# Patent

## Title
Programmable pre-emphasis circuit for serial ATA

## Abstract

A high-speed serial ATA physical layer transmits data over a communications medium using a serial ATA protocol. A serial ATA control circuit controls operation of the serial ATA physical layer. A serial ATA multiplexer outputs a serial ATA signal and has a plurality of input lines for receiving input data and a control input that communicates with the serial ATA control circuit. A serial ATA analog front end includes a first differential driver that communicates with the serial ATA multiplexer and provides a first gain to the serial ATA signal and a serial ATA pre-emphasis circuit that provides pre-emphasis to the serial ATA signal to alter a transmission characteristic of the serial ATA signal.

## Background
FIELD OF THE INVENTION
The present invention relates to serial ATA communications channels, and more particularly to a programmable pre-emphasis circuit for a serial ATA communications channel.
BACKGROUND OF THE INVENTION
A host and a device typically transmit and receive data to and from each other. For example in a personal computer environment, a disk drive controller (host) is often connected to a disk drive (device). Referring now to FIG. 1A, a host 10 includes a receiver 12 and a transmitter 14. A device 16 includes a receiver 18 and a transmitter 20. The transmitter 14 of the host 10 transmits host data 22 to the receiver 18 of the device 16. The transmitter 20 of the device 16 transmits device data 24 to the receiver 12 of the host 10. In the personal computer environment the host 10 can be a disk controller 10-1 and the device 16 can be a disk drive 16-1 as shown in FIG. 1B. Still other hosts and devices can be employed.
The host and the device are connected using a Serial Advanced Technology Attachment (SATA) standard, which is generally identified at 26. The SATA standard is a simplified packet switching network between a host and a device. SATA typically employs balanced voltage (differential) amplifiers and two pairs of wires that connect transmitters and receivers of the host 10 and the device 16 in a manner similar to 100BASE-TX Ethernet. The SATA standard is disclosed in “Serial ATA: High Speed Serialized AT Attachment”, Serial ATA Organization, Revision 1.0, 29 Aug. 2001, and its Supplements and Errata, which are hereby incorporated by reference.
Referring now to FIG. 1C, a typical physical layer (PHY) 28 of the host 10 and/or the device 16 is shown generally at 29. An analog front end 30 provides an interface to the data transmission lines. The analog front end 30 includes differential drivers and receivers and/or out-of-band signaling circuits. A PHY control circuit 31 controls the functionality of the PHY 28. Fixed pattern source and detect circuits 32 and 33, respectively, are optional circuits that provide ALIGN primitives. The fixed pattern detect circuit 33 generates a COMMA signal when a K28.5 character is detected in the received data.
DataIn[0:n] and an output of the fixed pattern source 32 are input to a multiplexer 34. The PHY control circuit 31 controls the multiplexer 34. DataIn[0:n] includes data sent from the link layer to the PHY 28 for serialization and transmission. A data extraction circuit 35 separates the clock (RecClk clock signal) and data received by the receivers in the analog front end 30. The TxClk output from the control circuit 31 regulates the frequency of the serial stream. DataOut[0:n], which is passed to the link layer, includes data that is received and deserialized by the PHY 28. The SYSCLK signal is a reference clock signal that is used to establish the transmitter interface speed. Other control inputs and outputs generally identified by MISC in FIG. 1C are specified in the SATA standard.
Referring now to FIG. 2, the transmitter 14 of the host 10 or the transmitter 20 of the device 16 is shown. Differential data (D(0)+ and D(0)−) to be transmitted is received by differential inputs of a differential driving device 40. The differential driving device 40 creates a differential voltage (V+ and V−) by driving differential outputs (i0+ and i0−) through loads 42 and 44. A communications channel 46 transmits the differential voltage to the receiver 18 of the device 16 or to the receiver 12 of the host 10. The transmission characteristics of the communications channel 46 may attenuate or otherwise alter the signal that is received by the receiver at the opposite end of the communications channel 46, which may increase bit error rates.
