Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Analysis of complex waves
Reexamination Certificate
2001-07-30
2003-09-02
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Analysis of complex waves
C324S096000
Reexamination Certificate
active
06614214
ABSTRACT:
BACKGROUND OF THE INVENTION
The maximum frequency of signals in electrical and electronic devices has continued to increase in recent years. Devices that handle signals up to 100 GHz now exist. The increasing use of electro-optical devices, such as those used in optical communication and optical memory, has contributed to this increase in maximum frequency. Such advances in device performance have given rise to the need to provide a corresponding increase in the maximum frequency of apparatus used to observe and measure the waveforms of high-speed and high-frequency signal waveforms.
One way to observe the waveform of a high-speed or high-frequency electrical signal is to sample the electrical signal. Sampling the electrical signal converts the electrical signal to a lower-speed electrical signal that can be observed and measured conventionally. The broadest-band sampling oscilloscope currently commercially available has a bandwidth of only 50 GHz. Various approaches have been tried in an attempt to produce a sampling oscilloscope with a broader bandwidth. Some of the proposed approaches, and their drawbacks, will be described next.
One approach is described by K. Takeuchi and A. Mizuhara in
Scanning Tunneling Optoelectronic Microscope with
2
Ps Time Resolution,
32 ELEC. LETT., 1709-1711 (1996 August). This approach uses a photoconductive switch as a sampling element. A photoconductive switch is controlled by light generated by a commercial pulsed light source having a full width at half maximum of about 100 fs. The electrical signal-under-test is sampled by passing it through the photoconductive switch. The photoconductive switch easily provides a response having a full width at half maximum of about 2 ps. A sampling circuit that uses such a photoconductive switch as its sampling element can respond with a time resolution of 2 ps, which corresponds to a frequency of about 175 GHz.
Photoconductive switches tend to have a dynamic switching characteristic that exhibits a tailing response in its turn-off characteristic, as will be described in more detail below. As a result of this, a sampling device that incorporates a photoconductive switch as its sampling element has frequency characteristics that are not flat at low frequencies, and the response of the sampling device gradually decreases with increasing frequency. Such characteristics are not desirable in a sampling device for high-frequency and high-speed electrical signals.
Another approach is described by Wesley C. Whitely et al. in 50
GHz Sampler Hybrid Utilizing a Small Shockline and an Internal SRD
, AA-6 IEEE MTT-S DIGEST, 895-898 (1991). In this approach, a high-speed step signal is generated by a step recovery diode (SRD). The fall-time of the high-speed step signal is reduced by passing the signal through a non-linear transmission line (NLTL). After passing through the NLTL, the high-speed step signal is applied as a sampling pulse to a diode sampling bridge.
FIG. 1
is a block diagram of the sampling circuit
10
disclosed by Whitely et al. In the sampling circuit
10
, the output of the local oscillator
12
is applied to a step recovery diode
14
. The step signal generated by the step recovery diode is converted into a balanced step signal by the microstrip balun
16
. The balanced step signal is fed by the coplanar line
18
to the non-linear transmission line
20
. The non-linear transmission line is composed of a high-impedance transmission line with shunt varactor diodes placed at intervals along its length. The non-linear transmission line can be regarded as having N identical stages. Each stage contains a varactor diode centered in a length d of transmission line. An exemplary one of the varactor diodes is shown at
22
. Passing the step signal through the NLTL decreases the fall time of step signal generated by the step-recovery diode
14
.
The output of the NLTL
20
is connected by the coplanar lines
24
, composed of the striplines
25
and
26
, to the sampling signal inputs of the sampling chip
27
. The step signal output by the NLTL propagates through the coplanar stripline
28
, composed of the signal line
29
and the ground lines
30
and
31
. After passing through the coplanar stripline
29
, the step signal is reflected by the short-circuit at the input port
32
to form a sampling pulse.
The hold capacitor
40
is connected in series with the sampling diode
42
, and the termination resistor
36
is connected in parallel with the series combination. The resulting series/parallel combination is connected between the signal line
29
and the junction of the strip line
25
and the ground line
30
. The hold capacitor
44
is connected in series with the sampling diode
46
, and the termination resistor
38
is connected in parallel with the series combination. The resulting series/parallel combination is connected between the signal line
29
and the junction of the strip line
26
and the ground line
31
.
The signal-under-test SUT is received at the input port
32
and is fed to the connection point of the sampling diodes
42
and
46
by the signal line
29
. The signal-under-test is sampled by the sampling diodes. The samples are held by the hold capacitors
40
and
44
. The IF signal composed of the samples of the signal-under-test is coupled from the junction of the hold capacitor
40
and the sampling diode
42
and from the junction of the hold capacitor
44
and the sampling diode
46
via the hold resistors
48
and
50
and the low-pass circuitry
52
and
54
. The IF signal is processed by a suitable IF amplifier (not shown).
The non-linear transmission line
20
is composed of at least ten stages each composed of a high impedance transmission line and a shunt varactor diode. The example described by Whitely et al. had
27
stages. The NLTL therefore imposes a large insertion loss on the high-speed step signal, which makes it difficult to generate large-amplitude sampling pulses for application to the sampling diodes
42
and
46
. This causes the sampling device
10
to generate the IF signal with an insufficient signal-to-noise ratio for some applications. Moreover, the non-linear circuit elements included in the NLTL can cause multiple reflections in the NLTL. The reflected signals appear superimposed on the high-speed step signal and increase the rise- and fall-times of the sampling pulses. As a result, the narrowest sampling pulse achieved had a full width at half maximum of about 10 ps. This limits the maximum frequency of the signal-under-test that can be sampled by the sampling device
10
.
A sampling device in which an air gap between the signal line and the substrate is introduced into the non-linear transmission line
20
is disclosed by S. T. Allen in
Schottky Diode Integrated Circuits for Sub
-
Millimeter
-
Wave Application
, PH.D. DISSERTATION, UNIVERSITY OF CALIFORNIA, SANTA BARBARA (1994 June). The air gap reduces the insertion loss and enables the sampling device to sample a signal-under-test with a maximum frequency as high as 725 GHz. Thus, the sampling device can sample a signal-under-test with a higher maximum frequency, but its complex structure results in a high manufacturing cost.
Accordingly, what is needed is a way to generate very short electrical sampling pulses with fast rise- and fall-times, and to generate such sampling pulses at low cost. What is also needed is to provide a sampling device that uses such sampling pulses.
SUMMARY OF THE INVENTION
The invention provides a sampling element that comprises a DC sampling voltage source, a threshold sampling circuit and a photoconductive switching element. The threshold sampling circuit includes a signal-under-test input, a sampling pulse input and an IF signal output, and has a sampling threshold with respect to sampling pulses received at the sampling pulse input. The photoconductive switching element is connected between the DC sampling voltage source and the sampling pulse input of the threshold sampling circuit.
The invention also provides a sampling device that comprises a DC sampling voltage
Kaneko Yasuhisa
Mizuhara Akira
Takenaka Tsutomu
Yamada Norihide
Agilent Technologie,s Inc.
Benson Walter
Hardcastle Ian
Le N.
LandOfFree
Sampling element controlled by photoconductive... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sampling element controlled by photoconductive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sampling element controlled by photoconductive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3104732