WO2000031650A1

WO2000031650A1 - Universal serial bus transceiver

Info

Publication number: WO2000031650A1
Application number: PCT/US1999/027166
Authority: WO
Inventors: Lawrence S. Mazer
Original assignee: Micrel, Inc.
Priority date: 1998-11-20
Filing date: 1999-11-16
Publication date: 2000-06-02
Also published as: US6356582B1; EP1131733A1; EP1131733B1

Abstract

A universal serial bus transceiver is disclosed. In one embodiment, the transceiver includes a differential transmitting amplifier with a first input terminal that receives a reference voltage, a second input terminal that receives a first data input signal at a level corresponding to the reference voltage, and a third input terminal that receives a second data input signal at the reference voltage level. The differential transmitting amplifier generates first and second bus data output signal at the bus signal level in response to the first and second data input signals. The transceiver also includes a first receiving amplifier with a first input terminal that receives the reference voltage and a second input terminal that receives a first bus data input signal at the bus signal level. The first receiving amplifier generates a first data output signal at the reference voltage level. Similarly, the transceiver includes a second receiving amplifier with a first input terminal that receives the reference voltage and a second input terminal that receives a second bus data input signal at the bus signal level. The second receiving amplifier generates a second data output signal at the reference voltage level. The disclosed transceiver may reside on a separate chip from the USB controller, eliminating the need for the USB controller to support the universal serial bus signal level. Moreover, the disclosed generic USB transceiver is compatible with a variety of USB controllers utilizing different internal signal levels.

Description

UNIVERSAL SERIAL BUS TRANSCEIVER

TECHNICAL FIELD OF THE INVENTION

The present invention relates to personal computers, and in particular to a

universal serial bus transceiver.

BACKGROUND OF THE INVENTION

A standard has been developed for a universal serial bus (USB) for personal computers. According to this standard, set forth most recently in Universal Serial Bus

Specification Revision 1.1 , a universal serial bus transceiver provides logic signals on

the bus at a signal level of five volts. In order to achieve this required bus signal level,

the transceiver's internal data lines must support voltages as high as 3.8 V.

The transceiver is typically integrated on the same chip with a USB controller.

Thus, since smaller chip designs are not capable of handling larger voltages, the

required internal transceiver voltage place a practical lower limit of approximately 0.5

microns on the design rule for the USB transceiver and controller. This lower limit

severely restricts the ability of chip designers to either increase the functionality or

reduce the chip size of the USB transceiver and controller. In addition, portable devices

such as personal data assistants, palmtop computers and cellular telephones typically

have lower system voltages which cannot easily support the required USB voltages. - SUMMARY OF THE INVENTION

Therefore, a need has arisen for a universal serial bus communication system

that addresses the disadvantages and deficiencies of the prior art. In particular, a need

has arisen for a universal serial bus communication system with separate controller and

transceiver chips, to allow lower system voltage on the transceiver chip.

Accordingly, a novel universal serial bus transceiver is disclosed. In one

embodiment, the transceiver includes a differential transmitting amplifier with a first

input terminal that receives a reference voltage, a second input terminal that receives a

first data input signal at a level corresponding to the reference voltage, and a third input

terminal that receives a second data input signal at the level corresponding to the reference voltage. The differential transmitting amplifier generates first and second bus

data output signal at the bus signal level in response to the first and second data input

signals. The transceiver also includes a first receiving amplifier with a first input

terminal that receives the reference voltage and a second input terminal that receives a

first bus data input signal at the bus signal level. The first receiving amplifier generates

a first data output signal at the level corresponding to the reference voltage. Similarly,

the transceiver includes a second receiving amplifier with a first input terminal that

receives the reference voltage and a second input terminal that receives a second bus

data input signal at the bus signal level. The second receiving amplifier generates a

second data output signal at the level corresponding to the reference voltage.

