Does the Microchip/SMSC PHYBoost technology help with Rx, or does it boost Tx only?
$begingroup$
So I'm doing some configurations on a product which has a LAN9514 chip (datasheet), that features the "PHYBoost" technology.
Microchip's website is very vague about the technology, and my impression, after reading the datasheet, is that this feature will only increase the amplitude of the signals sent by the hub.
So my question is: Does it do anything for the signals which the hub is receiving?
usb microchip usb-hub
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
$endgroup$
add a comment |
$begingroup$
So I'm doing some configurations on a product which has a LAN9514 chip (datasheet), that features the "PHYBoost" technology.
Microchip's website is very vague about the technology, and my impression, after reading the datasheet, is that this feature will only increase the amplitude of the signals sent by the hub.
So my question is: Does it do anything for the signals which the hub is receiving?
usb microchip usb-hub
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
$endgroup$
add a comment |
$begingroup$
So I'm doing some configurations on a product which has a LAN9514 chip (datasheet), that features the "PHYBoost" technology.
Microchip's website is very vague about the technology, and my impression, after reading the datasheet, is that this feature will only increase the amplitude of the signals sent by the hub.
So my question is: Does it do anything for the signals which the hub is receiving?
usb microchip usb-hub
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
$endgroup$
So I'm doing some configurations on a product which has a LAN9514 chip (datasheet), that features the "PHYBoost" technology.
Microchip's website is very vague about the technology, and my impression, after reading the datasheet, is that this feature will only increase the amplitude of the signals sent by the hub.
So my question is: Does it do anything for the signals which the hub is receiving?
usb microchip usb-hub
usb microchip usb-hub
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
asked Jan 24 at 16:02
AndrejaKoAndrejaKo
17k2087166
17k2087166
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
From the datasheet, the only reference I can see to PHYBoost is:
PHYBoost which enables four programmable levels of USB signal drive strength in USB port transceivers
That indicates that basically it is controlling the drive strength of the transcievers. Drive strength is a property of transmit only, not receive.
More generally, from the link you posted to the technology brief, "PHYBoost" is basically appears to be just increasing the output voltage of the eye to try to compensate for signal attenuation.
For some background:
Badly designed transmission lines and connectors cause impedance mismatches and signal reflections that basically distort the "eye" of the signal being transmitted (basically changes the rise and fall times, as well as the peak voltages). If the eye is distorted too much, the receiver will no longer be able to confidently determine whether a 1 or a 0 was sent, causing an increse in the bit error rate.
There is very little you can do about this at the receiver end. In some systems you can overcome this using oversampling and filtering or equalisation techniques. However these are not supported by the part in question - as such once the signal is distorted to the point where it violates the eye requirements of the receiver, the information is already lost.
Fortunately, the distortion from reflections and frequency dispertion cauused by transmission line effects is fairly constant for a given system (that is it doesn't vary much over time). Because of this, it can be possible to improve the eye by changing the shape of the transmit signals. You basically predistort the signal in a way that once passed through the transmission line gets distorted back into the correct shape.
Some systems like PCIe have training mechanisms to determine what if any distortion (pre-emphasis, de-emphasis) of the signals can assist. Other systems have non-standard (IC specific) ways of the ability to do some distortion based on configuration settings.
On further inspection it seems that the PHYBoost isn't doing any clever predistortion, it's just increasing the differential voltage of the transmitters.
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
$endgroup$
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
|
show 5 more comments
$begingroup$
this feature will only increase the amplitude of the signals sent by
the hub.
Yes, this is unconditionally correct. The "boost" settings just increase the current drive source by 4-8-12%. The reason is also clearly spelled out:
"PHYBoost attempts to restore USB signal integrity that has been compromised by system level variables such as poor PCB layout, long cables, etc."
In other words, if your design is inside a big-big enclosure, and if your budget constraints prevent you from bringing the hub ICs in close proximity to user-accessible ports (using some small daughter sub-boards) and you have to use long cables inside the enclosure to reach external ports, the signal amplitude at the point of measuring (and therefore during USB-IF certification process) will be decreased by natural causes, no matter how well do you match impedance etc. The PHYBoost feature was designed to accommodate this kind of designs and make them certifiable. The boost doesn't do any "pre-emphasis", although Intel does it for the same reasons (big motherboards with thin convoluted traces need some boost).
Does it do anything for the signals which the hub is receiving?
Unfortunately, no. The so-called "USB receiver sensitivity" is a different and challenging matter. The USB specifies a fairly narrow range of squelch threshold (100 mV) and full no-error receiving above 150 mV, with grey area between 100 and 150 mV. If the environment is noisy (and long wires do not improve that), it might be a challenge to meet the certification requirement. AFAIK, MCHP/SMSC has no means to control these thresholds, unfortunately.
