Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-06-06
2001-09-25
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S065000, C327S077000
Reexamination Certificate
active
06294949
ABSTRACT:
This patent application claims priority based on a Japanese patent application, H11-160082 filed on Jun. 7, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage drive circuit, a voltage drive apparatus and a semiconductor-device testing apparatus. More particularly, the present invention relates to a voltage drive circuit generating voltage in accordance with an input signal, a voltage drive apparatus including the voltage drive circuit, and a semiconductor-device testing apparatus including the voltage drive circuit and the voltage drive apparatus.
2. Description of the Related Art
Among a test list for testing a semiconductor-device, there are a lot of test items related to an operational margin of the semiconductor-device, which is a device under test and will be simply referred to as a DUT hereinafter. In order to secure the performance conditions for the DUT that the DUT is operated under, which is a power voltage ranging between 3 volt±10%, a semiconductor-device testing apparatus for testing the DUT needs to test the DUT using an input signal having same range of the voltage as the performance conditions of the DUT under the power voltage of that range. Considering an input signal A having a voltage of 3 volts, the semiconductor-device testing apparatus is required to output the input signal A with a maintained logic value, but shifted voltage to between 2.7 volts to 3.3 volts. Therefore, a voltage drive circuit that outputs the input signal A as varying voltage should be incorporated.
FIG. 1
shows a structure of a conventional voltage drive circuit
10
. The input signal A is generated by a pulse generator P
1
as a differential signal. The input signal A can take two values including a high value whose logic value is one, and a low value whose logic value is zero. When the input signal A is high, it means that the input signal A takes the high value, a positive output P
1
p from the pulse generator P
1
becomes high and a negative output P
1
m becomes low. The positive output P
1
p of the pulse generator P
1
is connected to a base of the transistor Q
1
, and the negative output P
1
m of the pulse generator P
1
is connected to a base of the transistor Q
2
. Thus, when the input signal A is high, the transistor Q
1
is switched on and the transistor Q
2
is switched off. When, on the other hand, the input signal A is low, the transistor Q
1
is switched off and the transistor Q
2
is switched on. As the voltage drive circuit
10
is constructed such that either of the transistors Q
1
and Q
2
is switched on when the other of the transistors Q
1
and Q
2
is switched on, the current flowing in the voltage drive circuit
10
can be kept constant. Thus, the variation of the power voltage of the circuit
10
can be reduced and the circuit
10
can be operated at high-speed.
An emitter of the transistor Q
1
and an emitter of the transistor Q
2
are connected to a current drive circuit iG
1
that generates a constant current i. A collector of the transistor Q
1
and a collector of the transistor Q
2
are connected to a constant voltage source VG
1
respectively via the resistance R
1
and the resistance R
2
. The constant voltage source VG
1
generates a voltage VH. In this circuit
10
, the signal is output from an output point
12
located between the resistance R
2
and the transistor Q
2
, as an output voltage Vout. The output signal maintains its logic value, but has the output voltage Vout which is different from that of the input signal A.
In the above structure, the transistor Q
2
is switched on when the input signal A is low, and the constant current i flows through the resistance R
2
. At this time, the output voltage Vout becomes Vout=VH−i*R
2
(formula 1). On the other hand, the transistor Q
2
is not switched on when the input signal A is high, and the constant current i flows through the transistor Q
1
. At this time, the output voltage Vout becomes Vout=VH (formula 2). As described above, the input signal A can take two values including high and low. Thus, the output voltage of the input signal A can be varied in accordance with either of the formulas 1 and 2 which are obtained depending on the values of the input signal A.
However, due to recent developments in semiconductor techniques, performances of semiconductor-devices are highly advanced. Thus, the semiconductor-device testing apparatus needs to have precise performance.
As for the circuit
10
shown in
FIG. 1
, for example, a base current ib is actually input to the base of the transistor Q
2
and thus the actual output voltage Vout does not match the value obtained in accordance with the above formula 1. The base current is a nonlinear function depending on voltage between the collector and the emitter, and a collector current. Furthermore, the base current can easily be affected by errors caused during manufacturing. Thus, it is difficult to adjust the circuit by the base current ib taking into consideration.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a voltage drive circuit, a voltage drive apparatus and a semiconductor-device testing apparatus capable of precisely setting an output voltage which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a voltage drive circuit generating a voltage in accordance with an input signal, comprises: an output voltage generator including: a current drive circuit having a current adjustable terminal; an output voltage generating transistor being switched on and off in accordance with the input signal; an output voltage generating resistance through which a current flows when the output voltage generating transistor is in a first operational state and being switched on; and an output point where an output voltage which is shifted from a predetermined voltage is generated by a voltage drop caused at both ends of the output voltage generating resistance; and an output voltage monitor including a comparator comparing the shifted output voltage with a predetermined expected voltage, wherein an output from the comparator is connected to the current adjustable terminal of the current drive circuit.
The output voltage monitor may include a reference voltage generating circuit generating a reference voltage whose ratio to the shifted output voltage is a predetermined value, and the comparator may compare the reference voltage with the expected voltage.
The reference voltage generating circuit may include: a reference current drive circuit, a reference transistor being switched on and off and capable of being in a predetermined operational state; and a reference resistance through which a current flows, the current flows through the reference current drive circuit via the reference transistor.
The reference transistor may have a structure such that current flowing therethrough is 1/k (k is a positive real number) times as large as current flowing through the output voltage generating transistor, when both of the reference transistor and the output voltage generating transistor are switched on, and the reference resistance may have a resistance value which is k times as large as a resistance value of the output voltage generating resistance.
The reference current drive circuit may have a current adjustable terminal, and an output of the comparator may be connected to the current adjustable terminal of the reference current drive circuit.
The first operational state for the output voltage generating transistor and the predetermined operational state for the reference transistor may be such that both of the transistors are switched on or both of the transistors are switched off, and the reference voltage may become equal to the shifted output voltage when the outpu
Kojima Shoji
Sekino Takashi
Advantest Corporation
Pillsbury & Winthrop LLP
Tran Toan
LandOfFree
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