Voltage output driver and filter

Details Voltage output driver and filter Voltage output driver and filter

2000-07-12

2001-11-13

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

Reexamination Certificate

active

06316927

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of line communications and more particularly to a line driver with waveform-shaping capability.
BACKGROUND OF THE INVENTION
In the line communications environment, line drivers are key components for interfacing with and driving signals along a communications line. It is important to filter or shape the output waveform of a line driver to minimize the amount of frequency interference to satisfy FCC requirements or other regulations and/or the specification set by the manufacturer. Waveform-shaping techniques are performed in the time domain, while waveform filtering is performed in the frequency domain.
In one conventional approach, an external filter is coupled to the driver output. However, this conventional approach increases the cost due to the filter component.
In another conventional approach, on-chip filtering is used but requires a near-unity gain analog output buffer to preserve the internally-filtered waveform and to drive the waveform along a communications line. Thus, this conventional approach also requires the additional output buffer that leads to a die size increase and to additional power requirements. As data transmission rates increase to 100 megahertz or greater, suitable analog output buffers with wide bandwidth and high driving capability become extremely difficult to design and too costly to implement (due to increased power and die size requirements).
Therefore, here is a need for an improved output driver that overcomes the foregoing deficiencies and that could operate under low power and be implemented in a much smaller die size. The present invention achieves the above advantages by merging the filter function into the driver stage.
SUMMARY TO THE INVENTION
The present invention provides an apparatus and method for integrating the functions of driving and filtering signals on a communication line over a wide band of signal frequencies. In one aspect of the present invention, an output current driver includes, an operational amplifier having a first input for receiving a first input voltage V
1
, a second input for receiving a second input voltage V
2
, and an output for generating an output voltage Vc. The output: driver also includes a transistor having an input terminal coupled to the output of the operational amplifier for receiving the output voltage Vc, a first terminal coupled to a differential pair, and a second terminal coupled to the second input of the operational amplifier, wherein an output current I
out
flows across the transistor. A control current I
CONTROL
determines a value of the first input voltage V
1
, while the output voltage Vc controls the transistor so that the second voltage V
2
becomes equal to the first voltage V
1
.
In another aspect of the present invention, a voltage driver includes, a first plurality of parallel modules coupled to an output load and capable of setting a first equivalent resistive value and a second equivalent resistive value. The voltage driver further includes a second plurality of parallel modules coupled to the output load and capable of setting a third equivalent resistive value and a fourth equivalent resistive value, wherein at least some of the equivalent resistive values determine an output voltage value across the output load.
The present invention provides output drivers (voltage drive and current drive) that deliver both accurate (voltage/current) output drive and precision filter performance. With an on-chip-tracking scheme, the output driver of the present invention is insensitive to fabrication process, supply voltage, and temperature variations. The present invention is very suitable for low supply voltage operation. The output voltage driver embodiment utilizes the whole supply voltage range, while the output current driver embodiment has low voltage swing limited to a drain-to-source voltage, V
DS(saturation)
, above ground and can support a high voltage swing to rise above the supply rail provided with external pull up current. These drivers can be segmented to incorporate a multi-phase design that improves filter resolution without requiring an increase in clock rate. The segment on/off control sequence follows the algorithm of FIR (finite impulse response) filter that is well proven and readily available. The present invention is useful in various applications such as line drivers, transceivers, modems and other data communication devices.


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Orsatti, Paulo, et al., “A 20 mA-receive 55 mA-transmit GSM transceiver in 0.25 /spl mu/m CMOS”, Solid-State Circuits Conference (Feb. 15-17, 1999), Digest of Technical Papers, ISSCC. 1999 IEEE International, pp. 232-233 and 464.

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