Referring now to FIG. 3, the differential output voltage in an ideal communications channel 46 is shown. In FIG. 4, the differential output voltage of a band-limiting communications channel is shown, which is a typical characteristic of the communications channel 46. The transition from 0 to 1 to 0 creates an “eye”-shaped waveform that is generally identified at 48 in FIGS. 4 and 5. As the band-limiting transmission characteristic increases, the “eye” closes as shown by arrows 49, which makes the 0-1-0 transition more difficult to detect.
SUMMARY OF THE INVENTION
A high-speed serial ATA physical layer according to the present invention transmits data over a communications medium using a serial ATA protocol. A serial ATA control circuit controls operation of the serial ATA physical layer. A serial ATA multiplexer outputs a serial ATA signal and has a plurality of input lines for receiving input data and a control input that communicates with the serial ATA control circuit. A serial ATA analog front end includes a first differential driver that communicates with the serial ATA multiplexer and provides a first gain to the serial ATA signal and a serial ATA pre-emphasis circuit that provides pre-emphasis to the serial ATA signal to alter a transmission characteristic of the serial ATA signal.
In other features, the serial ATA physical layer is implemented in a serial ATA device or a serial ATA host. The first differential driver generates a first amplified signal. The pre-emphasis circuit includes a first delay element that delays the first amplified signal to generate a first delayed signal, a second driver that amplifies the first delayed signal using a second gain to generate a second amplified signal, and a first summing circuit that adds the first amplified signal and the second amplified signal to generate a sum.
In yet other features, the pre-emphasis circuit further includes a second delay element that delays the second amplified signal to generate a second delayed signal. A third driver amplifies the second delayed signal using a third gain to generate a third amplified signal. The summing circuit adds the third amplified signal to the sum.
In still other features, the pre-emphasis circuit further includes a third delay element that delays the third amplified signal to generate a third delayed signal. A fourth driver amplifies the third delayed signal using a fourth gain to generate a fourth amplified signal. The summing circuit adds the fourth amplified signal to the sum.
In other features, the first, second and third delay elements provide at least one of unit delays and partial unit delays. The multiplexer receives L input lines at x frequency and outputs the first serial ATA signal at L*x frequency. L*x is greater than 1.4 GHz.
In other features, the first differential driver includes a gain control circuit that controls the first gain. n differential amplifiers have differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with the gain control circuit. The gain control circuit selectively enables the n differential amplifiers to adjust the first gain.
The second differential driver includes a pre-emphasis gain control circuit that controls the second gain. m differential amplifiers have differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with the pre-emphasis gain control circuit. The pre-emphasis gain control circuit selectively enables the m differential amplifiers to adjust the second gain.
In still other features, the communications channel has a band-limiting transmission characteristic. The pre-emphasis circuit compensates for the band-limiting transmission characteristic. The pre-emphasis circuit adjusts delays of the first and second delay elements and the first and second gains based on a selected communication channel medium.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1A is a functional block diagram of a host and a device with a connection based on the SATA standard according to the prior art;
FIG. 1B is a functional block diagram of a disk controller (host) and a disk drive (device) with a connection based on the SATA standard according to the prior art;
FIG. 1C is a functional block diagram of a serial ATA physical layer according to the prior art;
FIG. 2 is a functional block diagram of a differential driving device for the transmitter of the host and/or the device according to the prior art;
FIG. 3 illustrates a differential voltage waveform at the receiver end of an ideal communications channel;
FIG. 4 illustrates a differential voltage waveform at the receiver end of a band-limited communications channel;
FIG. 5 illustrates a closing “eye”-shaped waveform as the band limiting characteristics of a communications channel increase;
