Spectrum analyzer having means for displaying spectrum data together with power value thereof

A directing section substantially directs an input signal to first and second paths. A signal processing section outputs spectrum data corresponding to the input signal directed to the first path. A power detecting section detects a power value corresponding to the input signal directed to the second path. A display section displays the power value together with spectrum data.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a spectrum analyzer and, more particularly, to an 
improvement of a spectrum analyzer for analyzing an RF frequency or 
optical signal. 
2. Description of the Related Art 
As is well known, a spectrum analyzer measures the characteristics of a 
high-frequency signal within a relatively wide range; for example, within 
several tens of kHz to several hundred GHz, and displays the spectrum 
intensity at each frequency on a CRT display section, as a function of 
frequency. As is shown in FIG. 10, such a spectrum analyzer includes, for 
example, an RF section (high-frequency circuit) 1, an IF section 
(intermediate-frequency circuit) 2, a detecting section 3, an A/D 
converting section 4, a digital memory 5, a CRT display section 6, a sweep 
signal generating section 7, a data processing and control section 8, and 
the like. 
With the above circuit arrangement, a high-frequency input signal 
to-be-measured a, input from an input terminal 9, is input to the RF 
section 1 consisting of a mixer and a local oscillator. In the RF section 
1, the input signal a is mixed with a local signal whose frequency is 
changed in accordance with the signal level of a sweep signal b output 
from the sweep signal generating section 7. Thus, the signal a is 
frequency-converted into an intermediate-frequency signal c which is 
output from the RF section 1 and input to the IF section 2 which 
incorporates a bandpass filter (BPF). Only a frequency component which 
coincides with the pass frequency of the bandpass filter passes through 
the IF section 2, is input to the detecting section 3, and output as a DC 
detection signal d corresponding in strength to the magnitude of the input 
frequency component. The detection signal d is then converted into digital 
data by the A/D converting section 4, in response to the period of a 
sampling signal e output from the data processing and control section 8 
consisting of, for example, a microprocessor. Thereafter, the converted 
data is stored in the digital memory 5 consisting of, for example, a RAM. 
In response to a read signal f output at a predetermined period from the 
data procesing and control section 8, digital data of the detection signal 
d for each sampling period, stored in the digital memory 5, is read out in 
a predetermined order, and supplied to the display section 6. The display 
section 6 includes an image memory for one frame which can be displayed on 
a display screen at one time. After sequentially input data values are 
stored in the image memory, image data read out from the image memory for 
one frame is displayed on the display screen. Thus, spectrum distribution 
data is displayed on the display screen of the display section 6, as shown 
in FIG. 11. 
Each spectrum shown in FIG. 11 has an ideal linear shape. However, each 
spectrum having a width corresponding to a bandwidth of the bandpass 
filter in the IF section 2 is actually displayed. 
The above-mentioned data processing and control section 8 controls the 
sweep interval and sweep speed of the sweep signal generating section 7, 
outputs the sampling signal e to the A/D converting section 4, and outputs 
the read signal f to the digital memory 5, so that spectrum distribution 
data as shown in FIG. 11 is displayed on the display section 6. In 
addition, the data processing and control section 8 executes a calculation 
required for display, on the display section 6, of the spectrum value 
corresponding to the desired frequency value. 
The spectrum analyzer having the above arrangement shown in FIG. 10 has, 
however, the following problems. In order to examine the characteristics 
of signal a, accurate distribution data relating to the spectrum values at 
every frequency contained in the signal a must be obtained, and the total 
value of the spectrum values, i.e., the power value of the input signal to 
be measured a must be simultaneously obtained, in many cases. 
When the input signal a contains spectrum components distributed over the 
bandwidth of the bandpass filter in the IF section 2, its power value is 
measured, as follows, using the conventional spectrum analyzer as shown in 
FIG. 10. Data values obtained for every period of the sampling signal e in 
the A/D converting section 4 during a period from the start to the finish 
of one sweep signal b can be integrated by, for example, the data 
processing and control section 8. Accurate integration of the power value 
of the input signal a is based on the assumption that the spectrum values 
within the entire frequency range of signal a are accurately measured. 
However, it is generally difficult to predict in advance the distribution 
of the spectrum components contained in the input signal to be measured. 