In another embodiment of the present invention, a USB-compatible electronic

device includes a processor that generates data for transmission on a universal serial

bus. The device also includes a universal serial bus controller, residing on a first

integrated circuit chip, that receives the data for transmission on the universal serial bus -from the processor and provides both a reference voltage and first and second data signals at a signal level associated with the reference voltage in response to the data

received from the processor. The device also includes a universal serial bus transceiver,

residing on a second integrated circuit chip, that receives the reference voltage and the

first and second data signals from the universal serial bus controller and generates, in

response to the first and second data signals received from the universal serial bus

controller, first and second bus data output signals at a bus signal level that is different

from the signal level associated with the reference voltage.

According to still another embodiment of the present invention, a method for

communicating data via a universal serial bus includes receiving a controller reference

voltage at a differential transmitting amplifier, receiving first and second controller data

input signals at a level corresponding to the controller reference voltage at the

differential transmitting amplifier, generating first and second bus data output signals at

a bus signal level by the differential transmitting amplifier in response to the first and

second controller data input signals, the bus signal level being different from the level

corresponding to the controller reference voltage, and transmitting the first and second

bus data output signals on the universal serial bus.

An advantage of the present invention is that the USB controller and USB

transceiver may reside on separate integrated circuit chips, eliminating the need for the

USB controller to support the universal serial bus signal level. Another advantage of

the present invention is that the USB transceiver may be powered entirely by the

universal serial bus voltage, eliminating the need for the power supply for the USB

transceiver. Yet another advantage is that the disclosed generic USB transceiver is

compatible with a variety of USB controllers utilizing different internal signal levels. ^• BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and for further

features and advantages, reference is now made to the following description taken in

conjunction with the accompanying drawings, in which:

FIGURE 1 is a block diagram of a personal computer system constructed in

accordance with the present invention;

FIGURE 2 is a block diagram of a universal serial bus controller for use in the

personal computer system;

FIGURE 3 is a block diagram of a universal serial bus transceiver for use in the personal computer system; and

FIGURE 4 is a schematic diagram of the universal serial bus transceiver.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention and their advantages are

best understood by referring to FIGURES 1 through 6 of the drawings. Like numerals

are used for like and corresponding parts of the various drawings.

Referring to FIGURE 1, a block diagram of a personal computer system 10

constructed in accordance with the present invention is shown. Personal computer

system 10 includes a personal computer 1 1 connected to peripheral devices 12, 14 and

16 by means of a universal serial bus 18. Each peripheral device 12, 14 and 16 may be,

for example, a standard peripheral device such as a printer, keyboard, mouse or

monitor, or a mobile device such as a personal data assistant, palmtop computer, or

cellular telephone. Personal computer 11 acts as the host for universal serial bus 18. For ease of illustration, peripheral device 12 will be described as a "function"

device on universal serial bus 18, meaning that peripheral device 12 does not provide a

hub for the connection of other peripheral devices. However, it will be understood in

the following description that peripheral device 12 need not be solely a "function"

device.

Peripheral device 12 includes a processor 20 such as an Intel x86

microprocessor. Processor 20 communicates with a USB controller 22, which controls

a USB transceiver 24. In accordance with the present invention, USB controller 22 and

USB transceiver 24 reside on separate integrated circuit chips, as will be described

more fully below. A USB connector 25 provides a physical connection between USB

transceiver 24 and universal serial bus 18. Peripheral devices 14 and 16 each also

include a processor, USB controller, USB transceiver and USB connector (not shown)

which may be implemented in accordance with the present invention, as in peripheral device 12. Universal serial bus 18 is a four- wire bus carrying data signals D+ and D-, a

bus voltage line V_BUS and a ground line GND in accordance with USB standards.

Referring to FIGURE 2, a block diagram of USB controller 22 is shown. USB

controller 22 includes a function controller 26 and a serial interface engine 28. USB

controller is powered by an external power supply (not shown) which provides a supply

voltage Nip.

