Comparator device for selecting received signals

A comparator device is designed for comparing the signal levels of first and second input signals to provide respective resultant comparator outputs independently, which comparator device is featured in avoidance of occurrence of simultaneous low levels of the comparator signals at all possible conditions of the comparator outputs. The comparator device includes first and second comparator which independently output resultant comparator outputs having either a high (H) level or a low (L) level as results of comparison of the signal levels of the first and second input signals while taking one of the input signals as a reference, and have offset characteristics and hysteresis characteristics so that the comparator outputs, either H level or L level, can be fixedly determined when the first and second input signal levels are equal to each other. The first input signal is applied to one of the input terminal of the first comparator and the other input terminal of the second comparator with a different polarity, and the second input signal is applied to the other input terminal of the first comparator and one of the input terminal of the second comparator with a different polarity.

BACKGROUND OF THE INVENTION 
The present invention relates to a comparator device applicable for 
switching control for a plurality of paths in a multi-path transmission 
system receiving an identical modulation signal through a plurality of 
receiving sections, such as a diversity reception system. 
In general, a comparator device to be applied for such type of a diversity 
reception system includes first and second comparator means having 
identical hysteresis characteristics. With these comparator means, 
voltages corresponding to receiving conditions at two transmission paths 
are compared to control transmission means for transmitting a transmitting 
signal based on respective comparator outputs. Control is typically 
performed to switch one of the comparator means from a conducting state to 
a non-conducting state and the other comparator means from a 
non-conducting state to a conducting state. Upon input, both of the 
transmission means for the transmitting signal temporarily become 
conductive for avoiding drop out of the transmitting signal or click noise 
due to delay in response at the transmission means. 
Here, a diversity receiver having typical two receiving sections, for which 
the conventional comparator device is applied, is schematically 
illustrated in FIG. 1. 
In the diversity receiver illustrated in FIG. 1, the reference numerals 1 
and 2 denote first and second antennas corresponding to respective 
receiving channels for receiving a common modulation signal, 10 and 20 
denote first and second receiver means respectively corresponding to the 
receiving channels. Through respective receiving channels, first and 
second demodulation signal outputs of the received signals, and first and 
second receiving condition signals V.sub.1 and V.sub.2 corresponding to 
the receiving conditions of respective receiving channels are obtained. 
The first and second receiving condition signals V.sub.1 and V.sub.2 have 
characteristics to be greater for better receiving condition. 
The reference numerals 11 and 21 denote first and second variable 
transmission means for transmitting the first and second demodulated 
signals from the first and second receiving means 10 and 20 to a common 
output terminal 14. 
The reference numerals 12 and 22 denote first and second comparator means 
which have identical hysteresis characteristics. Respective pairs of 
inputs of the first and second comparator means 12 and 22 have mutually 
different polarities and the inputs having the different polarities are 
connected to each other. The first and second receiving condition signals 
V.sub.1 and V.sub.2 are supplied from the first and second receiver means 
10 and 20 to respective inputs of the first and second comparator means 12 
and 22. The first and second comparator means 12 and 22 compare the inputs 
and respectively output first and second comparator output condition 
signals S.sub.1 and S.sub.2. The outputs of the first and second 
comparator means 12 and 22 are respectively supplied to corresponding ones 
of the first and second variable transmission means 11 and 21 so that the 
variable transmission means is controlled into a conducting state in 
response to HIGH level (hereinafter simply referred to as "H") of the 
corresponding ones of the first and second comparator output condition 
signals S.sub.1 and S.sub.2, and into a non-conducting state in response 
to LOW level (hereinafter simply referred to as "L") of the corresponding 
ones of the first and second comparating output condition signals S.sub.1 
and S.sub.2. Therefore, one of the first demodulated signal from the first 
receiver means 10 and the second demodulated signal from the second 
receiver means 20 is selectively transmitted to the output terminal 14. 
Subsequently, the operation of the conventional diversity receiver having 
the construction as set forth above will be discussed with reference to 
FIG. 2. 
FIG. 2 illustrates the relationship between the first and second receiving 
condition signals V.sub.1 and V.sub.2 as the inputs for the first and 
second comparator means 12 and 22 and the first and second comparator 
outputs condition signals S.sub.1 and S.sub.2 as the outputs thereof. 
Here, (a) and (b) of FIG. 2 shows the relationship between the threshold 
values of the first and second comparing means 12 and 22 having identical 
hysteresis characteristics and the comparator outputs condition signals 
S.sub.1 and S.sub.2, with respect to the first receiving condition signal 
V.sub.1. For these first and second comparator means 12 and 22, the same 
threshold values are provided. The threshold values for each of the 
comparator means 12 and 22 are determined such that, taking the 
non-inverting input thereof as a reference value, an average of two 
threshold values of each comparator means, i.e. one half of the sum of the 
threshold values, is greater than the reference value, and the reference 
value is present between two threshold values. Therefore, when the 
inverting inputs have a value equal to the reference value, the comparator 
output condition signal of the comparator means can be either H or L. 