In addition, as described above, when a deviation of the spectrum to be 
measured, corresponding to the bandwidth of the bandpass filter in the IF 
section 2, is corrected and the integration is performed, complicated 
correcting calculation is required. Therefore, it is practically 
impossible to accurately measure the power value by the above integration 
method. 
In such a spectrum analyzer, only signal components within the specific 
frequency sweep range selected and set by the data processing and control 
section 8 are displayed on the display section 6. Actually, high-level 
spectrum values (frequency components) are often present in a frequency 
region outside the frequency sweep range. Thus, an operator is often 
unaware of the high-level frequency components. In addition, saturation in 
the RF section 1 is neglected, and many measurement errors may be caused. 
Furthermore, the RF section 1 may be damaged due to excessive input. In 
particular, when a signal such as a noise signal and an RF pulse signal 
wherein spectra are distributed in a wide range is measured, the power 
value and pulse peak power are further increased as compared with each 
spectrum value. Therefore, the above-mentioned problems tend to occur. 
Even if all the spectra are present in the pass band of the bandpass filter 
in the IF section 2, as in the case of continuous-wave (CW) signal and the 
power value can be measured in principle, a considerable error is usually 
generated because the signal to be measured passes through the complicated 
signal circuits 7 in the RF and IF sections 1 and 2. Therefore, in an 
attempt to accurately measure the power value of the continuous-wave 
signal, a signal having well-known accurate power value is input in 
advance as a reference signal, and an indication value of the spectrum 
analyzer is calibrated for the frequency to be used. However, the 
calibration process is quite time-consuming and the efficiency of 
measurement operation is considerably degraded. In practice, it is almost 
impossible always to provide a signal source having a well-known accurate 
power value at a measurement frequency, and the power value must be 
measured with an insufficient measurement precision. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a new and 
improved spectrum analyzer which distributes a signal to-be-measured 
between a signal processing section and a power detector through a signal 
branching section, in order to obtain an accurate reading of the power 
value of the signal, for display together with the usual spectrum 
distribution data. 
According to one example of the present invention, there is provided a 
spectrum analyzer comprising: 
directing means for substantially directing an input signal to a first path 
and a second path; 
data-producing means for producing spectrum data corresponding to the input 
signal directed to the first path by the directing means; 
sensing means for sensing a power value corresponding to the input signal 
directed to the second path by the directing means; and 
display means for displaying the spectrum data produced by the 
data-producing means, together with a power value sensed by the sensing 
means. 
The spectrum analyzer according to the above example is able to obtain an 
accurate power value, for display together with the usual spectrum 
distribution data, without the measuring time being increased. 
The spectrum analyzer according to another example of the present 
invention, comprises: 
an RF section for mixing a signal to-be-measured input from an input 
terminal, with a local oscillation signal frequency-swept in response to a 
sweep signal from a sweep signal generating section, and 
frequency-converting the mixed signal; 
an IF section for extracting a predetermined frequency component of an 
output signal from the RF section; 
a detecting section for detecting an output signal from the IF section; an 
A/D converting section for converting a detection signal from the 
detecting section into a digital value, at a predetermined period; 
a CRT display section for displaying each digital value converted by the 
A/D converting section as a spectrum value at each frequency; 
a signal branching circuit located between the input terminal and the RF 
section; and 
a power detector for detecting the power value of the signal to-be-measured 
branched by the signal branching circuit and supplying the power value to 
the display section in order to display the power value together with the 
spectrum value. 
In the spectrum analyzer having the above arrangement, the signal 
to-be-measured, input to the input terminal, is input to the RF section 
and to the power detector through the signal branching circuit. The signal 
to-be-measured input to the RF section is converted into a spectrum value 
corresponding to each frequency by the RF section, the IF section, the 
detecting section, and the A/D converting section, and is displayed on the 
display section. 
On the other hand, the power value of the signal to-be-measured input to 
the power detector is detected as a mean value or a peak value by the 
power detector. The detected power value is then displayed on the display 
section, together with each spectrum value. 
A spectrum value at each frequency and the power value of the signal to be 
measured are displayed on the CRT display section at the same time. 
