Amplitude shift keyed receiver

An amplitude shift keyed (ASK) receiver includes a signal receiving part receiving an amplitude shift keyed signal, a signal detecting part coupled to the signal receiving part and detecting a signal having a carrier frequency and a noise, a pulse detecting part coupled to the signal receiving part and checking the signal from the signal receiving part for compensating errors in the signal detecting part, and a signal determining part coupled to the signal detecting part and the pulse detecting part, the signal determining part determining and restoring a signal to be restored according to output signals from the signal detecting part and the pulse detecting part.

This application claims the benefit of Korean Patent Application No. 
45052/1996 filed Oct. 10, 1996, which is hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an ASK(Amplitude Shift Keyed) receiver, 
and more particularly, to an ASK receiver using a digital circuit. 
2. Discussion of the Related Art 
An ASK technique is a modulation technique used in communication 
technology. For digital signals such as `0` and `1`, one signal is carried 
with a frequency and the other is carried without a frequency as shown in 
FIG. 1. A conventional ASK receiver will be explained with reference to 
FIG. 2. 
As shown in FIG. 2, a conventional ASK receiver includes a pre-amplifying 
part 1 for amplifying an amplitude shift keyed and received signal, a band 
pass filter 2 for passing a signal only within a predetermined band of the 
signals from the pre-amplifying part 1, a detector 3 for obtaining an 
original low frequency signal from an output of the band pass filter 2, a 
delaying part 4 for delaying a signal from the detector 3 for a 
predetermined period of time, a signal stretcher 5 for stretching a signal 
from the detector 3 using a capacitor, a dynamic threshold generator 6 for 
generating a threshold value for determining whether the received signal 
exceeds a noise level, and a microprocessor 7. 
The operation of the conventional ASK receiver having the aforementioned 
system will now be explained. Referring to FIG. 2, in order to obtain a 
signal only within a predetermined band, an amplitude shift keyed and 
received signal is amplified through the pre-amplifying part 1 and 
filtered by the band pass filter 2. The filtered signal is received at the 
detector 3. The detector 3 generates a high bit level pulse if a carrier 
signal is present and produces a low bit level pulse if no carrier signal 
is detected. Then, the output signal from the above detector 3 is inputted 
to the delaying part 4, the signal stretcher 5, and the dynamic threshold 
generator 6, respectively. The delaying part 4 delays the signal generated 
from the detector 3 for a predetermined period of time, and the signal 
stretcher 5 stretches the signal using a capacitor. The dynamic threshold 
generator 6 produces a threshold value for determining whether a received 
signal exceeds a noise level. Those signals from the detector 3 delayed 
for a predetermined period of time by the delaying part 4 that are greater 
than the threshold value generated from the threshold generator 6 and at 
the same time have a section greater than the signal stretched in the 
signal stretcher 5 are produced as a high bit digital signal. The signals 
in the remaining sections are produced as low bit digital signals. 
Finally, the outputted values are transmitted to the microprocessor 7 and 
converted to binary digit signals. 
However, the conventional ASK receiver has the following problems. First, 
the conventional ASK receiver uses an analog signal system which has low 
reliability and high power consumption. Second, realization of a highly 
integrated device with other digital circuits is difficult, and a separate 
analog power source generates high noise level. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed to an amplitude shift keyed 
receiver that substantially obviates one or more of the problems due to 
limitations and disadvantages of the related art. 
An object of the present invention is to provide an amplitude shift keyed 
receiver with high reliability and lower power consumption. 
Additional features and advantages of the invention will be set forth in 
the description which follows, and in part will be from the description, 
or may be learned by practice of the invention. The objectives and other 
advantages of the invention will be realized and attained by the structure 
particularly pointed out in the written description and claims hereof as 
well as the appended drawings. 
To achieve these and other advantages and in accordance with the purpose of 
the present invention, as embodied and broadly described, the amplitude 
shift keyed receiver using an infrared ray used therein includes a signal 
receiving part receiving an amplitude shift keyed signal, a signal 
detecting part coupled to the signal receiving part and detecting a signal 
having a carrier frequency and a noise, a pulse detecting part coupled to 
the signal receiving part and checking a signal from the signal receiving 
part for compensating errors in the signal detecting part, and a signal 
determining part coupled to the signal detecting part and the pulse 
detecting part and determining and restoring a signal to be restored 
according to output signals from the signal detecting part and the pulse 
detecting part. 
In another aspect of the present invention, the receiver includes a 
pre-amplifying part amplifying a received amplitude shift keyed signal to 
a predetermined amplitude, a quantizing part coupled to the pre-amplifying 
part and amplifying a signal from the pre-amplifying part and digitizing 
the signal, an ASK edge counting part coupled to the quantizing part and 
determining a presence of carrier frequency in a signal from the 
quantizing part, an oscillating part coupled to the ASK edge counting part 
and generating a clock signal at predetermined intervals and informing the 
ASK edge counting part to start count edges of the amplitude shift keyed 
signal, a comparing part coupled to the ASK edge counting part and 
comparing an output from the ASK edge counting part with a predetermined 
reference value, a pulse detecting part coupled to the signal receiving 
part and checking a signal from the signal receiving part for compensating 
errors in the oscillating part, the ASK edge counting part, and the 
comparing part, a counter and random part coupled to the comparing part 
and the pulse detecting part and combining signals from the ASK edge 
counting part and the pulse detecting part to restore a signal, and a 
hexadecimal counting part coupled to the counter and random part and a 
clock signal and receiving signals from the counter and random part and 
the clock signal and restoring the signal to original signal. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary explanatory and are intended 
to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made in detail to the preferred embodiments of the 
present invention, examples of which are illustrated in the accompanying 
drawings. 