FIG. 6 is a functional block diagram of a transmitter with programmable pre-emphasis according to the present invention for a serial ATA channel;
FIG. 7 illustrates a transmission characteristic of a band-limited channel before pre-emphasis, an exemplary pre-emphasis transmission characteristic, and a transmission characteristic after pre-emphasis;
FIG. 8 is a functional block diagram of the transmitter of FIG. 6 in further detail;
FIGS. 9A-9C are waveforms for multi-clocking;
FIG. 10 is a functional block diagram of exemplary driving devices with programmable gain; and
FIG. 11 is a functional block diagram of one of the driving devices of FIG. 10.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements.
Referring now to FIG. 6, a transmitter 100 with programmable pre-emphasis according to the present invention for a serial ATA channel is shown. Data is received by a multiplexer 104 on L lines each at x MHz. For example, current serial ATA standards specify L=10 and x=150 MHz, although other numbers of input lines and higher or lower data rates are contemplated. The multiplexer 104 outputs data at L*x MHz. The transmitter 100 provides programmable pre-emphasis based on transmission characteristics of the communications channel 46 to reduce receiver error rates. For example, the transmitter 100 may provide pre-emphasis to offset band-limiting characteristics of the communications channel 46. Because the pre-emphasis is programmable, the transmitter 100 can be readily adapted to the particular transmission characteristics of other communications channels 46.
Referring now to FIG. 7, a transmission characteristic of a band-limited channel before pre-emphasis is shown generally at 120. A pre-emphasis transmission characteristic is shown at 124. The resulting or combined signal is shown at 128. As a result of the pre-emphasis in this example, the eye-shaped waveform 48 in FIG. 5 is opened, which improves data error rates of the receiver at the opposite end of the communications channel 46. As can be appreciated, the transmission characteristic and the pre-emphasis will vary for other types of communications channels 46.
Referring now to FIG. 8, the transmitter 100 includes driving devices 130-1, 130-2, 130-3, 130-4, . . . , and 130-n, delay elements 134-1, 134-2, 134-3, . . . , and 134-n, summing circuits 138-1, 138-2, 138-3, . . . , and 138-n, and a pre-emphasis gain control circuit 140. The data output by the multiplexer 104 is input to the driving device 130-1, which provides a first gain a0, and to a delay chain including the delay elements 134-1, 134-2, . . . , and 134-n. 
An output of the delay element 134-1 is input to the driving device 130-2, which provides a second gain a1. The output of the delay element 134-1 is also output to the delay element 134-2. An output of the delay element 134-2 is input to the driving device 130-3, which provides a third gain a2. The output of the delay element 134-2 is also input to the delay element 134-3. An output of the delay element 134-3 is input to the driving device 130-4, which provides a fourth gain a3. The output of the delay element 134-3 is also input to the delay element 134-n. An output of the delay element 134-n is input to the driving device 130-n, which provides a gain an.
Outputs of the driving device 130-n and the driving device 130-4 are input to the summer 138-4. Outputs of the driving device 130-3 and the summer 138-4 are input to the summer 138-3. Outputs of the driving device 130-2 and the summer 138-3 are input to the summer 138-2. Outputs of the driving device 130-1 and the summer 138-2 are input to the summer 138-1. An output of the summer 138-1 is transmitted over the communications channel 46 to the receiver at the opposite end of the communications channel 46. While two-input summing circuits 134-1, 134-2, 134-3, . . . , and 134-n are shown, summing circuits with three or more inputs can also be used to reduce the number of summing circuits 134.
While the circuit shown in FIG. 8 includes a primary stage 142 and three or more pre-emphasis stages 144-1, 144-2, 144-3 . . . , and 144-n (generally identified 144), the transmitter 100 can include the primary stage 142 and one or more pre-emphasis stages 144. The number of pre-emphasis stages 144 that are used for a particular design will depend on the accuracy of the impulse response that is desired and the desired cost of the circuit. Increasing the number of pre-emphasis stages 133 generally increases the cost of the transmitter 100.
The transmitter 100 that is shown in FIG. 8 implements the transfer function set forth below:

