Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-09-22
2002-04-30
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06381054
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical pulse transmission system and an optical pulse transmitting method which permit high-speed transmission of electric signal pulses after converting them into optical pulses. The present invention also pertains to a waveform converting method advantageous for use at the transmitting side for conversion of the electric signal pulses to optical pulses and a light intensity modulator advantageous for use at the transmitting side for the modulation of light, and an optical pulse detecting method advantageous for use at the receiving side for the detection of the optical pulses transmitted thereto.
BACKGROUND ART
Many of semiconductor device testing apparatus (commonly called IC testers) for testing various semiconductor devices, including semiconductor integrated circuits (ICs), for instance, employ a semiconductor device transporting and processing or handling apparatus (commonly called a handler) which transports semiconductor devices for testing and sorts out tested semiconductor devices based on the test results. In the semiconductor device testing apparatus of the type that has the semiconductor device transporting and processing or handling apparatus (hereinafter referred to as handler) connected thereto, a test head for applying a test signal of a predetermined pattern to a semiconductor device under test (commonly called DUT) is placed in a test section of the handler away from the main body (tester proper) of the semiconductor device testing apparatus. The test head and the tester proper are connected via an electric signal transmission line such as a cable, through which the test signal of a predetermined pattern is fed from the tester proper to the test head, and the test signal is applied to the semiconductor device under test via a socket mounted on the test head. A response signal from the semiconductor device under test is sent over the electric signal transmission line from the test head to the tester proper for measuring electrical properties of the semiconductor device.
In recent years, semiconductor integrated circuits (hereinafter referred to as ICs) are becoming faster and the number of terminals (pins) mounted on the package is also on the increase. As a result, the transmission of an electric signal over a transmission line such as a cable as in the above-mentioned semiconductor device testing apparatus will cause such defects as listed below.
(1) With the use of the cable or similar electric wire, there is a limit to the frequency of the electric signal for transmission therethrough, and an increase in the signal frequency is likely to cause the degradation of the signal waveform. This imposes severe limitations on the signal transmission rate, making it difficult to test fast-acting ICs.
(2) Cables now in use are so thick that an increase in the number of cables with an increase in the number of IC terminals will inevitably make thick, heavy and hence hard-to-handle the bundle of cables between the tester proper and the test head.
As a solution to the above-mentioned problems, an optical transmission system has recently come into use which is excellent in the signal transmission rate and in the frequency characteristic as compared with the above-mentioned electric transmission system and is capable of employing, as its transmission medium, an optical fiber or like transmission line which is thin and light. Next, a common optical transmission system will be described.
For the generation of a binary digital signal (optical pulses) by modulating light, a light intensity modulation system which changes the intensity of light according to an information signal (a modulation signal) is used in most instances because of simplicity of the modulation techniques involved. Usually, the light intensity modulation system has a configuration in which a laser diode capable of fast light intensity modulation is provided as a light emitting device at the transmitting side, a fast-response photodiode is provided at the receiving side and an optical fiber is used as a transmission medium; optical pulses emitted from the laser diode at the transmitting side are sent over the optical fiber to the receiving side, where the optical pulses sent thereto are converted by the photodiode to electric signals.
FIG. 23
is circuit diagram schematically depicting an example of a conventional optical transmission system using an optical transmission line. The illustrated optical transmission system comprises an optical pulse transmitting device
101
, an optical pulse receiving device
102
, and an optical transmission line
109
, such as an optical fiber, for interconnecting the transmitting device
101
and the receiving device
102
.
The optical pulse transmitting device
101
is provided with a main circuit
103
for outputting an electric pulse signal to be sent to the receiver side, a driving circuit
104
connected at its input terminal to an output terminal
103
A of the main circuit
103
, and a semiconductor laser or similar light emitting device
105
connected between the output terminal of the driving circuit
104
and a common conductor. The light emitting device
105
responds to an electric pulse signal fed thereto from the driving circuit
104
to emit light and hence generate optical pulses, which are provided via an optical connector
109
A onto the optical transmission line
109
for transmission to the optical pulse receiving device
102
.
The optical pulse receiving device
102
comprises a photodiode or similar photodetector
106
, a detecting circuit
107
connected at its input terminal to the output terminal of the photodetector
106
, and a main circuit
108
connected at its input terminal to the output terminal of the detecting circuit
107
; the optical pulses sent over the optical transmission line
109
are input into the photodetector
106
via an optical connector
109
B. The photodetector
106
converts the received optical pulses to an electric pulse signal, and applies it to the detecting circuit
107
. The detecting circuit (usually formed by a current-to-voltage converting amplifier)
107
detects the electric pulse signal fed thereto and provides it to the main circuit
108
. The main circuit
108
performs various processes based on the electric pulse signal input thereto.
In general, a laser diode is used as the light emitting device
105
, but as is well-known in the art, the laser diode has a defect that the quantity of light emitted therefrom varies with a temperature change.
FIG. 24
shows injected current vs. output light power characteristics of the laser diode. In
FIG. 24
the curve A indicates the injected current vs. output light power at a temperature T
1
(° C.) and the curve B the injected current vs. output light power at a temperature T
2
(° C.) (where T
1
<T
2
).
As is evident from
FIG. 24
, current values I
ON1
and I
ON2
for driving the laser diode to emit light vary with ambient temperature. As a result, if a driving current I
D
of the same peak value as the above-mentioned current values is used to drive the light emitting device
105
by the driving circuit
104
, the light emitting device
105
outputs an optical pulse OP
1
at the temperature T
1
(° C.) and an optical pulse OP
2
at T
2
(° C.) as depicted in FIG.
24
.
As will easily be understood from
FIG. 24
, an ambient temperature variation will cause a change in the power of the optical pulse that is output from the light emitting device
105
. Hence, in the case of receiving the optical pulses OP
1
and OP
2
by the optical pulse receiving device
102
, optical pulse waveforms, which cross a threshold voltage EC for detecting the reception of the optical pulses, lag in timing according as peak values of the received signals are large or small, as indicated by &Dgr;t
1
and &Dgr;t
2
in FIG.
25
. This entails a disadvantage that the temperature variation is sent as jitter to the receiving device
102
.
A real-world example in which the generation of jitter is disadvantageous can be found, for example
Kishi Nobuhito
Okayasu Toshiyuki
Advantest Corporation
Chan Jason
Gallagher & Lathrop
Lathrop, Esq. David N.
Sedighian M. R.
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