FIG. 3 is an example of a device suitable for short distance radio 
communications such as communications between personal computers or 
personal computer to printer. 
As shown in FIG. 3, the amplitude shift keyed receiver of the present 
invention includes a signal receiving part 21 for receiving an amplitude 
shift keyed (ASK) signal. A signal detecting part 22 detects a signal 
having a carrier frequency (or signal having no carrier frequency) from 
the received ASK signal and also detects noise. A pulse detecting part 23 
checks a signal from the signal receiving part 21 by a predetermined unit 
for compensating errors in the signal detecting part 22. A signal 
determining part 24 determines and restores a signal to be restored 
according to output signals from the signal detecting part 22 and the 
pulse detecting part 23. 
The signal receiving part 21 has a pre-amplifying part 21a and a quantizing 
(or digitizing) part 21b. After amplifying the amplitude shift keyed input 
signal to a predetermined amplitude in the pre-amplifying part 21a, the 
signal receiving part 21 digitizes the amplified signal in the quantizing 
part 21b. The signal receiving part 21 produces a signal having an 
amplitude shift keyed carrier frequency corresponding to a binary digit. 
On the other hand, the signal receiving part 21 outputs a signal without a 
carrier frequency (low bit data) for the remaining binary digits. 
The signal detecting part 22 includes an oscillating part 22a, an ASK edge 
counting part 22b, and a comparing part 22c. The oscillating part 22a 
generates a clock signal for a predetermined cycle (for example, a 
counting cycle of 13 .mu.s) informing the ASK edge counting part 22b to 
start counting. For example, the oscillating part 22a generates a 1 .mu.s 
pulse during a 13 .mu.s cycle. That is, pulses having `0` during 12 .mu.s 
and having `1` during 1 .mu.s are generated. The pulses are generated by, 
for example, 13 counters receiving a 1 MHZ clock signal. The ASK edge 
counting part 22b counts up the edges of the amplitude shift keyed and 
received signal according to the clock signal for a predetermined cycle 
received from the oscillating part 22a. The clock signal of a 
predetermined cycle informing the ASK edge counting part 22b to start 
counting generated in the oscillating part 22a is produced at 
predetermined intervals irrespective of bit time. 
Accordingly, the ASK edge counting part 22b determines a presence of the 
carrier frequency every 13 .mu.s, for example. In other words, the ASK 
edge counting part 22b counts a pulse edge for 12 .mu.s during the 13 
.mu.s cycle. The ASK edge counting part 22b is cleared during the 
remaining 1 .mu.s, and the counted value is applied to the comparing part 
22c. The comparing part 22c compares the counted value from the ASK edge 
counting part 22b with a predetermined reference value. As an example, for 
a received ASK carrier frequency of 500 KHz, the comparing part 22c uses a 
predetermined reference value of 6. For example, if data in a high section 
of the pulse in the quantized signal is "1" and the other section is "0", 
the ASK counting part 22c counts a number of pulse edges in the high 
section. 
In an IR(Infrared) communication, in general, a signal oscillation of 500 
KHz is made for data of "1" and a low bit data is outputted for data of 
"0". For data of "1," a count is performed 6 times during 13 .mu.s. For 
example, when a transmission rate is as low as 2400 bps, a cycle of one 
bit time is 417 .mu.s. Since the signal has a frequency of 500 KHz, 
approximately 208 pulses are present in one bit time. The comparing part 
22c determines within .+-.20% error whether the signal has a carrier 
signal by comparing a received counted value to a reference value. The 
comparing part 22c determines that the signal has a carrier signal if the 
counted value from the ASK edge counting part 22b falls in a range of "4" 
to "8" which is a value after considering the .+-.20k error on 6 pulses. 
If the counted value is not within the range, the comparing part 22c 
determines that the signal has no carrier signal. 
The pulse detecting part 23 generates a signal for compensating errors of 
the signal detecting part 22 and includes a counter and a control logic. 
As explained above, for the normal ASK signal without any noise, the 
signal oscillates with a frequency of 500 KHz for "1" data. However, even 
for cases where it is certain that the data is "1," if the signal has a 
weak noise in any of the section oscillating with the 500 KHz frequency, a 
pulse width oscillating with the 500 KHz in a portion having the noise 
becomes longer. If this happens, the counted value of the pulse edge 
portions in predetermined intervals in the ASK edge counting part 22b does 
not satisfy the predetermined range of 4 to 8. Accordingly, even though it 
is "1" data, the "1" data is not detected as "1" data. However, the pulse 
detecting part 23 compensate for such an error. Then, the signal 
determining part 24 receives output signals from the comparing part 22c 
and the pulse detecting part 23. 