A spectrum analyzer according to still another example of the present 
invention, comprises: 
a signal processing section for processing a signal to-be-measured, input 
from an input terminal, in response to a sweep signal, and outputting a 
signal corresponding to a spectrum of the signal to-be-measured; 
a first A/D converting section, for converting the corresponding signal 
into first digital data; 
a first memory, for storing the first digital data; 
a signal branching/switching circuit located between the input terminal and 
the signal processing section; 
a power sensor for detecting the power of the signal to-be-measured output 
from the signal branching/switching circuit; 
a second A/D converting section, for converting an output from the power 
sensor into second digital data; 
a second memory, for storing an output from the second A/D converting 
section; and 
a display section for displaying the second digital data together with the 
first digital data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A general description the present invention will be now be presented, prior 
to more detailed ones of the preferred embodiments thereof. As shown in 
FIG. 1, the present invention pertains to a spectrum analyzer comprising a 
signal processing section 101 for processing a signal to-be-measured input 
from an input terminal IN in response to a sweep signal input from a sweep 
signal generating section 100, and outputting a signal corresponding to 
the spectrum of the signal to-be-measured, a first A/D converting section 
102 for converting the corresponding signal into first digital data, a 
first memory 103 for storing the first digital data, and a display section 
104 for displaying the first digital data. 
According to the present invention, there is provided a spectrum analyzer 
comprising a power sensor 106 for detecting the power of the signal 
to-be-measured input through a signal branching circuit (or a signal 
switching circuit) 105 located between the input terminal IN and the 
signal processing section 101, a second A/D converting section 107 for 
converting an output from the power sensor 106 into second digital data, a 
second memory 108 for storing an output from the second A/D converting 
section 107, and having a specific arrangement characterized in that the 
second digital data is displayed on the screen of the display section 104 
together with the first digital data. 
According to the present invention, in addition to the above-mentioned 
specific arrangement, there is provided a spectrum analyzer comprising a 
correction data detecting unit 109 for detecting, as correction data, a 
difference between the first digital data stored in the first memory 103 
and the second digital data stored in the second memory 108, a third 
memory 110 for storing correction data, which represents the difference 
between the first and second digital data detected by the correction data 
detecting unit 109, and a correcting unit 111 for correcting the first 
digital data stored in the first memory on the basis of the correction 
data, and displaying the resultant corrected data on the display section 
104. Referring to FIG. 1, the correction data detecting unit 109, the 
third memory 110, and the correcting unit 111 are arranged in a data 
processing and control section 112 similar to that shown in FIG. 10. 
According to the present invention, there is provided, in addition to the 
above-mentioned specific arrangement, a spectrum analyzer comprising a 
common A/D converting section 102 provided as the first and second A/D 
converting sections 102 and 107, and a switching section 113 for switching 
and supplying a signal from the power sensor 106 to the common A/D 
converting section 102 so as to control the switching section 113 in 
synchronism with a sweep period and a reset period of the sweep signal. 
The first and second memories, 103 and 108, should, incidently, be 
understood as being individual memory areas within a single memory. 
According to the present invention, there is additionally provided a 
spectrum analyzer comprising a variable attenuator 114, arranged between 
the signal branching circuit 105 and the signal processing section 101, 
for varying an input level to control the attenuation value of the 
attenuator to be a desired value, on the basis of the second digital data. 
In this way, an excessive input level can be reduced to a proper level. 
Embodiments of the present invention based on the above general description 
will now be described hereinafter, with reference to the accompanying 
drawings. 
FIG. 2 is a block diagram showing a schematic arrangement of a spectrum 
analyzer according to a first embodiment. The same reference numerals in 
FIG. 2 denote the same parts as in the conventional spectrum analyzer 
shown in FIG. 10. In this embodiment, a signal branching circuit 11 is 
arranged between an input terminal 9 and an RF section 1 including a mixer 
1a and a local oscillator 1b. The RF section 1 is connected to one output 
terminal of the signal branching circuit 11, through the variable 
attenuator 114 and a power detector 12 is connected to the other output 
terminal thereof. The signal branching circuit 11 consists of a resistive 
power divider, for example, and distributes a signal to-be-measured a 
input from the input terminal 9 to the RF section 1 and the power detector 
12, at a power distribution ratio (e.g., 1:1) determined earlier in 
accordance with a voltage division ratio of the resistor. 