Function controller 26 communicates with processor 20 using an application-

specific data protocol. Function controller 26 receives data from processor 20 for

transmission on universal serial bus 18. Function controller 26 packages this data into

USB-compliant data packets and passes these packets in parallel format to serial

interface engine 28. Serial interface engine 28 performs packet ID generation, cyclic " redundancy check (CRC) generation and parallel-to-serial conversion on the data

packets. Serial interface engine 28 then transmits the data packets on lines 30 through

40 to USB transceiver 24 using non-return to zero inverted (NRZI) data encoding with

bit-stuffing in accordance with USB specifications.

Likewise, serial interface engine 28 receives NRZI-encoded, USB-compliant

data packets from personal computer 11 via universal serial bus 18 and USB transceiver

24. Serial interface engine 28 performs clock/data separation, NRZI decoding, packet

ID decoding and CRC error-checking on the data packets in accordance with USB

standards, and performs serial-to-parallel conversion before transmitting the data

packets to function controller 26. Function controller 26 in turn transmits the data to

processor 20.

Referring to FIGURE 3, a block diagram of USB transceiver 24 is shown. USB

transceiver 24 receives the supply voltage of USB controller 22 as a reference voltage

V_IF via line 30. This reference voltage allows USB transceiver 24 to provide a signal level transition between the required universal serial bus signal level of five volts and

the internal logic signal level of USB controller 22, as will be described more fully

below.

USB transceiver 24 receives a SPEED signal from USB controller 22 via line

32. The SPEED signal determines the slew rate of a transmitting amplifier 43. When

the SPEED signal is high, data communication on universal serial bus 18 is to occur at

12 Mbps, while a low SPEED signal indicates that data communication on universal

serial bus 18 is to occur at 1.5 Mbps. Thus, when the SPEED signal is high,

transmitting amplifier 43 has an output slew time between 4 and 20 nanoseconds. ^• When the SPEED signal is low, transmitting amplifier 43 has an output slew time

between 75 and 300 nanoseconds.

USB transceiver 24 receives serialized data packets as previously described

from serial interface engine 28 of USB controller 22 via data lines 36 and 38. The data

signals on lines 36 and 38 are designated Vp and V_M, respectively. Vp and V_M are

complementary logic signals corresponding to data signals D+ and D-, respectively, on

universal serial bus 18, as will be described more fully below.

USB transceiver 24 receives an output enable signal (OE#) from USB controller

22 via line 40. This logic signal determines whether USB transceiver 24 is currently

transmitting or receiving signals on universal serial bus 18.

USB transceiver 24 receives a universal serial bus supply voltage V_BUS, which may provide power for USB transceiver 24 and other circuitry in peripheral device 12.

This supply voltage is provided by another device on universal serial bus 18, such as

personal computer 11.

A voltage regulator 41 receives the supply voltage V_BUS and distributes power to the circuitry in USB transceiver 24. Voltage regulator 41 also generates a regulated

voltage V_TERM between 3.0 and 3.6 volts. This regulated voltage is used to terminate an

external speed sense resistor 42, which is connected to either the D+ or D- bus data line.

If speed sense resistor 42 is connected to the D+ data line, then USB transceiver 24 is

set for 12 Mbps operation. If speed sense resistor 42 is connected to the D- data line,

then USB transceiver 24 is set for 1.5 Mbps operation.

A ground-level voltage GND is received on bus line 18d. Bus line 18d is

connected to local ground at USB transceiver 24 to provide a common ground. Signals Vp and V_M are supplied to the inputs of a transmitting amplifier 43,

which produces complementary output signals D+ and D- on universal serial bus data

lines 18a and 18b, respectively, in accordance with USB specifications. Transmitting

amplifier 43 receives reference voltage V_JF from USB controller 22 to discriminate the

values of input signals Vp and V_M- However, because signals Vp and V_M are produced

by USB controller 22 at a lower signal level than the USB-specified signal level for

signals D+ and D-, transmitting amplifier 43 amplifies its output signals D+ and D- to

the required signal level.