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
$endgroup$
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
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active
oldest
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active
oldest
votes
$begingroup$
From the datasheet, the only reference I can see to PHYBoost is:
PHYBoost which enables four programmable levels of USB signal drive strength in USB port transceivers
That indicates that basically it is controlling the drive strength of the transcievers. Drive strength is a property of transmit only, not receive.
More generally, from the link you posted to the technology brief, "PHYBoost" is basically appears to be just increasing the output voltage of the eye to try to compensate for signal attenuation.
For some background:
Badly designed transmission lines and connectors cause impedance mismatches and signal reflections that basically distort the "eye" of the signal being transmitted (basically changes the rise and fall times, as well as the peak voltages). If the eye is distorted too much, the receiver will no longer be able to confidently determine whether a 1 or a 0 was sent, causing an increse in the bit error rate.
There is very little you can do about this at the receiver end. In some systems you can overcome this using oversampling and filtering or equalisation techniques. However these are not supported by the part in question - as such once the signal is distorted to the point where it violates the eye requirements of the receiver, the information is already lost.
Fortunately, the distortion from reflections and frequency dispertion cauused by transmission line effects is fairly constant for a given system (that is it doesn't vary much over time). Because of this, it can be possible to improve the eye by changing the shape of the transmit signals. You basically predistort the signal in a way that once passed through the transmission line gets distorted back into the correct shape.
Some systems like PCIe have training mechanisms to determine what if any distortion (pre-emphasis, de-emphasis) of the signals can assist. Other systems have non-standard (IC specific) ways of the ability to do some distortion based on configuration settings.
On further inspection it seems that the PHYBoost isn't doing any clever predistortion, it's just increasing the differential voltage of the transmitters.
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
$endgroup$
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
|
show 5 more comments
$begingroup$
From the datasheet, the only reference I can see to PHYBoost is:
PHYBoost which enables four programmable levels of USB signal drive strength in USB port transceivers
That indicates that basically it is controlling the drive strength of the transcievers. Drive strength is a property of transmit only, not receive.
More generally, from the link you posted to the technology brief, "PHYBoost" is basically appears to be just increasing the output voltage of the eye to try to compensate for signal attenuation.
For some background:
Badly designed transmission lines and connectors cause impedance mismatches and signal reflections that basically distort the "eye" of the signal being transmitted (basically changes the rise and fall times, as well as the peak voltages). If the eye is distorted too much, the receiver will no longer be able to confidently determine whether a 1 or a 0 was sent, causing an increse in the bit error rate.
There is very little you can do about this at the receiver end. In some systems you can overcome this using oversampling and filtering or equalisation techniques. However these are not supported by the part in question - as such once the signal is distorted to the point where it violates the eye requirements of the receiver, the information is already lost.
Fortunately, the distortion from reflections and frequency dispertion cauused by transmission line effects is fairly constant for a given system (that is it doesn't vary much over time). Because of this, it can be possible to improve the eye by changing the shape of the transmit signals. You basically predistort the signal in a way that once passed through the transmission line gets distorted back into the correct shape.
Some systems like PCIe have training mechanisms to determine what if any distortion (pre-emphasis, de-emphasis) of the signals can assist. Other systems have non-standard (IC specific) ways of the ability to do some distortion based on configuration settings.
On further inspection it seems that the PHYBoost isn't doing any clever predistortion, it's just increasing the differential voltage of the transmitters.
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
$endgroup$
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
|
show 5 more comments
$begingroup$
From the datasheet, the only reference I can see to PHYBoost is:
PHYBoost which enables four programmable levels of USB signal drive strength in USB port transceivers
That indicates that basically it is controlling the drive strength of the transcievers. Drive strength is a property of transmit only, not receive.
More generally, from the link you posted to the technology brief, "PHYBoost" is basically appears to be just increasing the output voltage of the eye to try to compensate for signal attenuation.
For some background:
Badly designed transmission lines and connectors cause impedance mismatches and signal reflections that basically distort the "eye" of the signal being transmitted (basically changes the rise and fall times, as well as the peak voltages). If the eye is distorted too much, the receiver will no longer be able to confidently determine whether a 1 or a 0 was sent, causing an increse in the bit error rate.
There is very little you can do about this at the receiver end. In some systems you can overcome this using oversampling and filtering or equalisation techniques. However these are not supported by the part in question - as such once the signal is distorted to the point where it violates the eye requirements of the receiver, the information is already lost.
Fortunately, the distortion from reflections and frequency dispertion cauused by transmission line effects is fairly constant for a given system (that is it doesn't vary much over time). Because of this, it can be possible to improve the eye by changing the shape of the transmit signals. You basically predistort the signal in a way that once passed through the transmission line gets distorted back into the correct shape.
Some systems like PCIe have training mechanisms to determine what if any distortion (pre-emphasis, de-emphasis) of the signals can assist. Other systems have non-standard (IC specific) ways of the ability to do some distortion based on configuration settings.
