Pulse or digital communications – Receivers – Automatic baseline or threshold adjustment
Reexamination Certificate
1997-11-20
2001-01-09
Vo, Don N. (Department: 2734)
Pulse or digital communications
Receivers
Automatic baseline or threshold adjustment
C375S344000
Reexamination Certificate
active
06173018
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention, in a demodulator circuit such as a pager, relates to a control circuit of threshold levels for a multi-level comparator in the demodulator circuit for detecting a multi-level signal with the use of the comparator.
In a demodulator circuit such as a pager, a multi-level comparator is used for receiving and demodulating a multi-level signal and it is practiced therein to compare the signal transmitted through the process of detection and predetermined threshold levels to obtain the desired signal.
FIG.
1
and
FIG. 2
are circuit diagrams explanatory of related art examples. In the circuit shown in
FIG. 1
, a current output of a detector is input to two comparators
1
and
2
through a low-pass filter (LPF) to be compared therein with their respective different threshold levels and, thereby, output data corresponding to the multivalued data is obtained. Further, in the above described circuit, it is adapted such that the average voltage of the detected output is detected in an average voltage detector circuit
4
and the same is fed back to a comparator
5
as its threshold level and, thereby, the operating point of the detected output is shifted.
In the circuit shown in
FIG. 2
, it is adapted such that a detector output is input to two comparators
11
and
12
through a low-pass filter (LPF) to be compared with their respective different threshold levels and, thereby, output data corresponding to the multivalued data is obtained. In this circuit, the average voltage of the detected output is detected in an average voltage detector circuit
13
and, with the use of it, the threshold levels for the comparators
11
and
12
are shifted.
However, there have been problems with such circuits that the signal level is shifted by a deviation in the intermediate frequency and thereby lowering of the sensitivity is incurred, or that the threshold levels for the multi-level comparator become unable to follow changes in the level of the detected output and therefore lowering of the sensitivity is incurred when there arise fluctuations in the devices, changes in the temperature, or changes in the input level.
Further, when identical data or biased data are continuously included in the received data, the average value of the level of the detected output changes and an offset is produced between the threshold levels for the comparators and the operating point of the level of the detected output, and hence problems of lowering in the sensitivity or inability of signal reception arise. Still further, in the case of intermittent signal reception, to decrease the time constant in obtaining the average voltage at a rise of the received signal (quick charging), then, by the setting to shorten the rise period, an error voltage is left according to the timing of the quick charging. A problem then arises that the duty cycle of the output data changes at each instant intermittent signal reception is made.
OBJECT AND SUMMARY OF THE INVENTION
An object of the invention is to allow a multi-level comparator to stably operate in conformity with changes in the level of the input signal. Accordingly, in a demodulator circuit for obtaining output data through comparison, made in a comparator, of a signal obtained by subjecting a received signal to a process of detection in a detector circuit and predetermined threshold levels, there is provided a control circuit of threshold levels for a multi-level comparator in the demodulator circuit which comprises a level detector circuit for detecting the level of the received signal transmitted through the process of detection and a control circuit for controlling relative magnitudes of the level detected in the level detector circuit of the signal transmitted through the process of detection and the predetermined threshold levels for the multi-level comparator.
Since, in the invention, the level of a signal transmitted through a process of detection is detected in the level detector circuit and the detected level of the signal transmitted through the process of detection and the predetermined threshold levels for the multi-level comparator are controlled for their relative magnitudes in the control circuit, it is made possible, even if the signal level is changed, to set the predetermined threshold levels at fixed ratios to the changed signal level.
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Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
Vo Don N.
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