The power detector 12 consists of a normal high-frequency power detector 
employing a thermocouple element, a diode element, an averaging circuit, 
and the like, or a power detector utilizing a wide-band amorphous power 
sensor technique. The power detector 12 can accurately detect the power 
value of a signal within a wide range of DC frequency to high frequency. 
As the latter amorphous power sensor, a power detector described in U.S. 
patent application No. 216,909, and EPC application No. 87906936.7 filed 
or assigned by the present applicant or assignee, can be used. A DC power 
value signal g output from the power detector 12 is input to an A/D 
converting section 4 via a switching circuit 13. The switching circuit 13 
receives a detection signal d output from a detecting section 3. The 
switching circuit 13 switches to supply the detection signal d or the 
power value signal g to the A/D converting section in response to a 
switching signal h output from a data processing and control section 8'. 
A digital memory 5' has first and second memory areas corresponding to the 
first and second memories 103 and 108 shown in FIG. 1. 
The arrangement of the RF section 1, IF section 2, detecting section 3, A/D 
converting section 4, display section 6, and sweep signal generating 
section 7 as shown in the embodiment of FIG. 2 is the same as that shown 
in FIG. 10. However, as will be described later, the control for each unit 
of the data processing and control section 8' shown in FIG. 2 differs from 
that of FIG. 10. 
A variable attenuator 114 which is the same as that shown in FIG. 1 is 
controlled by the data processing and control section 8'. 
The operation of the spectrum analyzer having the above arrangement will 
now be described below, with reference to a timing chart of a general 
sweep signal b output from the sweep signal generating section 7, as shown 
in FIG. 3. Specifically, at time t0, the sweep signal b for sweeping the 
frequency of a local oscillation signal i, output from the local 
oscillator 1b in the RF section 1, starts an increase from a minimum value 
corresponding to the minimum measurement frequency. After a sweeping 
period A has elapsed, i.e., at time t1, and the signal b reaches a maximum 
value corresponding to the maximum measurement frequency, the signal level 
is decreased. After a reset period B has elapsed, i.e., at time t2, the 
signal b starts sweeping in the next sweeping period A from the minimum 
value corresponding to the original minimum measurement frequency. 
During the sweeping period A, the data processing and control section 8' 
outputs the switching signal h to the switching circuit 13, to supply the 
detection signal d to the A/D converting section 4, whereas during the 
reset period B, section 8' outputs signal h to circuit 13, to supply the 
power value signal g to section 4. 
Thus, during the sweeping period A, the high-frequency signal 
to-be-measured a is input from the input terminal 9 to the mixer 1a in the 
RF section 1, is mixed with the local oscillation signal frequency-swept 
in response to the sweep signal b, and the resultant mixed signal is 
converted into an intermediate-frequency signal c. In the IF circuit 2, 
only a frequency component of the signal c output from the RF section 1, 
which coincides with the pass frequency of a bandpass filter (BPF) is 
extracted to be input to the detecting section 3, where it is converted 
into a DC detection signal d corresponding in strength to its magnitude, 
and input to the A/D converting section 4 via the switching circuit 13, is 
converted into digital data in accordance with a period of a sampling 
signal e output from the data processing and control section 8' by the A/D 
converting section 4, and stored in the first memory area of the digital 
memory 5'. 
In response to a read signal f output from the data processing and control 
section 8' at a predetermined period, the digital data for every sampling 
period of the detection signal d, stored in the first memory area of the 
digital memory 5', are read out in a predetermined order, and supplied to 
the display section 6. As a result, as is shown in FIG. 4, the spectrum 
value at each frequency, i.e., spectrum distribution data D1, is displayed 
on the display section 6. Note that this spectrum distribution data is 
held until the next reset period B ends. 
During the reset period B, the power value signal output from the power 
detector 12 is converted to a digital value by the A/D converting section 
4 via the switching circuit 13, and the digital value is stored in a 
second memory area in the digital memory 5', provided as an exclusive 
storing region of the power value. Thereafter, the value is read out from 
the digital memory 5', and displayed in an empty area of the 
above-mentioned spectrum distribution data in the CRT display section 6 as 
a mean power value Pl, in a numerical value character data form, as shown 
in FIG. 4. The numerical value character data of the power value is held 
until the next sweeping period A ends. 
In this manner, the spectrum distribution data and the power value are 
displayed on a single screen of the display section 6, as shown in FIG. 4. 