Output=a0+a1z−1+a2z−2+ . . . +anz−n 

While the foregoing example illustrates terms with unit delay elements, fractional delay elements can also be used. Referring now to FIGS. 9A-9C, using multi-clocking, the terms can be delayed for partial periods, such as T/2, T/3, . . . , or T/N. An example with three pre-emphasis terms and partial periods is as follows:

Output=a0+a1z−1/2+a2z−1+a3z−3/2 

In addition, the pre-emphasis stages 144 can be limited to odd delays, even delays or any other combination using additional delay elements. For example,

Output=a0+a1z−1+a3z−3+a5z−5 

The gains a0, a1, a2, . . . , and an can be positive, zero or negative, and not limited to integer values. Still other variations will be apparent to skilled artisans.

Referring now to FIGS. 10 and 11, an exemplary transmitter 100 is shown and includes main and pre-emphasis stages 142 and 144, respectively. Data D(0) is input to a main driving device 164-1 which provides the first gain a0. Delayed data D(1), D(2), . . . , and D(n) are input to driving devices 204-2, 204-3, . . . , 204-n, respectively, having the gains a1, a2, . . . , and an, respectively. The pre-emphasis gain control circuit 140 adjusts the gain of the data D(0) and the delayed data D(1), D(2), . . . and D(n) to provide a desired transmission characteristic. The desired transmission characteristics of various different media can be determined in advanced and stored in the pre-emphasis gain control circuit 140. Dip adjusts and/or software adjusts can be used to select the gain settings and delays for the particular medium being used.
Referring now to FIG. 11, one of the driving devices 204 is illustrated in further detail. Each driving device 164 includes one or more differential amplifiers 220-1, 220-2, 220-3, . . . , 220-m having inputs coupled to input lines IN+ and IN− and outputs coupled to output lines OUT+ and OUT−. The driving devices 204 of the transmitter 100 may have different numbers of differential amplifiers 220 as needed. The pre-emphasis gain control circuit 210 increases or decreases gain by enabling or disabling one or more differential amplifiers 220.
By providing programmable pre-emphasis, the transmitter 100 works with media having different transmission characteristics. With pre-emphasis, the transmitter provides compensation for degradation that occurs during transmission over the communications channel to reduce receiver error rates.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.

## Claims

1. A high-speed serial ATA physical layer that transmits data over a communications medium using a serial ATA protocol, comprising:
a serial ATA control circuit that controls operation of said serial ATA physical layer;
a serial ATA multiplexer that has a plurality of input lines for receiving input data, that has a control input that communicates with said serial ATA control circuit, and that outputs a serial ATA signal; and
a serial ATA analog front end that includes a first differential driver that communicates with said serial ATA multiplexer and that provides a first gain to said serial ATA signal and a serial ATA pre-emphasis circuit that provides pre-emphasis to said serial ATA signal to alter a transmission characteristic of said serial ATA signal.

2. The high-speed serial ATA physical layer of claim 1 wherein said serial ATA physical layer is implemented in at least one of a serial ATA device and a serial ATA host.

3. The high-speed serial ATA physical layer of claim 1 wherein said first differential driver generates a first amplified signal and wherein said pre-emphasis circuit includes a first delay element that delays said serial ATA signal to generate a first delayed signal, a second driver that amplifies said first delayed signal using a second gain to generate a second amplified signal, and a first summing circuit that adds said first amplified signal and said second amplified signal to generate a sum.

4. The high-speed serial ATA physical layer of claim 3 wherein said pre-emphasis circuit further includes:
a second delay element that delays said second amplified signal to generate a second delayed signal; and
a third driver that amplifies said second delayed signal using a third gain to generate a third amplified signal, wherein said summing circuit adds said third amplified signal to said sum.

5. The high-speed serial ATA physical layer of claim 4 wherein said pre-emphasis circuit further includes:
a third delay element that delays said third amplified signal to generate a third delayed signal; and
a fourth driver that amplifies said third delayed signal using a fourth gain to generate a fourth amplified signal, wherein said summing circuit adds said fourth amplified signal to said sum.

6. The high-speed serial ATA physical layer of claim 5 wherein said first, second and third delay elements provide at least one of a unit delay and a partial unit delay.

