Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Nonlinear amplifying circuit
Reexamination Certificate
2002-08-22
2003-11-25
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Nonlinear amplifying circuit
Reexamination Certificate
active
06653892
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a squelch circuit to create a squelch waveform prescribed in the universal serial bus 2.0; and, more particularly, to a squelch circuit capable of detecting whether an absolute value of input voltage is over a specific voltage difference or not.
DESCRIPTION OF THE RELATED ART
Generally, a squelch circuit has been used to reduce noises of signals received from telecommunication equipments. For example, when a noise of input signals is over a specific value, the squelch circuit in a receiver stops receiving the signals in order that the input noise from outside is not outputted through an output terminal in the receiver and it automatically blocks the power of the receiver. Further, in other fields, the squelch circuit has been widely used in various circuits, which are required to output a signal when it is over a specific value.
In the universal serial bus (hereinafter, referred to as USB), the squelch circuit detects an input signal that is over a specific voltage difference and then outputs a squelch signal, the USB operates in a high-speed mode.
Referring to
FIG. 1
, a conventional squelch circuit includes a detector and an output unit
20
. The detector
10
determines whether a voltage difference between two input signals (dummy input data) Din and DinB is over a specific value. The detector
10
includes: a buffer U
1
receiving the two input signals Din and DinB and then outputting an output signal having a hysteresis characteristic; an AND gate U
3
combining the output signal from the buffer U
1
and an inverted output signal via a delay inverter U
2
; and a diode U
4
connected in series to the AND gate U
3
.
The output unit
20
receiving an output signal from the diode U
4
includes a resistor R
1
, a capacitor C
1
and an output buffer U
5
. The resistor R
1
and the capacitor C
1
are provided to determine whether a voltage difference between the output signals from the output buffer U
5
and the input signal from the diode U
4
is maintained at a specific value.
Referring to
FIG. 2
, when the voltage difference between the two input signal Din and DinB is over a specific value (V
1
), the input buffer U
1
outputs an output signal having a hysteresis characteristic. The output signal from the input buffer U
1
is inverted via the delay inverter U
2
and the output signals from both the input buffer U
1
and the delay inverter U
2
undergoes a logic multiplication in the AND gate U
3
, thereby forming one-shot-pulses with a shorten pulse width. These one-shot-pulses are continuously transferred to the output unit
20
via the diode U
4
. Accordingly, an input voltage of the output buffer U
5
, which is over a specific value, is made by these transferred pulses. If the input voltage of the output buffer U
5
is over a specific value, a squelch signal is created in a high voltage level in the output unit
20
, and if not, it is created in a low voltage level in the output unit
20
.
As a result, if the voltage difference between two input data is V
1
, a logic high squelch is issued and if the voltage difference between two input data is −V
1
, a logic low squelch is issued.
FIG. 2
is a waveform of the typical squelch signal.
However, the squelch signal required in USB 2.0, which is issued when an absolute value is over a specific value, cannot be provided by the squelch circuit of FIG.
1
.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a squelch circuit in compliance with the specifications of USB 2.0.
It is another object of the present invention to provide, a squelch circuit, which is not dependant on a common mode voltage of input signals and then has a wide operating range for the input signals.
In accordance with an aspect of the present invention, there is provided a squelch circuit comprising: a first differential amplifier for receiving first and second input signals, for sensing a first voltage difference between the first and second input signals and for outputting a first sensing signal when the first voltage difference is over a specific positive value; a second differential amplifier for receiving the first and second input signals, for sensing a second voltage difference between the first and second input signals and for outputting a second sensing signal when the second voltage difference is over a specific negative value; an offset current determining unit coupled to the first and second differential amplifiers for respectively controlling first and second offset currents of the first and second differential amplifiers to determine the specific positive and negative values; and an output unit for outputting a squelch signal in response to the first and second sensing signals.
In accordance with another aspect of the present invention, there is provided a squelch circuit comprising: a first differential amplifier for receiving first and second input signals, for sensing a first voltage difference between the first and second input signals and for outputting a first sensing signal when the first voltage difference is over a specific positive value; a second differential amplifier for receiving the first and second input signals, for sensing a second voltage difference between the first and second input signals and for outputting a second sensing signal when the second voltage difference is over a specific negative value; a first current path coupled to the first differential amplifier for by-passing an offset current of the first differential amplifier to determine the specific positive value in response to the first and second input signals; a second current path coupled to the second differential amplifier for by-passing an offset current of the second differential amplifier to determine the specific negative value in response to the first and second input signals; and an output unit for outputting a squelch signal in response to the first and second sensing signals.
REFERENCES:
patent: 6194920 (2001-02-01), Oguri
patent: 6466085 (2002-10-01), Setty
Hynix / Semiconductor Inc.
Marshall & Gerstein & Borun LLP
Zweizig Jeffrey
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