Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2000-12-04
2003-04-08
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S492000
Reexamination Certificate
active
06543690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic devices for use with a universal serial bus (USB). More particularly, the invention relates to circuitry that improves common mode performance of transmitters or receivers, such as in USB-compatible devices, and facilitates connection of devices, such as USB devices, to a host.
2. Description of Related Art
A number of standard interfaces exist for communicating between a host and a device. Referring to
FIG. 1
, a conventional information handling system
100
is shown. The system
100
makes use of the universal serial bus (“USB”)
125
for connecting a host computer
170
(also known simply as a “host”) to a number of devices, known as USB devices, such as a display
135
, printer
140
, keyboard
145
, trackball
150
, optical scanner
155
, disk drive
160
and other such device
165
. Each one of the devices
135
,
140
, etc. is coupled to the USB
125
via respective ports
130
of the hub
110
.
The USB is currently defined by the Universal Serial Bus Specification written and controlled by USB Implementers Forum, Inc., a non-profit corporation founded by the group of companies that developed the USB Specification. In particular, Universal Serial Bus Specification, revision 1.1, dated Sep. 23, 1998 (the “USB Specification”), Chapter 5 “USB Data Flow Model,” Chapter 7 “Electrical,” and Chapter 8 “Protocol Layer” are hereby incorporated herein by reference.
According to the USB Specification 1.1, USB devices may include both low speed and full speed devices. Low speed devices transfer data at a transmission rate of 1.5 MHz and full speed devices transfer data at a rate of 12 MHz. Data are transmitted on communication lines. That is, the USB device transmits a differential output signal or receives a differential input signal on these communication lines. In the low speed mode, the differential signal indicates a first logical state, referred to as the “J” state, if D+ is at a voltage level below that of D−, and a second state, the “K” state, if D+ is at a voltage level above that of D−. In the full speed mode, the differential signal indicates a first state, the “K” state, if D+ is at a voltage level below that of D−, and a second state, the “J” state, if D+ is at a voltage level above that of D−. The differential design gives better protection against ground shifts and noise since the received signal level is determined by comparing two voltage levels that are both subject to ground shifts or noise affecting both of the differential signals in a similar manner.
A host
170
detects the presence of a device, such as device
165
, on the USB
125
during an attachment phase, while drivers of the port
130
and device are in tri-state. Detection of the attachment is based on a certain connection on the port
130
of a pull-up resistor
210
associated with the device. Likewise, detection of whether the device is operating in low or full speed mode also depends on the pull-up resistor connection.
Referring now to FIG's
2
and
3
,
FIG. 2
shows a transmitter
230
of a typical USB device, of the low speed variety, coupled to a receiver
240
on the corresponding port
130
.
FIG. 3
shows a transmitter
230
of a typical USB device, of the full speed variety, coupled to a receiver
240
of the corresponding port
130
. The low speed device (
FIG. 2
) pull-up resistor
210
is connected between positive voltage contact
213
and the D− signal line
212
. The full speed device (
FIG. 3
) has the pull-up resistor
210
connected between the positive voltage contact
213
and the D+ signal line
215
. Note that according to the USB Specification, the voltage level of
211
supplying the pull-up resistor is different than that of the specified voltage supplied by the port
130
on the signal line
220
by V
BUS
. Thus, the resistor, for example, which is conventionally external to integrated circuitry of the USB device in the prior art, is supplied by its own voltage contact
213
, and not the V
BUS
line
220
, unless additional circuitry is also included coupled to the line
220
to condition the voltage for supplying the pull-up resistor.
The presence of the pull-up resistor on only the D− signal line
212
, for low speed peripherals, or on only the D+ signal line
215
, for full speed peripherals, introduces an imbalance in the symmetry of the differential signal from the USB transmitter
230
, that is, outputs on the signal lines. In other words, due to the resistor, the amplitudes of the signal swings on the signal lines are not the same and the signals do not change at the same rate. This asymmetry is problematic for several reasons, including increases in EMI/RFI radiation, received bit length variation and data stream skew. Aspects of these problems are addressed in U.S. Pat. Nos. 5,905,389 and 5,912,569 (the “Alleven patents”) by introducing a delay circuit in one of the two USB transmitters. While this mitigates the problems, it does not fully eliminate the imbalance in the differential signal arising from the single pull-up resistor.
The presence of the pull-up resistor on one of the communication lines also gives rise to other issues. One issue concerns power consumption by the peripheral. U.S. Pat. No. 6,076,119 (the “Maemura et al. patent”) introduces a switch between the pull-up resistor and a terminal voltage, wherein the switch selectively disconnects the pull-up resistor when a device is inoperative. This reduces power consumption, and also simplifies determination by a host computer that a physically connected USB device is inoperative, but it does not address the imbalance in differential signal arising from connection of the single pull-up resistor during operation of the device.
Another issue concerns suitability for use of “smart cards” in connection with a USB. Referring now to
FIG. 4
, a smart card
400
is shown which has an integrated circuit module (“ICM”)
420
affixed to a card
410
. Although conventional USB peripherals have the USB required pull-up resistor mounted externally, it is problematic to mount a resistor on the surface of a smart card, which is carried in a wallet or purse and repeatedly inserted and removed from a reader. Furthermore, since smart cards compatible with ISO7816 standard are in widespread use in Europe and Asia, legacy issues limit the number of contacts on the smart card which are available for USB applications of smart cards This also gives rise to difficulties in connecting an external resistor to a smart card.
In addition to the above described problems associated with surface mounting and terminal limitations on smart cards, the conventional USB pull-up resistor is also problematic for readers used with smart cards in single-user applications. For relatively centralized applications, such as transactions with payphones, automatic teller machines or point of sale terminals, the number of transactions per smart card reader is high. That is, in these applications each smart card reader is shared by many users, the frequency of transactions per reader is very high, and the cost of the readers is not a major factor. However, smart cards are also useful for widely distributed transactions conducted via the Internet, such as for financial transactions or for logging securely onto a network. For this application, transactions are commonly associated with individual use of computers in homes and offices, and accordingly, smart card readers in this application are used relatively much less frequently, so that the cost per reader is a significant feasibility factor since the solution cost is equal to the smart card reader cost plus the smart card cost.
To overcome the aforementioned problem of USB terminal limitations on ISO7816 compatible smart cards, the use of a conventional USB device's external pull-up resistor requires voltage conditioning circuitry external to the smart card, as described hereinabove. This pull-up resistor and voltage condition
Leydier Robert Antoine
Pomet Alain Christophe
Caputo Lisa M.
Jansson Pehr B.
Le Thien M.
Schlumberger Malco Inc.
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