Transmitting amplifier 43 also receives the output enable signal OE# from USB

controller 22. When signal OE# is low, transmitting amplifier 43 is enabled to produce

output signals D+ and D-, while a high OE# signal causes the output of transmitting

amplifier 43 to present a high impedance so that incoming signals may be received on data lines 18a and 18b.

Data line 18a carrying signal D+ is provided to the input of a receiving amplifier

46. Receiving amplifier 46 receives output enable signal OE# from USB controller 40,

so that the output of receiving amplifier 46 is enabled only when a receiving mode is

indicated by output enable signal OE#. Receiving amplifier 46 also receives reference

voltage V_ΓF SO as to produce a logic output signal Vp at the internal signal level of USB

controller 22. Receiving amplifier 46 may be, for example, a simple Schmitt trigger

with an output level set by reference voltage Vrp.

Likewise, data line 18b carrying signal D- is provided to the input of a receiving

amplifier 48. Receiving amplifier 48 receives output enable signal OE# from USB

controller 40, so that the output of receiving amplifier 48 is enabled only when a

receiving mode is indicated by output enable signal OE#. Receiving amplifier 48 also ^■ receives reference voltage Nn? so as to produce a logic output signal V_M at the internal signal level of USB controller 22. Receiving amplifier 48, like receiving amplifier 46,

may be a simple Schmitt trigger with an output level set by reference voltage Vrp.

Both data lines 18a and 18b are provided to the inputs of a differential receiving

amplifier 44, which produces an output signal RCV on line 34. Output signal RCV

represents the difference between signals D+ and D-. Thus, when D+ is greater than D-

, RCV is HIGH, while RCV is low when D- is greater than D+. Differential receiving

amplifier 44 receives reference voltage Vrp so as to produce output signal RCV at the

internal signal level of USB controller 22.

Referring to FIGURE 4, a schematic diagram of USB transceiver 24 is shown.

FIGURE 4 comprises FIGURES 4A through 4M, FIGURE 4A being an overall

schematic diagram in partial block form of USB transceiver 24 and FIGURES 4B through 4M being expanded schematic diagrams of portions of USB transceiver 24.

USB transceiver 24, as shown in FIGURE 4, utilizes input signals VIF (V_IF), VP (Vp),

VM (V_M), DP (D+), DM (D-), SPEED, OEΝ (OE#) and VTERM, as well as internally

generated bias voltages and other signals, to generate output signals VP (Vp), VM (V_M),

DP (D+), DM (D-) and RCV as previously described with respect to FIGURE 3.

Although the present invention and its advantages have been described in detail,

it should be understood that various changes, substitutions, and alterations can be made

therein without departing from the spirit and scope of the invention as defined by the

appended claims.

Claims

- CLAIMS I claim:

1. A universal serial bus transceiver comprising:

a differential transmitting amplifier having a first input terminal operable to

receive a reference voltage, a second input terminal operable to receive a first data input

signal at a level corresponding to the reference voltage, and a third input terminal

operable to receive a second data input signal at the level corresponding to the reference

voltage, the differential transmitting amplifier being operable to generate a first bus data

output signal at a bus signal level on a first output terminal in response to the first and

second data input signals, the differential transmitting amplifier being further operable

to generate a second bus data output signal at the bus signal level on a second output

terminal in response to the first and second data input signals;

a first receiving amplifier having a first input terminal operable to receive the

reference voltage and a second input terminal operable to receive a first bus data input

signal at the bus signal level, the first receiving amplifier being operable to generate a

first data output signal at the level corresponding to the reference voltage at an output

terminal; and

a second receiving amplifier having a first input terminal operable to receive the

reference voltage and a second input terminal operable to receive a second bus data

input signal at the bus signal level, the second receiving amplifier being operable to

generate a second data output signal at the level corresponding to the reference voltage

at an output terminal.

2. The universal serial bus transceiver of claim 1, wherein the differential transmitting amplifier further comprises a fourth input terminal operable to receive an

output enable signal, the differential transmitting amplifier being operable to generate

the first and second bus data output signals in response to a first state of the output

enable signal, the differential transmitting amplifier being further operable to present a

high impedance at the first and second output terminals in response to a second state of

the output enable signal.