7. The high-speed serial ATA physical layer of claim 1 wherein said multiplexer receives L input lines at x frequency and outputs said first serial ATA signal at L*x frequency, and wherein L*x is greater than 1.4 GHz.

8. The high-speed serial ATA physical layer of claim 1 wherein said first differential driver includes:
a gain control circuit that controls said first gain; and
n differential amplifiers having differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with said gain control circuit, wherein said gain control circuit selectively enables said n differential amplifiers to adjust said first gain.

9. The high-speed serial ATA physical layer of claim 3 wherein said second differential driver includes:
a pre-emphasis gain control circuit that controls said second gain; and
m differential amplifiers having differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with said pre-emphasis gain control circuit, wherein said pre-emphasis gain control circuit selectively enables said m differential amplifiers to adjust said second gain.

10. The high-speed serial ATA physical layer of claim 1 wherein said communications channel has a band-limiting transmission characteristic and wherein said pre-emphasis circuit compensates for said band-limiting transmission characteristic.

11. The high-speed serial ATA physical layer of claim 3 wherein said pre-emphasis circuit adjusts delays of said first and second delay elements based on the communication channel medium.

12. The high-speed serial ATA physical layer of claim 3 wherein said pre-emphasis circuit adjusts said first and second gains based on the communication channel medium.

13. The high-speed serial ATA physical layer of claim 1 wherein said pre-emphasis is programmable.

14. The high-speed serial ATA physical layer of claim 13 wherein said pre-emphasis circuit is programmed using at least one of data stored in memory and data input to said serial ATA physical layer.

15. The high-speed serial ATA physical layer of claim 1 wherein said pre-emphasis circuit compensates for transmission characteristics of the communications medium.

16. A high-speed serial ATA physical layer that transmits data over a communications medium using a serial ATA protocol, comprising:
serial ATA control means for controlling operation of said serial ATA physical layer;
serial ATA multiplexing means for generating a serial ATA signal and having a plurality of input lines for receiving input data and a control input that communicates with said serial ATA control means; and
a serial ATA analog front end that includes first differential driving means that communicates with said serial ATA multiplexing means for providing a first gain to said serial ATA signal and serial ATA pre-emphasis means for providing pre-emphasis to said serial ATA signal to alter a transmission characteristic of said serial ATA signal.

17. The high-speed serial ATA physical layer of claim 16 wherein said serial ATA physical layer is implemented in at least one of a serial ATA device and a serial ATA host.

18. The high-speed serial ATA physical layer of claim 16 wherein said first differential driving means generates a first amplified signal, and wherein said pre-emphasis means includes a first delay means for delaying said serial ATA signal to generate a first delayed signal, second differential driving means for amplifying said first delayed signal using a second gain to generate a second amplified signal, and first summing means for adding said first amplified signal and said second amplified signal to generate a sum.

19. The high-speed serial ATA physical layer of claim 18 wherein said pre-emphasis means further includes:
second delay means for delaying said second amplified signal to generate a second delayed signal; and
third differential driving means for amplifying said second delayed signal using a third gain to generate a third amplified signal, wherein said summing means adds said third amplified signal to said sum.

20. The high-speed serial ATA physical layer of claim 19 wherein said pre-emphasis means further includes:
third delay means for delaying said third amplified signal to generate a third delayed signal; and
fourth differential driving means for amplifying said third delayed signal using a fourth gain to generate a fourth amplified signal, wherein said summing means adds said fourth amplified signal to said sum.

21. The high-speed serial ATA physical layer of claim 20 wherein said first, second and third delay means provide at least one of a unit delay and a partial unit delay.

22. The high-speed serial ATA physical layer of claim 16 wherein said multiplexing means receives L input lines at x frequency and outputs said first differential signal at L*x frequency, and wherein L*x is greater than 1.4 GHz.

23. The high-speed serial ATA physical layer of claim 16 wherein said first differential driving means includes:
gain control means for controlling said first gain; and
n differential amplifiers having differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with said gain control means, wherein said gain control means selectively enables said n differential amplifiers to adjust said first gain.