The signal determining part 24 includes a counter and random part 24a and a 
hexadecimal counting part 24b. The counter and random part 24a and a 
hexadecimal counting part 24b receive the outputs from the pulse detecting 
part 23 and the comparing part 22c and remove the possibility of signal 
distortion from noises. Specifically, the counter and random part 24a 
combines the signals from the ASK edge counting part and the pulse 
detecting part to restore a signal. In addition, the counter and random 
part 24a transmits a binary digit corresponding to one bit time to the 
hexadecimal counting part 24 at a transmission rate (for example, 2400, 
4800, or 9600 bps) using a clock signal having a speed 16 times the signal 
transmission rate. 
The operation of the ASK receiver in accordance with a preferred embodiment 
of the present invention will now be explained. 
Referring to FIG. 3, an amplitude shift keyed signal received externally 
from the ASK receiver is amplified to a predetermined amplitude in the 
pre-amplification part 21a and quantized in the quantizing part 21b. The 
quantized signal includes a signal having an ASK carrier frequency 
corresponding to one binary digit and signals having no carrier frequency 
for the remaining binary digits. The output from the signal receiving part 
21 is sent to the signal detecting part 22 including the ASK edge counting 
part 22b and to the pulse detecting part 23. The ASK edge counting part 
22b counts edge portions of signals that is outputted from the signal 
receiving part 21 in every 13 .mu.s intervals generated in the oscillating 
part 22a. Counting the edge portions determines whether the transmitted 
signal has a carrier frequency. When a next oscillation frequency is 
generated, the ASK counting part 22b is cleared, and the counted value is 
transmitted to the comparing part 22c. 
The comparing part 22c determines whether the signal has a carrier 
frequency by comparing the counted value received from the ASK edge 
counting part 22b with a reference value. In other words, the comparing 
part 22c confirms that a signal has a carrier frequency if the counted 
value falls in a range of 4 to 8, for example, where the reference value 
is 6. Conversely, it is determined that the signal has no carrier 
frequency if the counted value is not in the range. The pulse detecting 
part 23 generates a signal when a data exists in the signal outputted from 
the signal receiving part 21. The signal generated considers the signal 
from the signal receiving part 21 as a normal signal even if the signal 
partly has a weak noise. 
Outputs from the pulse detecting part 23 and the comparing part 22c are 
transmitted to the signal determining part 24. The counter and random part 
24a in the signal determining part 24 outputs the signals in the sections 
where the signals outputted from the pulse detecting part 23 and the 
comparing part 22c are identical while using a clock signal having a speed 
16 times the signal transmission rate. The hexadecimal counting part 24b 
receives a signal from the counter and random part 24a and restores the 
signal to the original signal. 
FIGS. 4A-4F illustrate signal timings in the amplitude shift keyed receiver 
of the present invention. 
FIG. 4A represents a signal from the signal receiving part 21 which 
oscillates with 500 KHz frequency if the signal data is "1" and maintains 
a low signal if the signal data is "0". FIG. 4B represents a signal from 
the oscillating part 22a having pulse duration of 13 .mu.s, for example. 
These pulses act as a clock signal to count oscillating pulse edge 
portions in the output signal from the signal receiving part 21. FIG. 4C 
represents a pulse waveform from the comparing part 22c showing a result 
of the counted oscillating pulse edge portion of an output signal from the 
signal receiving part 21 executed by the ASK edge counting part 22b under 
the control of the oscillating part 22a. That is, if the result of edge 
portion counting of the pulses for 13 .mu.s falls in the range of 4 to 8, 
where the reference value is 6, the pulse changes to a low level. 
FIG. 4D represents a waveform from the pulse detecting part 23. The signal 
is changed to a low level when the outputted signal from the signal 
receiving part 21 starts to oscillate. In this process, the signal shown 
in FIG. 4D should be changed to a high level again if the signal from the 
signal receiving part 21 does not oscillate. The signal is maintained as 
the low level for a predetermined period of time to compensate for the 
possible error which can occur when the oscillating pulses of the signal 
from the signal receiving part 21 contain weak noises. 
FIG. 4E represents a waveform from the counter and random part 24a. The 
signal is a waveform selectively taken from portions of the waveforms from 
the comparing part 22c (FIG. 4C) and the pulse detecting part 23 (FIG. 4D) 
that satisfies the two waveforms simultaneously. The waveform from the 
counter and random part 24a is restored into an original signal for one 
bit time, as shown in FIG. 4F, by the hexadecimal counting part 24b. 
Accordingly, the ASK receiver of the present invention has the following 
advantages. First, the ASK receiver using a digital circuit improves its 
reliability. Second, integration of the receiver with other digital 
circuits is easy. Third, an ASK receiver having a lower noise can be 
designed using a low power consumption source. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the amplitude shift keyed receiver of the 
present invention without departing from the spirit or scope of the 
invention. Thus, it is intended that the present invention cover the 
modifications and variations of this invention provided they come within 
the scope of the appended claims and their equivalents.