In case that the difference polarities of inputs of the first and second 
comparator means 12 and 22 are connected to the first and second receiver 
means 10 and 20 and taking the first receiving condition signal V.sub.1 as 
a reference, the relationship of the levels of the threshold values in the 
second comparing means 22 is reversed so that the average value of two 
threshold values becomes smaller than the reference value as can be seen 
in (b) of FIG. 2. Therefore, when such connection is established, the 
threshold values of respective ones of the first and second comparing 
means 12 and 22 should have mutually different values to perform the 
operations as illustrated in (a) and (b) of FIG. 2. 
Namely, assuming V.sub.2 &lt;&lt;V.sub.1, S.sub.1 =H and S.sub.2 =L are 
established so that the demodulated signal of the receiver means 10 is 
supplied to the output terminal 14. 
Here, when the level of the second receiving condition signal V.sub.2 rises 
to reach the threshold value across which output of the comparator means 
22 is switched from L to H, S.sub.1 =H and S.sub.2 =H are established so 
that the first demodulated signal of the first receiver means 10 and the 
second demodulated signal of the second receiver means 20 are supplied to 
the output terminal 14 in parallel. At this time, since each of the 
demodulated signals is derived through demodulation of the same modulation 
signals and thus should have the same amplitude, such parallel supply 
condition of the demodulated signals will never cause variation of the 
amplitude. When the level of the second receiving condition signal V.sub.2 
further rises to reach the threshold value, across which the first 
comparator output condition signal of the first comparator means 12 is 
switched from H to L, S.sub.1 =L and S.sub.2 =H are established so that 
the second demodulated signal of the second receiver means 20 is supplied 
to the output terminal 14 and the first demodulated signal of the first 
receiver means 10 is disconnected from the output terminal 14 for 
completing the switching operation. 
In FIG. 2, (c) and (d) show all possible transitions of the first and 
second comparator output condition signals S.sub.1 and S.sub.2 relative to 
variation of the second receiving condition signal V.sub.2 taking the 
first receiving condition signal V.sub.1 as a reference. As can be seen 
therefrom, at the transition according to variation of the first and 
second receiving condition signals V.sub.1 and V.sub.2 for switching 
supply of the demodulated signals from that of the first receiving means 
10 to that of the second receiving means, and vice versa, both of the 
first and second demodulated signals are supplied to the output terminal 
in parallel, temporarily. Since the hysteresis of respective ones of the 
comparator means 12 and 22 will not change even when the amplitude of the 
first receiving condition signal V.sub.1, taken as a reference, changes, 
the condition of the operation is not dependent on the first receiving 
condition signal V.sub.1. 
As set forth above, even in the conventional comparator device, as applied 
to the diversity receiver, both of the demodulated signals are temporarily 
transmitted at the transition for switching demodulated outputs of two 
receiver means for avoiding occurrence of signal drop out in click noise 
due to delay of operation in the transmission means. Also, since it 
utilizes the hysteresis characteristics, the transmission state, in which 
both of the demodulated outputs are transmitted, is past at a speed 
proportional to the speed of variation even at high variation speed of the 
receiving condition signals and thus can follow even for substantial 
variation of the switching frequency. 
However, in the conventional comparator device constructed as set forth 
above, as can be seen in (d) of FIG. 2, a problem is encountered in that 
the condition, in which none of the demodulated signals of the first and 
second receiver means 10 and 20 is transmitted, i.e., the condition where 
both of the comparator output condition signals S.sub.1 and S.sub.2 are L, 
resides in the proximity of the important portion where the receiving 
condition signals V.sub.1 and V.sub.2 are close to each other. Though such 
condition may not be introduced during normal operation, there is a 
possibility of introduction as affected by noise and so forth. This makes 
it difficult to guarantee reception which is the fundamental task of the 
diversity reception system. 
SUMMARY OF THE INVENTION 
The present invention is to solve such problems in the prior art. 
Therefore, it is an object of the present invention to provide a 
comparator device which does not have the condition where both comparator 
outputs become L at any condition of the comparator outputs, can 
temporarily transmit more than one demodulated outputs during transition 
for successfully avoiding signal drop out or click noise due to delay of 
operation of the transmission means, and has a capability of comparing two 
or more signals. 
In order to accomplish above-mentioned objects, a comparator device, 
according to the present invention, is designed for comparing the signal 
levels of first and second input signals to provide respective resultant 
comparator outputs independently. The comparator device includes first and 
second comparator means which independently output resultant comparator 
outputs either of H level and L level as results of comparison of the 
signal levels of the first and second input signals with taking one of the 
input signals as reference, said means having offset characteristics and 
hysteresis characteristics so that the comparator outputs, either H level 
or L level, can be fixedly determined when the first and second input 
signal levels are equal to each other. The first input signal is applied 
to one of the input terminal of the first comparator means and the other 
input terminal of the second comparator means with different polarity, and 
the second input signal is applied to the other input terminals of the 
first comparator means and one of the input terminal of the second 
comparator means, having different polarity. 
Also, the comparator device, according to the present invention, is 
designed for separately comparing signal levels of a plurality of input 
signals, and for outputting resultant comparator outputs. The comparator 
device has a maximum value (minimum value) determining and selecting means 
for determining a maximum value (or minimum value) input signal among the 
input signals. 