3. The universal serial bus transceiver of claim 2, wherein the first

receiving amplifier further comprises a third input terminal operable to receive the output enable signal, the first receiving amplifier being operable to generate the first

data output signal in response to the second state of the output enable signal, the first

receiving amplifier being further operable to present a high impedance at the output

terminal in response to the first state of the output enable signal.

4. The universal serial bus transceiver of claim 3, wherein the second

receiving amplifier further comprises a third input terminal operable to receive the

output enable signal, the second receiving amplifier being operable to generate the

second data output signal in response to the second state of the output enable signal, the

second receiving amplifier being further operable to present a high impedance at the

output terminal in response to the first state of the output enable signal.

5. The universal serial bus transceiver of claim 1, further comprising a

differential receiving amplifier having first and second input terminals operable to ^" receive the first and second bus data input signals, respectively, and a third input

terminal operable to receive the reference voltage, the differential receiving amplifier

being operable to generate a differential receive signal at the level corresponding to the

reference voltage at an output terminal, the differential receive signal representing a

difference between the first and second bus data input signals.

6. A USB-compatible electronic device comprising:

a processor operable to generate data for transmission on a universal serial bus;

a universal serial bus controller residing on a first integrated circuit chip, the

universal serial bus controller being operable to receive the data for transmission on the

universal serial bus from the processor, the universal serial bus controller being further

operable to generate a reference voltage, and operable to generate first and second data signals at a signal level associated with the reference voltage in response to the data

received from the processor,

a universal serial bus transceiver residing on a second integrated circuit chip, the

universal serial bus transceiver being operable to receive the reference voltage and the

first and second data signals from the universal serial bus controller, and operable to

generate first and second bus data output signals at a bus signal level different from the

signal level associated with the reference voltage, the first and second bus data output

signals being generated at first and second bus output terminals, respectively, the first

and second bus data output signals being generated in response to the first and second

data signals received from the universal serial bus controller.

7. The universal serial bus transceiver of claim 6, further comprising a universal serial bus connector, operable to provide an electrical connection between the

first bus output terminal of the universal serial bus transceiver and a first data line of a

universal serial bus, and operable to provide an electrical connection between the

second bus output terminal of the universal serial bus transceiver and a second data line

of the universal serial bus.

8. A method for communicating data via a universal serial bus, the method

comprising:

receiving a controller reference voltage at a differential transmitting amplifier;

receiving first and second controller data input signals at a level corresponding

to the controller reference voltage at the differential transmitting amplifier;

generating first and second bus data output signals at a bus signal level by the

differential transmitting amplifier in response to the first and second controller data

input signals, the bus signal level being different from the level corresponding to the

controller reference voltage; and

transmitting the first and second bus data output signals on the universal serial bus.

9. The method of claim 8, further comprising:

receiving the controller reference voltage at a first receiving amplifier;

receiving at the first receiving amplifier a first bus data input signal at the bus

signal level from the universal serial bus; generating by the first receiving amplifier a first controller data output signal at

the level corresponding to the controller reference voltage; and

transmitting the first controller data output signal to a universal serial bus

controller by the first receiving amplifier.

10. The method of claim 9, further comprising:

receiving the controller reference voltage at a second receiving amplifier;

receiving at the second receiving amplifier a second bus data input signal at the bus signal level from the universal serial bus;

generating by the second receiving amplifier a second controller data output

signal at the level corresponding to the controller reference voltage; and

transmitting the second controller data output signal to the universal serial bus controller by the second receiving amplifier.

11. The method of claim 10, further comprising:

receiving the controller reference voltage at a differential receiving amplifier;

receiving at the differential receiving amplifier the first and second bus data

input signals from the universal serial bus;

generating by the differential receiving amplifier a differential receive output

signal at the level corresponding to the controller reference voltage; and

transmitting the differential receive output signal to the universal serial bus

controller by the differential receiving amplifier.