24. The high-speed serial ATA physical layer of claim 18 wherein said second differential driving means includes:
pre-emphasis gain control means for controlling said second gain; and
m differential amplifiers having differential inputs that communicate with first and second inputs, differential outputs that communicate with first and second outputs, and enable inputs that communicate with said pre-emphasis gain control means, wherein said pre-emphasis gain control means selectively enables said m differential amplifiers to adjust said second gain.

25. The high-speed serial ATA physical layer of claim 16 wherein said communications channel has a band-limiting transmission characteristic and wherein said pre-emphasis means compensates for said band-limiting transmission characteristic.

26. The high-speed serial ATA physical layer of claim 18 wherein said pre-emphasis means adjusts delays of said first and second delay means based on a selected communication channel medium.

27. The high-speed serial ATA physical layer of claim 18 wherein said pre-emphasis means adjusts said first and second gain based on a selected communication channel medium.

28. The high-speed serial ATA physical layer of claim 16 wherein said pre-emphasis is programmable.

29. The high-speed serial ATA physical layer of claim 28 wherein said pre-emphasis means is programmed using at least one of data stored in memory and data input to said serial ATA physical layer.

30. The high-speed serial ATA physical layer of claim 16 wherein said pre-emphasis means compensates for transmission characteristics of the communications medium.

31. A method for operating a high-speed serial ATA physical layer that transmits data over a communications medium using a serial ATA protocol, comprising:
controlling operation of said serial ATA physical layer;
generating a serial ATA signal from parallel input data; and
providing a first gain to said serial ATA signal; and
providing pre-emphasis to said serial ATA signal to alter a transmission characteristic of said serial ATA signal.

32. The method of claim 31 wherein said serial ATA physical layer is implemented in at least one of a serial ATA device and a serial ATA host.

33. The method of claim 31 further comprising:
amplifying said serial ATA signal using said first gain to generate a first amplified signal;
delaying said serial ATA signal to generate a first delayed signal;
amplifying said first delayed signal using a second gain to generate a second amplified signal; and
adding said first amplified signal and said second amplified signal to generate a sum.

34. The method of claim 33 further comprising:
delaying said second amplified signal to generate a second delayed signal;
amplifying said second delayed signal using a third gain to generate a third amplified signal; and
adding said third amplified signal to said sum.

35. The method of claim 34 wherein said pre-emphasis further includes:
delaying said third amplified signal to generate a third delayed signal;
amplifying said third delayed signal using a fourth gain to generate a fourth amplified signal; and
adding said fourth amplified signal to said sum.

36. The method of claim 35 further comprising provide at least one of a unit delay and a partial unit delay.

37. The method of claim 31 further comprising selectively enabling n differential amplifiers to adjust said first gain.

38. The method of claim 33 selectively enabling m differential amplifiers to adjust said second gain.

39. The method of claim 31 wherein said communications channel has a band-limiting transmission characteristic and wherein said pre-emphasis compensates for said band-limiting transmission characteristic.

40. The method of claim 33 wherein said pre-emphasis adjusts delays of said first and second delayed signals based on a selected communication channel medium.

41. The method of claim 33 wherein said pre-emphasis adjusts said first and second gains based on a selected communication channel medium.

42. The method of claim 31 wherein said pre-emphasis is programmable.

43. The method of claim 42 wherein said pre-emphasis is programmed using at least one of data stored in memory and data input to said serial ATA physical layer.

44. The method of claim 31 wherein said pre-emphasis compensates for transmission characteristics of the communications medium.

45. The high-speed serial ATA physical layer of claim 1 wherein said serial ATA pre-emphasis circuit adjusts gain of delayed signals that are generated based on said serial ATA signal to alter a transmission characteristic of said serial ATA signal.

46. The high-speed serial ATA physical layer of claim 1 wherein serial ATA pre-emphasis circuit provides said pre-emphasis based on a channel transmission characteristic.

47. The high-speed serial ATA physical layer of claim 1 wherein said pre-emphasis is preprogrammed.