The comparator device also has a plurality of comparator means for 
receiving the input signal at one input terminal and signals outputted 
from the maximum value (minimum value) determining and selecting means at 
the other terminals, and separately outputting either H level or L level 
as results of comparison of the signal levels of the input signals, said 
comparator means having offset characteristics and hysteresis 
characteristics so that the comparator outputs being fixedly determined 
when the input terminals levels are equal to each other. 
Accordingly, in the comparator device constructed as set forth above, since 
the first and second comparator means are provided offset characteristics 
and the hysteresis characteristics for fixedly determining the comparator 
output either at H level or L level when the signal levels inputted to the 
input terminals of the comparator means are equal to each other, the 
comparator outputs as the results of comparison will become alternatively 
H level and L level or become both H levels, and cannot become both L 
levels. 
According to a first case, the present claimed invention is directed to 
providing a comparator device for comparing signal levels of first and 
second input signals and outputting independently two comparison results, 
said device comprising: 
first and second comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when the 
level of the signal applied to said second terminal minus the level of the 
signal applied to said first terminal is less than a first predetermined 
level, (b) which has a second value when the level of the signal applied 
to said second terminal minus the level of the signal applied to said 
first terminal is greater than a second predetermined level, said second 
predetermined level being larger than said first predetermined level, (c) 
which, when a difference between the level of the signal applied to said 
second terminal and that applied to said first terminal lies within a 
range between said first predetermined level and said second predetermined 
level, maintains its value at a preceding one of said first and second 
values that it had before said difference entered said range, and (d) 
which takes said first value when the level of the signal applied to said 
first terminal is equal to the level of the signal applied to said second 
terminal; 
means for applying said first input signal to the first terminal of said 
first comparator means and to the second terminal of said second 
comparator means; 
means for applying said second input signal to the second terminal of said 
first comparator means and to the first terminal of said second comparator 
means; and 
means for outputting the binary signals output from said first and second 
comparator means as the two comparison result of said comparator device. 
According to a second case, the present invention is directed to providing 
a comparator device for comparing signal levels of first and second input 
signals and outputting independently two comparison results, said device 
comprising: 
first and second comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when the 
level of the signal applied to said first terminal minus the level of the 
signal applied to said second terminal is greater than a first 
predetermined level, (b) which has a second value when the level of the 
signal applied to said first terminal minus the level of the signal 
applied to said second terminal is less than a second predetermined level, 
said second predetermined level being less than said first predetermined 
level, (c) which, when a difference between the level of the signal 
applied to said first terminal and that applied to said second terminal 
lies within a range between said first predetermined level and said second 
predetermined level, maintains its value at a preceding one of said first 
and second values that it had before said difference entered said range, 
and (d) which takes said second value when the level of the signal applied 
to said first terminal is equal to the level of the signal applied to said 
second terminal; 
means for applying said first input signal to the first terminal of said 
first comparator means and to the second terminal of said second 
comparator means; 
means for applying said second input signal to the second terminal of said 
first comparator means and to the first terminal of said second comparator 
means; and 
means for outputting the binary signals output from said first and second 
comparator means as the two comparison results of said comparator device. 
According to a third case, the present invention is directed to providing a 
comparator device for comparing signal levels of first and second input 
signals and outputting independently two comparison results, said device 
comprising: 
first and second comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when a 
ratio of the level of the signal applied to said first terminal to the 
level of the signal applied to said second terminal is greater than a 
first predetermined ratio, (b) which has a second value when the ratio of 
the level of the signal applied to said first terminal to the level of the 
signal applied to said second terminal is less than a second predetermined 
ratio, said first predetermined ratio being larger than said second 
predetermined ratio and less than 1, (c) which, when the ratio of the 
level of the signal applied to the first terminal to the level of the 
signal applied to the second terminal lies within a range between said 
first predetermined ratio and said second predetermined ratio, maintains 
its value at a preceding one of said first and second values that it had 
before said ratio entered said range, and (d) which takes said first value 
when the level of the signal applied to said first terminal is equal to 
the level of the signal applied to said second terminal; 
means for applying said first input signal to the first terminal of said 
first comparator means and to the second terminal of said second 
comparator means: 
means for applying said second input signal to the second terminal of said 
first comparator means and to the first terminal of said second comparator 
means; and 
means for outputting the binary signals output from said first and second 
comparator means as the two comparison results of said comparator device. 
According to a fourth case, the present invention is directed to providing 
a comparator device for comparing signal levels of first and second input 
signals and outputting independently two comparison results, said device 
comprising: 
first and second comparator means, each including a first terminal and 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when a 
ratio of the level of the signal applied to said first terminal to the 
level of the signal applied to said second terminal is greater than a 
first predetermined ratio, (b) which has a second value when the ratio of 
the level of the signal applied to said first terminal to the level of the 
signal applied to said second terminal is less than a second predetermined 
ratio, said second predetermined ratio being larger than 1 and less than 
said first predetermined ratio, (c) which, when the ratio of the level of 
the first terminal signal to the level of the second terminal signal lies 
within a range between said first predetermined level and said second 
predetermined level, maintains its value at a preceding one of said first 
and second values that it had before said ratio entered said range, and 
(d) which takes said second value when the level of the signal applied to 
said first terminal is equal to the level of the signal applied to said 
second terminal; 
means for applying said first input signal to the first terminal of said 
first comparator means and to the second terminal of said second 
comparator means; 
means for applying said second input signal to the second terminal of said 
first comparator means and to the first terminal of said second comparator 
means; and 
means for outputting the binary signals output from said first and second 
comparator means as the two comparison results of said comparator device. 
