Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2003-03-06
2004-08-10
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S056000, C327S061000
Reexamination Certificate
active
06774680
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a comparator for comparing an input signal with a reference voltage. More specifically, the present invention is directed to a comparator for comparing an analog signal having a wide range of an input voltage, to a LSI test system for testing electric characteristics of an IC, and also to an apparatus which requires a comparison/judgement of voltage levels.
Conventionally, in this sort of the comparator, an allowable input voltage range for an input signal relative to a reference voltage is determined based upon a breakdown voltage V
EBO
between a base and an emitter of a differential transistor pair (namely, reverse-voltage application range of V
BE
). When a reverse voltage applied across a base and an emitter of a transistor is increased, a current amplification factor h
FE
is lowered. In general, a reverse voltage between a base and an emitter of a bipolar transistor under which no reduction of a current amplification factor h
FE
is caused, is on the order of about 2 to 3 V, namely low voltage. A maximum voltage which can be applied across a base and an emitter of a transistor without lowing the factor h
FE
will be referred to as a base-emitter reverse withstanding voltage V
R
hereinafter.
In other words, an input voltage range which does not deteriorate characteristics of a comparator circuit is determined by the base-emitter reverse withstanding voltage V
R
of a transistor, and thus, there is such a problem that a voltage difference across an input table input voltage and a reference voltage is small.
FIG. 4
indicates an example of the most generic differential type comparator circuit with employment of a differential transistor pair. An input signal Vin is inputted to an input terminal
20
, and a reference voltage Vref is entered to another input terminal
21
of this differential type comparator circuit. Both a transistor
1
N and another transistor
2
N are turned ON/OFF in response to a high/low relationship of voltage levels of the input signal Vin and the reference voltage Vref. A current I
0
of a current source
6
flows through either a resistor
8
or a resistor
9
, thereby producing a voltage drop and thus outputting a comparison judgement level (H/L) to output terminals
22
and
23
.
FIG. 5A
to
FIG. 5C
represent conditions of changes in base-emitter voltages V
BE
of the transistors
1
N and
2
N in such a case that an input signal Vin
20
is changed with time, and is compared with a certain reference voltage Vref
21
. Until the present time reaches time t
1
(in case of input signal Vin
20
<reference voltage Vref
21
), the transistor
1
N is turned OFF and the transistor
2
N is turned ON. When the present time exceeds the time t
1
(in case that input signal Vin
20
>reference voltage Vref
21
), the transistor
1
N is turned ON and the transistor
2
N is turned OFF. As to a reverse voltage applied across a base and an emitter of a transistor set under OFF state, assuming now that a voltage across a base and an emitter of such a transistor set under ON state is equal to V
BE(ON)
, a voltage of input signal Vin
20
−reference voltage Vref
21
−V
BE(ON)
is applied. If the ON-voltage V
BE(ON)
between the base and the emitter is neglected, then a difference between the input signal Vin
20
and the reference voltage Vref
21
is applied as the reverse voltage across the base and the emitter of the transistor set to the OFF state (see
91
of
FIG. 5B and 92
of FIG.
5
C). While a base-emitter reverse withstanding voltage V
R
of a bipolar transistor is about 2 to 3 V, namely a low voltage, an input voltage range which does not deteriorate the characteristic of the comparator is determined based upon the reverse withstanding voltages V
R
of the transistors
1
N and
2
N. As a result, there is such a drawback that the input signal can be compared with the reference voltage only when a difference between the input signal and the reference voltage is 2 to 3 V in maximum.
Conventionally, JP-A-2-69016 has described a technique of such a comparator for aiming an enlargement of a voltage range for an input signal.
FIG. 6
shows a similar circuit diagram to this conventional comparator. In this comparator circuit, a voltage dividing circuit
37
constituted by a plurality of resistors is inserted into a prestage of a comparator
103
.
FIG. 7A
to
FIG. 7D
show voltage levels Vin′
200
, and Vref′
211
inputted to the comparator
103
, and conditions of changes in voltages V
BE
applied across the bases and the emitters of the transistors
1
N and
2
N in the case that the input signal Vin
20
is changed with time, and is compared with a certain constant reference voltage Vref
21
. As indicated in
FIG. 7B
, as the voltages Vin′
200
and Vref′
211
inputted to the comparator
103
, such voltages are entered which are produced by reducing the original input signal Vin
20
and the original reference voltage Vref
21
by a resistance ratio (voltage dividing ratio) of the voltage dividing circuit
37
provided at the prestage of this comparator
103
. Since the resistor values of the voltage dividing circuit
37
are determined in such a manner that the resistor values do not exceed reverse withstanding voltages V
R
between the bases and the emitters of the transistors
1
N and
2
N in consideration of the input voltage range of the input signal Vin and the reference voltage Vref, the enlargement of the input voltage range is realized.
With the arrangement of the voltage dividing circuit
37
at the prestage of the comparator
103
, however, a low-pass filter (LPF) is undesirably constituted by stray capacitances of both the transistors
1
N and
2
N, and both the resistors
95
and
96
of the voltage dividing circuit
37
. As a consequence, there is such a problem that high frequency components of the input signal are cut off by the low-pass filter LPF, and thus, the input band width of the comparator
103
is restricted.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a comparator capable of enlarging a voltage range of an input signal, and capable of directly comparing/judging a voltage level of the input signal with respect to a voltage level of a reference voltage.
Another object of the present invention is to provide a comparator which is especially suitable for a LSI test system for testing ICs.
To achieve the above-described objects, typical inventive comparators among comparators according to the present invention are as follows:
According to one aspect of the invention, a comparator is comprised of: a pair of transistors which are continuously brought into ON states; wherein: switch means constructed of a diode pair, for switching a current path in response to a high/low relationship between a voltage level of an input signal and a voltage level of a reference voltage; and means for converting the current into a voltage level are provided between emitter terminals of the transistor pair.
According to another aspect of the invention, a comparator is comprised of: an input terminal having a diode; a differential transistor pair in which the transistors are turned ON/OFF in response to a high/low relationship between a voltage level of an input signal and a voltage level of a reference voltage; a circuit constituted by a diode between base terminals of the differential transistor pair; and means for converting the current which is switched by the differential transistor pair into a voltage level.
According to still another of aspect of the invention, a comparator is comprised of: a differential transistor pair which is turned ON/OFF in response to a high/low relationship between a voltage level of an input signal and a voltage level of a reference voltage; diodes each provided at the emitter terminal of the differential transistor pair and diodes each provided between the emitter and the base of the differential transistor pair; and means for c
Arita Kaoru
Chujo Norio
Imagawa Kengo
Imanari Masahiro
Umemura Yoshiharu
Antonelli Terry Stout & Kraus LLP
Callahan Timothy P.
Hitachi , Ltd.
Luu An T.
LandOfFree
Comparator including a differential transistor pair and a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Comparator including a differential transistor pair and a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Comparator including a differential transistor pair and a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3329354