Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-08-04
2001-07-17
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S403000, C327S362000
Reexamination Certificate
active
06262606
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to circuits. More particularly, it relates to an output driver having characteristics that can be adjusted based on the waveform being provided to the driver.
An output driver is commonly used to provide drive capability for an output of an integrated circuit. The required drive capability is typically dependent on the load capacitance and impedance associated with the output line being driven and applicable design specifications. The output driver can be designed and operated with higher output current to drive more load capacitance.
Output drivers are used for various integrated circuits such as application specific integrated circuits (ASICs), digital signal processors, microprocessors, controllers, memory devices, and so on. These integrated circuits are used for a wide variety of applications including computing, networking, communication, data transmission, and others.
For many applications, the data provided to the output driver is random and can be any sequence of zeros and ones. During periods in which the data changes often between zero and one, the time between transitions is shorter and the output driver appears to be switched at a high rate. Conversely, during periods in which there is a long sequence of zeros or ones, the time between transitions is longer and the output driver appears to be switched at a lower rate.
For an output driver having a fixed output drive capability, the characteristics of the output waveform can vary depending on the particular data sequence being provided to the driver. During periods of frequent data transitions, a shorter time duration is available for each transition and the output signal may not be able to completely transition from a starting level to a final level. The peak-to-peak signal swing may thus be smaller during such periods of frequent data transition. Conversely, during periods of less frequent data transitions, a longer time duration is available for each transition and the output signal may be able to completely transition from the starting level to the final level. The peak-to-peak signal swing may thus be greater because more time is available to complete the transition. However, for the next data transition, the signal is starting from a higher (or lower) level and would therefore require a longer time period to transition to a mid-point (see
FIGS. 5A and 5B
, which are described below). Thus, a skew exists between a frequently switched signal and a less frequently switched signal. This skew translates to inter-symbol interference (ISI), which in turn can cause detection error at a receiving device.
For some applications, it is desirable to provide an output signal having a reduced amount of skew regardless of the data sequence being driven. This may improve the detection of the data at the receiving device. Thus, an output driver having characteristics that can be adjusted based on the received data sequence to provide an output signal having reduced amount of skew is highly desirable.
SUMMARY OF THE INVENTION
The invention provides an output driver capable of providing reduced amount of skew in the output signal for improved performance. As recognized by the present invention, the amount of skew may be dependent on the data pattern being provided to the output driver. Thus, the invention detects for patterns of interest in the input data signal and appropriately adjusts certain characteristics of the output signal to reduce the amount of skew.
An embodiment of the invention provides an output driver that includes a waveform detector and a driver unit. The waveform detector receives at least one data signal, detects for particular patterns of interest within the received data signal, and provides one or more control signals indicative of detection of patterns of interest in the received data signal. The driver unit receives the data signal and provides at least one output signal in response thereto. The driver unit further receives the control signal(s) and adjusts one or more characteristics of the output signal in accordance with the received control signal(s).
Various characteristics of the output signal can be adjusted to achieve the desired result (e.g., reduced amount of skew and ISI). For example, the slew rate, delay, drive strength, and other characteristics of the output signal can be adjusted based on the detected patterns of interest.
The driver unit can be designed to include a pre-driver coupled to a driver. The pre-driver receives the data signal and provides at least one pre-drive signal in response thereto. The pre-driver can further receive the control signal(s) and adjust one or more characteristics of the pre-drive signal in accordance with the received control signal(s). The driver receives the pre-drive signal and provides the output signal in response thereto. The driver can also be designed to receive the control signal(s) and directly adjust one or more characteristics of the output signal in response.
The pre-driver typically includes at least one pre-driver circuit, one circuit for each output signal. Each pre-driver circuit can include a number of output circuits and can provide different drive strengths. One or more output circuits within each pre-driver circuit can be selectively disabled and enabled, based on a received control signal, to adjust the characteristics of the pre-drive signal being provided by the pre-driver circuit.
Each pre-driver circuit can further include a transmission gate and a switch. The transmission gate receives a control signal and a data signal and either passes or blocks the received data signal based on the received control signal. The switch also receives the control signal and selectively pulls an input of the pre-driver circuit to either logic high or logic low, again based on the received control signal.
The waveform detector can be designed to detect any patterns of interest. Typically, sequences of a particular number of (e.g., 2, 3, or more) consecutive zeros or ones are detected and used to generate the control signal(s). The waveform detector can include at least one set of delay elements, a pattern detector, and a control signal generator. One set of delay elements can be used to provide delay for each data signal. The pattern detector receives the delayed data signals and generates a set of intermediate signals indicative of the detected patterns of interest. The control signal generator receives the set of intermediate signals and generates the control signal(s).
Another embodiment of the invention provides a method for adjusting one or more characteristics of an output signal. In accordance with the method, at least one data signal is received and at least one output signal is provided in response thereto. Patterns of interest within the received data signal are detected and one or more control signals indicative of the detected patterns of interest are generated. One or more characteristics of the output signal are adjusted in accordance with the received control signal(s). Similar to that described above, various characteristics of the output signal (e.g., slew rate, delay, drive strength, and so on) can be adjusted based on the detected patterns to achieved the desired results (e.g., reduced amount of skew and ISI).
Various other aspects and features of the invention are also provided, as described in further detail below.
The foregoing, together with other aspects of this invention, will become more apparent when referring to the following specification, claims, and accompanying drawings.
REFERENCES:
patent: 4945267 (1990-07-01), Galbraith
patent: 5003560 (1991-03-01), Kim
patent: 5373508 (1994-12-01), Guliani
patent: 5504761 (1996-04-01), Shinbashi et al.
patent: 5642063 (1997-06-01), Lehikolnen
patent: 5883534 (1999-03-01), Kondoh et al.
patent: 6181730 (2001-01-01), Negi
Dinh & Associates
Dolphin Technology, Inc.
Tran Toan
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