The signal branching circuit 11 and the power detector 12 are arranged so 
that a spectrum value at each frequency and a total power value of the 
signal to-be-measured a can be obtained at the same time. 
As described above, the signal branching circuit 11 and the power detector 
12 of the present invention are simple in arrangement, and thus can be 
manufactured at low cost. In addition, they can have wide-range frequency 
characteristics. Therefore, a considerable increase in manufacturing cost 
can be suppressed, as compared with the conventional spectrum analyzer 
shown in FIG. 10. 
The measurement precision of the spectrum analyzer according to the present 
invention can be greatly improved as compared with the case wherein 
spectrum values are added to calculate the power value. 
In the first embodiment, shown in FIG. 2, the power value is measured by 
utilizing the reset period B of the sweep signal b. Therefore, upon the 
measurement of the power value, the total measuring time is not prolonged 
as compared with the conventional spectrum analyzer for obtaining only 
spectrum distribution data. In other words, the power value can also be 
measured within the conventional measuring time. 
FIG. 5 is a block diagram showing a spectrum analyzer according to a second 
embodiment of the present invention. The reference numerals in FIG. 5 
denote the same parts as in the first embodiment shown in FIG. 2. 
In the second embodiment, an RF (high-frequency) switching circuit 11a is 
used as a signal branching circuit located between an input terminal 9 and 
an RF section 1. In response to a switching signal h output from a data 
processing and control section 8', the RF switching circuit 11a can switch 
whether a signal to-be-measured a, input from the input terminal 9, is 
supplied to the RF section 1 or to the power detector 12. This switching 
timing is synchronized with that of the switching circuit 13. 
More specifically, in a sweeping period A of a sweep signal b shown in FIG. 
3, the data processing and control section 8' switches the RF switching 
circuit 11a to the RF section 1 side and switches the switching circuit 13 
to the detection signal d side by the switching signal h. During the reset 
period B, the data processing and control section 8' similarly switches 
the RF switching circuit 11a to the power detector 12 side, and the 
switching circuit 13 to the power value signal g side. 
Each spectrum value is measured during the sweeping period A, and the power 
value is measured during the reset period B. Therefore, in the second 
embodiment, the spectrum distribution data and power value of the signal 
to-be-measured a can both be measured at the same time, and displayed on a 
single screen of the display section 6. As a result, the same effect as in 
the first embodiment can be obtained. 
By using the RF switching circuit 11a as the signal branching circuit, the 
loss of the signal to-be-measured can be suppressed as compared with other 
signal branching circuits employing the above-mentioned resistive power 
divider or a directional coupler. As a result, a reduction in sensitivity 
of the entire spectrum analyzer caused by insertion of the signal 
branching circuit can be prevented. 
FIG. 6 is a block diagram showing a spectrum analyzer according to a third 
embodiment of the present invention. The reference numerals in FIG. 6 
denote the same parts as in FIG. 2. 
In the third embodiment, a switching circuit 13 in FIG. 2 is eliminated, 
and a detection signal d output from a detecting section 3 is directly 
input to an A/D converter 4. In addition, a power value signal g output 
from a power detector 12 is input to another A/D converter, 4a. Digital 
data obtained by the A/D converters 4 and 4a are written in first and 
second memory areas in a digital memory 5', respectively. It should be 
noted that although, in this embodiment, the same sampling signal e is 
input to the A/D converters 4 and 4a, it always need not be the same 
sampling signal e. 
With the above arrangement, the spectrum distribution data and the power 
value of the signal to be measured a also can be obtained. Therefore, the 
same effect as in the first embodiment in FIG. 2 can be obtained. 
In the third embodiment, since the detection signal d and the power value 
signal g are converted into digital data values by means of exclusive A/D 
converters 4 and 4a, respectively, the power value also can be measured 
during the sweeping period A as shown in FIG. 3. Therefore, even if the 
sweeping period A for measuring the spectrum is long, the power value of 
the input signal to be measured a can be monitored on the display screen 
of the display section 6 in real time. Thus, the power value of the signal 
to-be-measured a can be monitored not only during the reset period B, but 
also during sweeping period A, i.e., the power value can always be 
monitored. Therefore, when an overpower is input, an alarm output is 
immediately generated to produce an alarm display or an alarm sound. In 
addition, in the same manner as in FIG. 2, the power value signal a can be 
utilized to automatically adjust an attenuation level of an input 
attenuator 114 located at a previous portion of the RF section 1 and 
obtain a correct display value. In other words, this spectrum analyzer can 
be free from damage due to an excessive signal input. 