According to a fifth case, the present invention is directed to providing a 
comparator device for comparing signal levels of a plurality of input 
signals and outputting independently comparison results for each input 
signal, said device comprising: 
maximum level determining means for determining an input signal having a 
maximum level among said plurality of input signals and outputting a 
signal corresponding to the determined maximum level input signal; 
a plurality of comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when the 
level of the signal applied to said second terminal minus the level of the 
signal applied to said first terminal is less than a first predetermined 
level, (b) which has a second value when the level of the signal applied 
to said second terminal minus the level of the signal applied to said 
first terminal is greater than a second predetermined level, said second 
predetermined level being larger than said first predetermined level, (c) 
which, when a difference between the level of the signal applied to said 
second terminal and that applied to said first terminal lies within a 
range between said first predetermined level and said second predetermined 
level, maintains its value at a preceding one of said first and second 
values that it had before said difference entered said range, and (d) 
which takes said first value when the level of the signal applied to said 
first terminal is equal to the level of the signal applied to said second 
terminal; 
means for applying said input signals to the first terminals of said 
comparator means respectively; 
means for applying the signal output from said maximum level determining 
means to the second terminal of each comparator means; and 
means for outputting the binary signals output from said comparator means 
as the comparison results of said comparator device. 
According to a sixth case, the present invention is directed to providing a 
comparator device for comparing signal levels of a plurality of input 
signals and outputting independently comparison results for each input 
signal, said device comprising: 
minimum level determining means for determining an input signal having a 
minimum level among said plurality of input signals and outputting a 
signal corresponding to the determined minimum level input signal; 
a plurality of comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when the 
level of the signal applied to said first terminal minus the level of the 
signal applied to said second terminal is greater than a first 
predetermined level, (b) which has a second value when the level of the 
signal applied to said first terminal minus the level of the signal 
applied to said second terminal is less than a second predetermined level, 
said second predetermined level being less than said first predetermined 
level, which, when a difference between the level of the signal applied to 
said first terminal and that applied to said second terminal lies within a 
range between said first predetermined level and said second predetermined 
level, maintains its value at the preceding one of said first and second 
values that it had before said difference entered said range, and (d) 
which takes said second value when the level of the signal applied to said 
first terminal is equal to the level of the signal applied to said second 
terminal; 
means for applying said input signals to the first terminals of said 
comparator means respectively; 
means for applying the signal output from said minimum level determining 
means to the second terminal of each comparator means; and 
means for outputting the binary signals output from said comparator means 
as the comparison results of said comparator device. 
According to a seventh case, the present invention is directed to providing 
a comparator device for comparing signal levels of a plurality of input 
signals and outputting independently comparison results for each input 
signal, said device comprising: 
maximum level determining means for determining an input signal having a 
maximum level among said plurality of input signals and outputting a 
signal corresponding to the determined maximum level input signal; 
a plurality of comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when a 
ratio of the level of the signal applied to said first terminal to the 
level of the signal applied to said second terminal is greater than a 
first predetermined ratio, (b) which has a second value when the ratio of 
the level of the signal applied to said first terminal to the level of the 
signal applied to said second terminal is less than a second predetermined 
ratio, said first predetermined ratio being larger than said second 
predetermined ratio and less than 1, (c) which, when the ratio of the 
level of the signal applied to the first terminal to the level of the 
signal applied to the second terminal lies within a range between said 
first predetermined ratio and said second predetermined ratio, maintains 
its value at a preceding one of said first and second values that it had 
before said ratio entered said range, and (d) which takes said first value 
when the level of the signal applied to said first terminal is equal to 
the level of the signal applied to said second terminal; 
means for applying said input signals to the first terminals of said 
comparator means respectively; 
means for applying the signal output from said maximum level determining 
means to the second terminal of each comparator means; 
means for outputting the binary signals output from said comparator means 
as the comparison results of said comparator device. 
According to an eighth case, the present invention is directed to providing 
a comparator device for comparing signal levels of a plurality of input 
signals and outputting independently comparison results for each input 
signal, said device comprising: 
minimum level determining means for determining an input signal having a 
minimum level among said plurality of input signals and outputting a 
signal corresponding to the determined minimum level input signal; 
a plurality of comparator means, each including a first terminal and a 
second terminal and each for comparing a level of a signal applied to said 
first terminal with a level of a signal applied to said second terminal 
and for outputting a binary signal (a) which has a first value when a 
ratio of the level of the signal applied to said first terminal to the 
level of the signal applied to said second terminal is greater than a 
first predetermined ratio, (b) which has a second value when the ratio of 
the level of the signal applied to said first terminal to the level of the 
signal applied to said second terminal is less than a second predetermined 
ratio, said second predetermined ratio being larger than 1 and less than 
said first predetermined ratio, (c) which, when the ratio of the level of 
the first terminal signal to the level of the second terminal signal lies 
within a range between said first predetermined level and said second 
predetermined level, maintains its value at a preceding one of said first 
and second values that it had before said ratio entered said range, and 
(d) which takes said second value when the level of the signal applied to 
said first terminal is equal to the level of the signal applied to said 
second terminal; 
means for applying said input signals to the first terminals of said 
comparator means respectively; 
means for applying the signal output from said minimum level determining 
means to the second terminal of each comparator means; and 
means for outputting the binary signals output from said comparator means 
as the comparison results of said comparator device. 
