UNIVERSAL SERIAL BUS TRANSCEIVER

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.

Inventors: MAZER LAWRENCE S, MAZER, LAWRENCE, S.
Applicants: MICREL INC, MICREL, INC.
Application year: 1999
Main classification: G06F13
IPC codes: G06F13, H04L25