Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – With compensation
Reexamination Certificate
1998-10-22
2001-07-10
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
With compensation
C327S538000, C327S355000, C327S560000
Reexamination Certificate
active
06259302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to adaptive signal equalizers for adaptively equalizing high data rate signals received via long lengths of cable, and in particular, to gain controllers for controlling the signal gain of such adaptive signal equalizers.
2. Description of the Related Art
As part of the process of recovering data which has been transmitted over a long length of cable at a high data rate, equalization of the received data signal is required in order to compensate for the loss and phase dispersion characteristics of the cable. For example, referring to
FIG. 1
, the signal losses associated with a cable increase with frequency, and such signal losses become greater as the cable length is increased from a virtually zero length L
0
to greater cable lengths L
1
, L
2
, L
3
, . . . . Therefore, higher order frequency components of the data signal become increasingly attenuated as compared to the lower order frequency components. Accordingly, the degree of signal equalization required increases with frequency as well as cable length.
Further, in those applications where the transmission cable lengths may vary, such equalization must be adaptive by being able to adapt to variations in the transfer function of the cable due to variations in the cable length.
Referring to
FIG. 2
, a conventional adaptive equalizer
20
includes a unity-gain buffer
22
, a high-pass filter
24
, a mixer
26
and a signal summation stage
28
, interconnected as shown. The input signal V
i
is processed by both the unity-gain buffer stage
22
and filtered by the high-pass filter
24
. The high-pass filtered signal
25
is mixed with a gain control signal &agr; in the mixer
26
. The unity-gain buffered signal
23
and gain-controlled, high-pass filtered signal
27
are summed together in the summation circuit
28
to produce the final output signal V
o
.
Referring to
FIG. 3
, it can be seen that by varying the value of the control signal &agr;, the overall gain of the high-pass filter profile can be adjusted, thereby providing for adaptive equalization of the output signal V
o
.
While this conventional technique performs reasonably well, a number of disadvantages exist, particularly when more precise equalization control is desired. For example, depending upon a number of operating parameters of the equalization circuit
20
, such as variations in processing during manufacturing and variations in operating voltages and temperatures, the gain factor &agr; may affect the DC biasing of portions of the circuit
20
. Further, the output signal V
o
may be affected by variations in the DC bias components within the circuit
20
. Accordingly, it would be desirable to have a gain-controlled adaptive equalizer in which the gain factor &agr; is independent of variations in circuit operation due to variations in circuit manufacturing processes and operating voltages and temperatures.
SUMMARY OF THE INVENTION
A gain controller for an adaptive equalizer in accordance with the present invention provides a gain factor which is independent of variations in circuit operation due to variations in circuit manufacturing processes and operating voltages and temperatures. Such a gain controller provides a self-compensating gain control signal which is based upon a variable gain control factor and tracks variations in circuit operation due to variations in circuit manufacturing processes and operating conditions (e.g., voltages and temperatures) by tracking variations in the dc biasing used to power the gain control and signal mixing stages. Such tracking of the biasing by the gain control advantageously provides for an increased dynamic range.
In accordance with one embodiment of the present invention, a gain controller for a signal combining circuit includes a reference signal generator circuit and a signal conversion circuit. The reference signal generator circuit is configured to receive a first bias signal and in accordance therewith provide first and second reference signals. Variations in the first bias signal are tracked by corresponding respective variations in the first and second reference signals. The signal conversion circuit, coupled to the reference signal generator circuit, is configured to receive an input control signal and the first and second reference signals and in accordance therewith provide first and second output control signals. The input control signal has a range of values with a minimum value and a maximum value. The first output control signal has a range of values which correspond to the input control signal values with minimum and maximum values which correspond to the minimum and maximum input control signal values, respectively. The second output control signal has a range of values which correspond to the input control signal values with minimum and maximum values which correspond to the maximum and minimum input control signal values, respectively. The first and second output control signals together form a differential control signal.
In accordance with another embodiment of the present invention, a gain controller for a signal combining circuit includes a reference signal generator circuit and a digital-to-analog signal conversion circuit. The reference signal generator circuit with a plurality of diode-connected transistors configured to receive a first bias current and in accordance therewith provide first and second reference voltages. Variations in the first bias current are tracked by corresponding respective variations in the first and second reference voltages. The digital-to-analog signal conversion circuit, coupled to the reference signal generator circuit, is configured to receive a digital control signal and the first and second reference voltages and in accordance therewith provide first and second analog control voltages. The digital control signal has a range of values with a minimum value and a maximum value. The first analog control voltage has a range of values which correspond to the digital control signal values with minimum and maximum values which correspond to the minimum and maximum digital control signal values, respectively. The second analog control voltage has a range of values which correspond to the digital control signal values with minimum and maximum values which correspond to the maximum and minimum digital control signal values, respectively. The first and second analog control voltages together form a differential control voltage.
In accordance with still another embodiment of the present invention, a method of providing gain control for a signal combining circuit includes the steps of:
receiving a first bias signal and in accordance therewith generating first and second reference signals, wherein variations in the first bias signal are tracked by corresponding respective variations in the first and second reference signals; and
receiving an input control signal and the first and second reference signals and in accordance therewith generating first and second output control signals, wherein
the input control signal has a range of values with a minimum value and a maximum value,
the first output control signal has a range of values which correspond to the input control signal values with minimum and maximum values which correspond to the minimum and maximum input control signal values, respectively,
the second output control signal has a range of values which correspond to the input control signal values with minimum and maximum values which correspond to the maximum and minimum input control signal values, respectively, and
the first and second output control signals together form a differential control signal.
In accordance with yet another embodiment of the present invention, a method of providing gain control for a signal combining circuit includes the steps of:
receiving a first bias current and in accordance therewith generating first and second reference voltages with a plurality of diode-connected transistors, wherein variations in the first bias current are tracked by correspon
Hee Wong
Phanse Abhijit
Baker & McKenzie
Callahan Timothy P.
National Semiconductor Corporation
Nguyen Hai L.
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