Another aspect of the present invention is to provide a comparator device 
according to any of the above cases wherein each of said first and second 
comparator means is formed into an integrated module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Various embodiments of comparator devices according to the present 
invention will be discussed herebelow with reference to FIGS. 3 to 7. 
FIG. 3 is a schematic block diagram of a typical diversity receiver to 
which the first embodiment of the comparator device according to the 
present invention is applied. In the construction of the first embodiment 
illustrated in FIG. 3, the elements common to or equivalent to those in 
the conventional construction of FIG. 1 will be represented by the same 
reference numerals. 
In the diversity receiver illustrated in FIG. 3, in which the first 
embodiment of the comparator device is employed, the reference numerals 1 
and 2 denote the first and second antennas corresponding to respective 
receiving channels for receiving a common modulation signal, and 10 and 20 
denote the first and second receiver means respectively corresponding to 
the receiving channels. Through respective receiving channels, first and 
second demodulation signal outputs of the received signals, and the first 
and second receiving condition signals V.sub.1 and V.sub.2 corresponding 
to the receiving conditions of respective receiving channels, are 
obtained. The first and second receiving condition signals V.sub.1 and 
V.sub.2 have characteristics to be greater for better receiving condition. 
The reference numerals 11 and 21 denote the first and second variable 
transmission means for transmitting the first and second demodulated 
signals from the first and second receiving means 10 and 20 to the common 
output terminal 14. 
The reference numerals 112 and 122 denote first and second voltage 
comparison type comparator means respectively including voltage sources 13 
and 23 and comparators 12 and 22. The first and second comparator means 
have identical offset characteristics and hysteresis characteristics. 
Respective pairs of inputs of the first and second comparator 12 and 22 
have mutually different polarities and the inputs having the different 
polarities are connected to each other. The first and second receiving 
condition signals V.sub.1 and V.sub.2 are supplied from the first and 
second receiver means 10 and 20 to respective inputs of the first and 
second comparator means 112 and 122. The first and second comparator means 
112 and 122 compare the inputs and respectively output first and second 
comparator output condition signals S.sub.1 and S.sub.2. The outputs of 
the first and second comparator means 112 and 122 are respectively 
supplied to corresponding ones of the first and second variable 
transmission means 11 and 21 so that the variable transmission means is 
controlled into a conducting state in response to HIGH level of the 
corresponding ones of the first and second comparator output condition 
signals S.sub.1 and S.sub.2, and into a non-conducting state in response 
to LOW level of the corresponding ones of the first and second comparator 
output condition signals S.sub.1 and S.sub.2. Therefore, one of the first 
demodulated signal from the first receiver means 10 and the second 
demodulated signal from the second receiver means 20 is selectively 
transmitted to the output terminal 14. 
Subsequently, the operation of the diversity receiver having the first 
embodiment of the comparator device will be discussed with reference to 
FIG. 4. 
FIG. 4 illustrates the relationship between the first and second receiving 
condition signals V.sub.1 and V.sub.2 as the inputs for the first and 
second comparator means 112 and 122 and the first and second comparator 
outputs condition signals S.sub.1 and S.sub.2 as the outputs thereof. 
Here, (a) and (b) of FIG. 4 show the relationship between the threshold 
values of the first and second comparator means 112 and 122 having 
identical offset characteristics and hysteresis characteristics and the 
comparator outputs condition signals S.sub.1 and S.sub.2, with respect to 
the first receiving condition signal V.sub.1. For these first and second 
comparator means 112 and 122, the same threshold values are provided. The 
threshold values for each of the comparator means 112 and 122 are provided 
offset characteristics so that, taking the non-inverting input thereof as 
a reference value, both of the threshold values are greater than the 
reference value. Since the different polarities of inputs of the first and 
second comparator means 112 and 122 are connected to each other, the 
relationship of the levels of the threshold values in the second comparing 
means 122 is reversed with taking the first receiving condition signal 
V.sub.1 as a reference. Therefore, the operation as illustrated in (b) of 
FIG. 4 can be performed. 
Namely, in a manner identical to the foregoing conventional comparator 
device, assuming V.sub.2 &lt;&lt;V.sub.1, S.sub.1 =H and S.sub.2 =L are 
established so that the demodulated signal of the receiver means 10 is 
supplied to the output terminal 14. Here, when the level of the second 
receiving condition signal V.sub.2 rises to reach the threshold value 
across which output of the comparator means 122 is switched from L to H, 
S.sub.1 =H and S.sub.2 =H are established so that the first demodulated 
signal of the first receiver means 10 and the second demodulated signal of 
the second receiver means 20 are supplied to the output terminal 14 in 
parallel. At this time, since each of the demodulated signals is derived 
through demodulation of the same modulation signals and thus should have 
the same amplitude, such parallel supply condition of the demodulated 
signals will never cause variation of the amplitude. When the level of the 
second receiving condition signal V.sub.2 further rises to reach the 
threshold value, across which the first comparator output condition signal 
of the first comparator means 112 is switched from H to L, S.sub.1 =L and 
S.sub.2 =H are established so that the second demodulated signal of the 
second receiver means 20 is supplied to the output terminal 14 and the 
first demodulated signal of the first receiver means 10 is disconnected 
from the output terminal 14 for completing switching operation. 
