Output driver for an integrated circuit

Details Output driver for an integrated circuit Output driver for an integrated circuit

2002-07-18

2003-12-16

Tran, Toan (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

C327S563000, C330S258000

Reexamination Certificate

active

06664814

ABSTRACT:

BACKGROUND AND SUMMARY
Generally, when interconnecting integrated circuits (ICs), output drivers are used to drive the output signal of one IC to be received by another IC, as illustrated in
FIG. 1. A
conventional IC
1
generates an IC signal and an output driver
2
receives the IC signal and generates a corresponding output signal that can be received and read by another IC.
For high-speed IC designs, a common type of output driver
2
is a serial line driver, which receives the IC signal and drives the output signal in a serial manner. Turning to
FIG. 2
, a portion of a conventional serial line driver
10
is shown. The driver
10
includes two n-channel metal-oxide semiconductor field-effect transistors (NMOSs)
50
, which receive the IC signal at the gates
60
of the transistors
50
as a differential input signal, i.e., the input signal is the voltage difference between the gates
60
. In the case of an IC
1
generating digital signals, e.g., 1's and 0's, the input signal may be either a high voltage on one gate
60
and a low voltage on the other gate
60
or vice versa and may swing between the two values depending on the signal that the IC
1
generates.
The output signal
40
is generated as a differential output signal at the drains
35
of the transistors
50
—the output signal is the termination voltage difference between the drains
35
. In the case of an IC
1
generating digital signals, the output signal may swing between a first value and a second value depending on the input signal, as described above. A common power supply
20
provides the termination voltage at the drains
35
through two equal valued resistors
30
—typically around 50 ohms—one at each drain
35
. A common current source
70
, represented as a transistor, is coupled to the sources
45
of the transistors
50
and controls the voltage output swing of the output signal
40
—the peak-to-peak voltage of the output signal
40
.
There are several different industry input/output (I/O) standards for the differential output signal
40
, such as the low voltage differential signaling (LVDS) and the low voltage transistor to transistor logic (LVTTL), and many of these standards are incompatible with each other. For example, output signals
40
conforming to one standard may have a different common mode voltage—referring to
FIG. 2
, the common mode voltage is the average voltage across the output signal
40
, i.e., between the two drains
35
—or a different output swing compared to other standards.
Most of the existing output drivers
2
conform only to a single I/O standard. However, there are some applications, such as programmable gate arrays (PGAs) where it may be. desirable to have output drivers that conform to several different standards.
The present invention provides a method and mechanism for driving the output signal of an integrated circuit. According to an embodiment, the common mode voltage and the output swing of a differential output signal generated by an output driver may be programmable.
According to another embodiment, a first power supply is used to supply the termination voltage of the output signal, and a second power supply is used to adjust the common mode voltage.


REFERENCES:
patent: 4105942 (1978-08-01), Henry
patent: 4528517 (1985-07-01), Schlotzhauer
patent: 5990743 (1999-11-01), Gabara
patent: 6064261 (2000-05-01), Stein et al.
patent: 6265941 (2001-07-01), Lopata

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