In the above embodiments shown in FIGS. 2, 5, and 6, in accordance with a 
specific operation (calibration command CALIB) of an operation section OP, 
the data value can be calibrated by the data processing and control 
section 8' in order to display a correct data value obtained from the 
signal to-be-measured a on the display section 6, by using a calibration 
signal for which an accurate relationship between the detection signal d 
and the power value g is obtained in advance. Note that, in this case, 
when a continuous-wave (CW) signal is used as the calibration signal, its 
power value need not be known in advance. 
In this case, the data processing and control section 840 can perform 
calibration (correction) using the correction data detecting unit 109, the 
third memory 110, and the correcting unit 111 shown in FIG. 1. 
The above description is based on the assumption that an arrangement for 
detecting a mean value is employed, as the power detector 12. However, in 
particular, when a peak power need be detected in the measurement of the 
spectrum of a modulated pulse, a diode element 12a for detecting an input 
signal from the signal branching circuit 11 or the signal switching 
circuit 11a, and a peak hold circuit 12b for holding a peak value of the 
detected output of the diode element 12a may be arranged as the power 
detector 12, as shown in FIG. 7. The peak hold circuit 12b receives a 
reset signal from the data processing and control section 8' upon every 
measuring periods. Note that a mean value circuit 12c is arranged in the 
power detector 12 shown in FIG. 7 to obtain a mean value of the detected 
outputs from the diode element 12a. In addition, the power detector 12 
includes a switch 12d for switching outputs from the mean value circuit 
12c and the peak hold circuit 12b in accordance with applications. 
FIG. 8 shows an example of display of the spectrum distribution data D2 and 
the peak value P2 of a modulated pulse. 
FIG. 9 shows a block arrangement applied to an optical spectrum analyzer, 
as a fourth embodiment. The same reference numerals in FIG. 9 denote the 
same parts as in FIG. 2, and a description thereof is omitted. More 
specifically, an optical signal to be measured a' input to an optical 
signal input terminal 9' is branched into two signals by an optical signal 
branching section 11' including, e.g., a half mirror. One optical signal 
is input to a half mirror 1a' of an RF section 1'. The half mirror 1a' 
receives an optical local oscillation signal from an electrooptical 
converter 1b' of, e.g., a light-emitting diode in response to an optical 
sweep signal from a sweep signal generating section 7. Therefore, the half 
mirror 1a' performs a mixer operation equal to that of an electrical mixer 
to output an optical intermediate-frequency signal. The optical 
intermediate-frequency signal is converted into an electrical 
intermediate-frequency signal by a photoelectric converter 1c such as a 
photodiode. Therefore, the following steps are the same as those in FIG. 
2. 
The other optical signal from the optical signal branching section 11' is 
photoelectrically converted by an optical power sensor 12' including a 
light-receiving element such as a photodiode. At the same time, the 
optical power of the optical signal is detected. Therefore, the following 
steps are the same as those in FIG. 2 except that an optical power value 
signal g in FIG. 9 replaces the power value signal g in FIG. 2. 
According to the fourth embodiment, therefore, the optical spectrum 
distribution data and the optical power value are displayed on a single 
screen in the same manner as in FIGS. 4 and 8. 
In FIGS. 5 to 7, an application to the optical spectrum analyzer can be 
performed in the same manner as in the fourth embodiment in FIG. 9. 
Note that reference numeral 1d in FIG. 9 denotes a programmable optical 
attenuator controlled by a data processing and control section 8. The 
optical attenuator 1d suppresses an excessive input level to be a proper 
level in the same manner as in the variable attenuator 114 in FIG. 1. 
As has been described above, according to the present invention, a signal 
to be measured is distributed to a signal processing section and a power 
detector through a signal branching section. Therefore, there is provided 
a spectrum analyzer which can easily and accurately display normal 
spectrum distribution data together with a power value, and can be applied 
to a wide range of signals including an electrical signal and an optical 
signal.