In FIG. 4, (c) shows all possible transitions of the first and second 
comparator output condition signals S.sub.1 and S.sub.2 relative to 
variation of the second receiving condition signal V.sub.2 taking the 
first receiving condition signal V.sub.1 as a reference. As apparent from 
(c) of FIG. 4, in the signal level range close to the condition where the 
first and second receiving condition signals V.sub.1 and V.sub.2 become 
equal to each other, the comparator outputs S.sub.1 and S.sub.2 of the 
first and second comparator means 112 and 122 are maintained S.sub.1 =H 
and S.sub.2 =H, and in all possible combinations of the signal levels of 
the first and second receiving condition signal V.sub.1 and V.sub.2, the 
condition in which the first and second comparator outputs become S.sub.1 
=L and S.sub.2 =L will never occur. 
As set forth above, according to the foregoing first embodiment, since the 
comparator device comprises the first and second comparator means which 
have identical offset characteristics and hysteresis characteristics so 
that, when one of the input signals (first input signal in the shown case) 
is taken as a reference, both of the threshold values for the other input 
signal (second input signal in the shown case) become greater than the 
reference value, there is no possibility of occurrence that both of the 
first and second variable transmission means are placed in a 
non-conducting state simultaneously at any combination of two input 
signals. Also, at the transition for switching, two demodulated outputs 
can be temporarily transmitted simultaneously so that the signal drop out 
and click noise due to delay of operation of the transmission means can be 
effectively eliminated. 
FIG. 5 is a schematic block diagram of a diversity receiver having a 
plurality of receiver means, to which the second embodiment of the 
comparator device, according to the present invention, is applied. 
In the diversity receiver of FIG. 5 employing the second embodiment of the 
comparator device, the reference numerals 1, 2, 3 and 4 denote first, 
second, third and fourth antennas corresponding to respective receiving 
channels for respectively receiving a common modulation signal, and 10, 
20, 30 and 40 denote first, second, third and fourth receiver means 
corresponding to the respective receiving channels. The first, second, 
third and fourth receiver means 10, 20, 30 and 40 provide first, second, 
third and fourth demodulated signals and first, second, third and fourth 
receiving condition signals corresponding to respective ones of the 
receiving conditions of the corresponding receiver means. The signal level 
of the first, second, third and fourth receiving condition signals is 
increased at better receiving conditions. 
The reference numerals 11, 21, 31 and 41 denote the first, second, third 
and fourth variable transmission means for transmitting the first, second, 
third and fourth demodulated signals from the first, second, third and 
fourth receiving means 10, 20, 30 and 40 to the common output terminal 14. 
The reference numerals 112, 122, 132 and 142 denote first, second, third 
and fourth voltage comparison type comparator means respectively including 
voltage source 13, 23, 33 and 43 and comparators 12, 22, 32 and 42. The 
first, second, third and fourth comparator means have identical offset 
characteristics and hysteresis characteristics. Respective pairs of inputs 
of the first, second, third and fourth comparators 12, 22, 32 and 42 have 
mutually different polarities and connected to ones of first, second, 
third and fourth receiver means 10, 20, 30 and 40. The respective 
receiving condition signals are supplied from the receiver means 10, 20, 
30 and 40 to respective non-inverting inputs of the first, second, third 
and fourth comparator means 112, 122, 132 and 142. To the inverting inputs 
of the first, second, third and fourth comparator means 112, 122, 132 and 
142, an output of a maximum value (minimum value) to determining and 
selecting means 100 is applied. Respective comparator means 112, 122, 132 
and 142 compares the inputs and respectively outputs comparator output 
condition signals. The outputs of the comparator means 112, 122, 132 and 
142 are respectively supplied to corresponding ones of the variable 
transmission means 11 21, 31 and 41 so that the variable transmission 
means is controlled into a conducting state in response to H level of the 
corresponding ones of the comparator output condition signals and into a 
non-conducting state in response to L level of the corresponding ones of 
the comparing output condition signals. 
The maximum value determining and selecting means 100 receives the 
receiving condition signals from the receiver means 10, 20, 30 and 40 for 
selecting the best one. Namely, the maximum value determining and 
selecting means 100 selects one of the receiving condition signals having 
the greatest value representing the best receiving condition, to supply 
the selected receiving condition signal to the inverting inputs of 
respective first, second, third and fourth comparator means 112, 122, 132 
and 142. 
Subsequently, the operation of the diversity receiver having the second 
embodiment of the comparator device will be discussed. 
In the construction of the second embodiment, assuming that the receiver 
means 10 is receiving in the best condition among other receiver means, 
the receiving condition signal of the receiver means 10 becomes the 
greatest among the receiving condition signals. Accordingly, the maximum 
value determining and selecting means 100 selects the receiving condition 
signal from the receiver means 10 and outputs the same for the inverting 
inputs of respective ones of the first to fourth comparator means 112, 
122, 132 and 142. 
