voltage Vc, becomes large to make possible delay time adjustments with a higher degree of precision.

In another embodiment, the delay time Tpd may be adjusted by regulating the voltage Vs applied externally of the device 1 to a terminal T2 connected to the base of the constant current transistor Q3 of the ECL circuit comprising transistors Q1, Q2. That is, when Vs is increased, the ECL circuit works at a high speed to decrease delay time Tpd, and on the other hand, if Vs is decreased, the ECL circuit works at a low speed to increase the delay time Tpd.

Thus, the delay time Tpd may be changed by either regulating the voltage Vc to the terminal T1 or by regulating the voltage Vs to the terminal T2, and it is possible to regulate both voltages simultaneously or to regulate either one or both independently.

FIG. 3 shows an other embodiment of the invention, in which the same components as those shown in FIG. 1 are designated by the same reference numbers. The transistors Q11, Q21 and the resistor R11, the transistors Q12, Q22 and the resistor R12, and the transistors Q13, Q23 and the resistor R13 provide respective emitter follower circuits respectively, transistors Q21 to Q23 forming respective constant current sources thereof. In other words, the emitter follower of FIG. 1 is replaced by three levels of emitter followers connected consecutively, with the control voltage Vc being commonly applied to the constant current transistors Q21 to Q23 and to the base of the constant current source transistor Q3.

In this circuit, when the current of transistors Q3 and Q21 to Q23 is increased by increasing the control voltage Vc, the working speed of both the ECL circuit and of the emitter follower circuit becomes high to decrease the delay time Tpd. When the control voltage Vc is lowered, the reverse takes place.

FIG. 4 shows the delay characteristics of said circuit. Curve C11 represents the delay characteristic when the entire circuit is regulated by the control voltage Vc, and the dotted curve C12 shows the characteristic when the ECL circuit alone is so regulated. This shows that, by regulating the constant current transistors Q21 to Q23 of the emitter follower simultaneously, rather than by regulating only the base potential of the constant current transistor Q3 of the ECL circuit, the delay time Tpd may be increased more than when the control voltage Vc is lowered in the same manner. Further, it shows that, by providing several levels of emitter follower, the entire delay time Tpd is, increased, that is a high precision adjustment of the delay time Tpd becomes possible by regulating the control voltage Vc. It may also be arranged in said circuit so that either one or both of transistors Q3 and transistors Q21 to Q23 may be regulated independently.

FIG. 5 illustrates an application of the circuit of the invention to an IC tester in which various signals are generated at generator 10 having groups of input terminal pins 12, output terminal pins 14 and control terminal pins 16, respectively. Each pin 14 is connected to an integrated circuit (IC) 11 to be tested. The circuit of the invention is employed in an output gate group G3, in an input gate group G1 or in an internal gate group G2. The number of the circuits of the invention as shown in FIG. 1 or FIG. 3 is the same as the number of output terminal pins 14. According to the present invention, the circuit in FIG. 1 or 3 is the output gate of the group G3. There is provided a controller 20 comprising the control circuit CNT having counter means which measures the difference in time of the input and output signals for each input and output terminal pin, that is, the delay time Tpd, which serves as an operation circuit to calculate the delay time to be added that is necessary to equalize the delay time Tpd for all the output terminal pins, a table in memory MEM in which is stored the digital control voltage Vc for each output terminal pin, and a digital/analog converter DAC which converts the digital control voltage to an analog voltage. The number of the digital/analog converters DAC equals the number of the output termial pins, and the register means MEM is provided at the input of the converters DAC to provide the memory read out data, so that, in testing integrated circuits, a control voltage Vc for each terminal pin is output from each digital/analog converter DAC. A circuit to generate a designated control voltage Vc may be provided to each side of the terminal pins, that is, to the circuit of FIG. 1 or FIG. 3, to provide only one digital/analog converter DAC in FIG. 5 to which the control voltage Vc of each terminal pin is output, with said control voltage Vc being output to each of said voltage generating circuits. If the delay of the output level gate circuit of FIG. 1 and FIG. 3 is made constant, the measurement of the above delay time Tpd and the determination of the control voltage Vc are done only once, thus making it possible to output from said IC tester various test voltages correctly and at the same time.

The test signal generator 10 and the controller 20 may be fabricated in one LSI or in individual ICS. Where they are fabricated in each IC device individually, the terminal T which receives the control voltage Vc becomes an external terminal pin of an IC in the test signal generator.

In the embodiments of the invention so far described, the adjustment of the delay time is effected by applying a control voltage to either the constant current transistor of the current switch circuit or to the base of the constant current source transistor of the emitter follower circuit. Because of this, the current in either the current switch circuit or the emitter follower circuit in response to the change of the control voltage does not change linearly. Thus, in a certain range of control voltage, the ratio of change of current is too large, and in another range of the control voltage, said ratio is too small. Where the base potential is regulated, it is difficult to set a range of the current change to be sufficiently wide. Further, it is desired to minimize the error in setting the value of the current due to variation of the control voltage and the resistance of the wirings.

In the delay circuit, it is therefore desired to regulate the base current of the transistor placed in the emitter follower circuit, so that current in the emitter follower circuit changes linearly in response to the control voltage.