In this case, when the best receiving condition signal is applied to the 
inverting input of the first comparator means 112 from the maximum value 
determining and selecting means 100, the output of the first comparator 
means 112 becomes H because the receiving condition signal from the 
receiver means 10 is directly applied to its non-inverting input and the 
first comparator means has the offset characteristics as set forth above. 
Therefore, the first variable transmission means 11 is controlled into the 
conducting state to supply the demodulated output of the receiver means 10 
to the output terminal 14. 
On the other hand, when a difference between the receiving condition signal 
of the second receiver means 20 and the selected receiving signal from the 
maximum value determined and selecting means 100, i.e. the receiving 
signal of the first receiver means 10, is smaller than the offset value, 
the output of the second comparator means 122 also becomes H level. In 
such case, the corresponding second variable transmission means 21 is 
controlled into the conducting state to supply the demodulated output of 
the second receiver means 20 to the output terminal 14 in parallel to that 
of the receiver means 10 through the first variable transmission means. 
Such condition of parallel transmission of the demodulated outputs can 
also be temporarily established upon transition for switching the 
demodulated output to be supplied to the output terminal in response to 
the substantial change of the receiving condition signals. 
As described above, in the construction of the second embodiment as set 
forth above, and similarly to the foregoing first embodiment, the 
comparator means comprises the first to fourth comparator means having 
offset characteristics and the hysteresis characteristics so that, when 
one of the input signals is taken as a reference, both of the threshold 
values for the other input signal become greater than the reference value. 
Therefore, there is no possibility of occurrence that all of the first to 
fourth variable transmission means are placed in the non-conducting state 
simultaneously at any combination of four input signals. Also, at the 
transition for switching, a plurality of demodulated outputs can be 
temporarily transmitted simultaneously so that the signal drop out and 
click noise due to delay of operation of the transmission means can be 
effectively eliminated. 
Here, though the first and second embodiments are provided receiving 
condition signals which increase the signal levels at better receiving 
condition, it may be possible to provide a receiving condition signal 
which decreases the signal level at better receiving condition. In such 
case, the polarities of the inputs for the comparators and offsets become 
reversed. In addition, in case of the second embodiment, the maximum value 
determining and selecting means is replaced with a minimum value 
determining and selecting means for selecting the smallest value of the 
receiving condition signal as output for the comparator means. Such 
arrangement will provide completely the same effect as that discussed 
above. 
Furthermore, in the foregoing first and second embodiments as set forth 
above, each comparator means is designed to be responsive to a difference 
of the input voltages. Namely, assuming the input voltage at the 
non-inverting input is taken as a reference, the values of the hysteresis 
and the offset are set as a difference from this reference. Therefore, 
even when the reference changes the value significantly, the hysteresis 
and the offset may have approximately equal difference relative to the 
reference. Such setting is adapted for the case, in which a signal 
indicative of the intensity of the received signal associated with an 
intermediate frequency amplifier IC (such as SIGNETICS Co. NE614) used in 
the receiver means, is used as the receiving condition signal of the 
receiver means. This is because that the signal indicative of the 
intensity of the received signal is obtained as an approximated voltage 
for log value of the amplitude of the received signal, and therefore, can 
be at the same decibel value at any range as converted into the amplitude 
of the input receiving signal of the receiver means as long as the voltage 
difference is the same even when the voltage changes significantly. 
Here, if the receiving condition signal of the receiver means varies 
linearly corresponding to variation of the amplitude of the input 
receiving signal of the receiver means, the values of the hysteresis and 
the offset of the comparator means has to be set as a ratio relative to 
the reference. Namely, the offset value and the hysteresis value must have 
characteristics to be greater or smaller in decibel level so that 
approximately the same ratio can be maintained relative to the reference 
even when the reference changes substantially. By providing such 
characteristics for the offset value and the hysteresis value, the first 
and second embodiment of the comparator devices become applicable for the 
receiving condition signal of the receiver means linearly corresponding to 
the input receiving signal amplitude. Therefore, it should be appreciated 
that the hysteresis and offset may be provided as the difference or ratio 
relative to the reference with one of the inputs being taken as a 
reference. In either case, the comparator device according to the present 
invention may provide substantially the same effect. 
In addition, though the foregoing first and second embodiments are 
constructed to have the comparator means which compares the input 
voltages, the comparator means can be replaced with a comparator means 
which compares input currents. Even in the latter case, although the 
manner of comparison becomes different, the comparator device with the 
current comparison type comparator means can provide substantially the 
same effect to that discussed above. One example is shown in FIG. 6. 
FIG. 6 is a block diagram of the diversity receiver system including a 
plurality of receiver means, for which the third embodiment of the 
comparator device, according to the invention, is applied. In the case of 
this third embodiment, in place of the voltage comparison type first and 
second comparator means 112 and 122 as in the first embodiment, current 
comparison type first and second comparator means 212 and 222, which 
comprise constant current source 213 and 223 and comparator 214 and 224, 
are employed. In this third embodiment, the comparison is thus made with 
respect to current. 
Namely, the receiving condition signal output from the first and second 
receiver means 210 and 220 are both current signals. Each of the receiver 
means 210 and 220 outputs two current signals having the same magnitude. 
Each receiver means 210 and 220 supplies one of the current output of the 
receiver means to the corresponding one of the comparators means 212 and 
222 for controlling transmission of the demodulated signal output 
therefrom, and supplies the other current output to the other comparator 
means 222 and 212 for controlling transmission of the demodulated signal 
output from the other receiver means. 
In the case of the voltage comparison type as in the first embodiment of 
FIG. 3, since the receiving condition signal is the voltage signal and 
thus can be easily delivered to a plurality of destination elements, i.e. 
comparator means, it may require a single output. In contrast to this, in 
the case of the current comparison type comparator means, transmission can 
be made through a single terminal and this can avoid influence of the 
grounding voltage level. Such property is considered suitable for setting 
the hysteresis and offset as the ratios. On the other hand, delivery of 
the current output for a plurality of destination elements requires a 
corresponding number of outputs. Similarly, the voltage comparison type 
comparator means in the second embodiment of the comparator device shown 
in FIG. 5 can be replaced with a current comparison type comparator means. 
In such case, each receiver means is provided two outputs for the 
receiving condition signal so that the one current output is supplied to 
the maximum value determining and selecting means and the other current 
output is supplied to the corresponding comparator means. The maximum 
(minimum) value determining and selecting means is provided outputs 
corresponding to the number of receiving condition signals input thereto. 
Nevertheless, with the current comparison type comparator means in either 
of these cases, the comparator device can provide substantially the same 
effect as that of the former embodiments. 
Considering the first and second embodiment of FIGS. 3 and 5, the receiver 
means, the comparator means, the variable transmission means forming each 
receiving channel are identical to one another. Therefore, these elements 
can be combined into one receiving unit. With respect to the receiving 
unit thus constructed, the receiving signal input terminal to be connected 
to the antenna, the output terminal at the receiver means, the other input 
terminal at the comparator means to be connected to the receiving means in 
other receiving unit, the output terminal at the variable transmission 
means are provided for forming into a single module. By providing common 
specification for such module, it becomes applicable for mass-production 
process for lowering production cost. In this case, the first embodiment 
of the comparator device can be formulated simply by connecting two 
modules. Also, by providing the desired number of modules of the receiving 
units, and the signal maximum (minimum) value determining and selecting 
means, the second embodiment of the comparator device can be formulated 
through a simple process at low cost. Furthermore, by forming the major 
elements, such as the intermediate frequency amplifier, the receiving 
condition signal generator, the comparator means, and the variable 
transmission means in the receiving unit, on a semiconductor integrated 
circuit board, designing and production of the module of the receiving 
unit become simpler and easier. 
Moreover, regarding the maximum value (minimum value) determining and 
selecting means 100 and other cooperating elements in FIG. 5, it should be 
noted that each offset voltage source 13, 23, 33 and 43 sets a voltage 
difference between the input level and a receiving condition signal output 
from the receiver means. The receiving condition signal indicates the 
receiving condition of the receiver means, and it may have characteristics 
so as to be greater for better receiving conditions, as described above. 
Additionally, it may be possible to provide a receiving condition signal, 
the signal level of which decreases for better receiving conditions, also 
as described above. Moreover, as noted above, the receiving condition 
signal may be a signal indicating the intensity of the received signal 
associated with an intermediate frequency amplifier IC (such as SIGNETICS 
Co. NE6114) used in the receiver means, which signal is obtained as the 
approximated voltage for log value of the amplitude of the received 
signal. The maximum value determining and selecting means 100 selects the 
one of the receiving condition signals having the greatest value. Also, 
the maximum value determining and selecting means 100 may be constructed 
by using an analog switch and usual comparators or discrete diodes and a 
transistor, for example. The maximum value is determined and selected 
continuously because the maximum value determining and selecting means 100 
operates on the basis of current levels of the plurality of receiving 
condition signals. 
On the other hand, the maximum value determining and selecting means 100 
can be replaced with a minimum value determining and selecting means for 
selecting the smallest value of the receiving condition signal, as 
described above. 
It should further be noted that the output of each comparator is a signal 
having a H (high) level or L (low) level. 
From the above, it is apparent that the comparator device according to the 
present claimed invention comprises a plurality of comparator means, each 
having an offset characteristic and a hysteresis characteristic as 
described above. These features provide the advantage of reducing 
operational errors resulting from noise and the like. The offset level of 
each comparator, for example, may be larger than one half of the width of 
the hysteresis input level so as to output a binary signal having a preset 
one of the first and second values when the level of the signal applied to 
the first terminal is equal to the level of the signal applied to the 
second terminal, as illustrated in FIGS. 7B-7E which illustrate the basic 
configuration of each of the first through eighth cases discussed above, 
with the operation of the comparator means as shown in FIG. 7A. 
It should be noted that the above description and the accompanying drawings 
are merely illustrative of the application of the principles of the 
present invention and are not limiting. Numerous substitutions, 
modifications, alternatives and variations which embody the principles of 
the invention and which fall within its spirit and scope may be devised by 
those skilled in the art in light of the above teachings.