The second embodiment of the invention is shown in FIG. 6 in which the circuit comprises a current switch circuit having emittr coupled transistors Q31, Q32, transistor Q33 for a constant current circuit and resistors R21, R22, R23, R24, an emitter follower circuit having transistors Q34, Q35 and resistor R25, a control current supply circuit having a PNP type transistor Q37, resistors R27, R28, R29, a control current supply circuit having a digital/analog converter DAC and a series circuit of the transistor Q36 connected between the base of the current control transistor Q35 of the emitter follower circuit and the resistor R26. The part with reference numeral 30 is an integrated circuit device, for example, which is arranged to receive the externally-supplied current I.sub.CNT through its terminal 40. An input signal V.sub.IN is supplied to the base of the transistor Q31 of the current switch circuit, i.e. ECL circuit, and the reference voltage V.sub.BB is applied to the base of the transistor Q32. The bias voltage V.sub.CS generated internally or externally is applied to the base of the transistor Q33 of the constant current circuit.

In the circuit of FIG. 6, when the input signal V.sub.IN is higher than the reference voltage V.sub.BB, the transistor Q31 turns on with the transistor Q32 turned off, and the low level output signal V.sub.OUT is obtained from the emitter of the transistor Q34. Contrary to this, when the voltage of the input signal V.sub.IN is lower than the reference voltage V.sub.BB, the transistor Q31 is turned off with the transistor Q32 turned on, and the output signal V.sub.OUT is at the high level voltage.

On the other hand, the digital control signal D.sub.IN input to the digital/analog converter DAC is converted to an analog voltage in said converter DAC and is applied to the base of the transistor Q37 via the resistor R29. The control current I.sub.CNT corresponding to said analog signal flows to the collector of the transistor Q37, which current flows via the external terminal 40 to the bases of the transistor Q35 and transistor Q36, thus constituting a base current adjustment circuit CONT.

Now, where transistors Q35 and Q36 have the same characteristics, there is a relationship as follows:

where I.sub.EF is the emitter current of the transistor Q35 and is equal to the current of the emitter follower circuit. Further, I.sub.M is the current of the current adjustment circuit CONT. That is, it becomes possible to adjust linearly the current of the emitter follower circuit, comprised of the transistors Q34, Q35 and the resistor R25, by the control current I.sub.CNT. Also, the current adjustment circuit CONT, comprising the transistor Q36 and the resistor R26, is in a current mirror relationship to the emitter follower circuit relative to the control signal.

As explained above, by adjusting the external control current I.sub.CNT in response to the control signal D.sub.IN, and by causing the current I.sub.EF of the internal emitter follower circuit to vary, it becomes possible to adjust the signal propagation delay time of said emitter follower circuit and to adjust different delay times between the input signal V.sub.IN and the output signal V.sub.OUT.

FIG. 7 shows one example of the delay time Tpd between the input signal V.sub.IN and the output signal V.sub.OUT relative to the control current I.sub.CNT.

In the circuit of FIG. 6, the delay time is adjusted by varying the current of the emitter follower circuit by means of the control current, and it will be clear that adjustment of the delay time is possible also by adjustment of the current in the current switch circuit. In this case, it is enough if the control current I.sub.CNT is sent to the base of the current source transistor Q33 in the circuit of FIG. 6. Further, the current of the emitter follower circuit and the current of the current switch circuit may be adjusted together.

In other words, in the ECL circuit as shown in FIG. 8, any one of currents I.sub.EF1 and I.sub.EF2 of the emitter follower circuits and current I.sub.CS of the current switch circuit may be adjusted, or each of said currents, at respective points may be adjusted simultaneously. In such a case, the transistor of each current source forms a current mirror circuit together with the base current adjustment circuit C.sub.CNT such as the one shown in FIG. 6. Further, in FIG. 8, the current switch circuit comprises the transistors Q38, Q39 and resistors R30, R31 and the constant current circuit I.sub.CS, the transistor Q40 and the constant current circuit I.sub.EF1 form the first emitter follower circuit, and the transistor Q41 and the current source circuit I.sub.EF2 form the second emitter follower circuit. Further, each of the current source circuits I.sub.CS, I.sub.EF1, I.sub.EF2 may comprise a transistor and a resistor respectively in the same manner as the circuit of FIG. 6, in which case the control current I.sub.CNT is supplied to the base of each transistor. In this case again, the current source circuit I.sub.M corresponds to the base current adjustment circuit in the circuit of FIG. 6.

As explained, the first embodiment has the technical effect that, by adding a circuit for adjusting the signal propagation delay time Tpd to the logic gate circuit, a simultaneous output of each signal is realized using said gate circuit at the output level. In the second embodiment, current in the current switch circuit, or in the emitter follower circuit, is adjusted by the current supplied from the control current generating circuit with said control current generating circuit, being formed as a current source circuit, and the current of the current switch circuit, or the current of the emitter follower circuit, is linearly varied relative to the control signal. Because of this, the delay time of the circuit is correctly and easily adjusted. Further, since the delay time is adjusted by the control current, there is no effect from the resistance of the wirings and the unevenness of the base voltage in setting up the delay time.