On further inspection it seems that the PHYBoost isn't doing any clever predistortion, it's just increasing the differential voltage of the transmitters.
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
$endgroup$
From the datasheet, the only reference I can see to PHYBoost is:
PHYBoost which enables four programmable levels of USB signal drive strength in USB port transceivers
That indicates that basically it is controlling the drive strength of the transcievers. Drive strength is a property of transmit only, not receive.
More generally, from the link you posted to the technology brief, "PHYBoost" is basically appears to be just increasing the output voltage of the eye to try to compensate for signal attenuation.
For some background:
Badly designed transmission lines and connectors cause impedance mismatches and signal reflections that basically distort the "eye" of the signal being transmitted (basically changes the rise and fall times, as well as the peak voltages). If the eye is distorted too much, the receiver will no longer be able to confidently determine whether a 1 or a 0 was sent, causing an increse in the bit error rate.
There is very little you can do about this at the receiver end. In some systems you can overcome this using oversampling and filtering or equalisation techniques. However these are not supported by the part in question - as such once the signal is distorted to the point where it violates the eye requirements of the receiver, the information is already lost.
Fortunately, the distortion from reflections and frequency dispertion cauused by transmission line effects is fairly constant for a given system (that is it doesn't vary much over time). Because of this, it can be possible to improve the eye by changing the shape of the transmit signals. You basically predistort the signal in a way that once passed through the transmission line gets distorted back into the correct shape.
Some systems like PCIe have training mechanisms to determine what if any distortion (pre-emphasis, de-emphasis) of the signals can assist. Other systems have non-standard (IC specific) ways of the ability to do some distortion based on configuration settings.
On further inspection it seems that the PHYBoost isn't doing any clever predistortion, it's just increasing the differential voltage of the transmitters.
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
edited Jan 24 at 23:58
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
answered Jan 24 at 16:27
Tom CarpenterTom Carpenter
39.5k372119
39.5k372119
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
|
show 5 more comments
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
2
2
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
Actually, you can do something on the receive side: equalization. Both continuous time and decision feedback (DFE) equalization at the receiver can compensate for some amount of high frequency loss, reflections, etc.
$endgroup$
– alex.forencich
Jan 24 at 23:20
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
@alex.forencich receive side equalisation requires oversampling the input doesn't it?
$endgroup$
– Tom Carpenter
Jan 24 at 23:43
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
Equalization requires channel training using special pattern sequences. USB 2.0 doesn't define and doesn't have any pre-de-emphasis nor CTLE and any training mechanisms, so discussing them in the context of this particular question is moot.
$endgroup$
– Ale..chenski
Jan 24 at 23:53
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
$begingroup$
More than 1 quantization level or even an ADC, but it's usually only one sample per symbol.
$endgroup$
– alex.forencich
Jan 24 at 23:55
1
1
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
$begingroup$
Equalization doesn't require training sequences. CTLE is just an analog filter of sorts, and DFE can adapt in the background while the link is in normal use. Adjusting pre-emphasis levels usually does require special training sequences, though.
$endgroup$
– alex.forencich
Jan 25 at 0:08
|
show 5 more comments
$begingroup$
this feature will only increase the amplitude of the signals sent by
the hub.
Yes, this is unconditionally correct. The "boost" settings just increase the current drive source by 4-8-12%. The reason is also clearly spelled out:
"PHYBoost attempts to restore USB signal integrity that has been compromised by system level variables such as poor PCB layout, long cables, etc."
In other words, if your design is inside a big-big enclosure, and if your budget constraints prevent you from bringing the hub ICs in close proximity to user-accessible ports (using some small daughter sub-boards) and you have to use long cables inside the enclosure to reach external ports, the signal amplitude at the point of measuring (and therefore during USB-IF certification process) will be decreased by natural causes, no matter how well do you match impedance etc. The PHYBoost feature was designed to accommodate this kind of designs and make them certifiable. The boost doesn't do any "pre-emphasis", although Intel does it for the same reasons (big motherboards with thin convoluted traces need some boost).
Does it do anything for the signals which the hub is receiving?
Unfortunately, no. The so-called "USB receiver sensitivity" is a different and challenging matter. The USB specifies a fairly narrow range of squelch threshold (100 mV) and full no-error receiving above 150 mV, with grey area between 100 and 150 mV. If the environment is noisy (and long wires do not improve that), it might be a challenge to meet the certification requirement. AFAIK, MCHP/SMSC has no means to control these thresholds, unfortunately.
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
$endgroup$
add a comment |
$begingroup$
this feature will only increase the amplitude of the signals sent by
the hub.
Yes, this is unconditionally correct. The "boost" settings just increase the current drive source by 4-8-12%. The reason is also clearly spelled out:
"PHYBoost attempts to restore USB signal integrity that has been compromised by system level variables such as poor PCB layout, long cables, etc."
In other words, if your design is inside a big-big enclosure, and if your budget constraints prevent you from bringing the hub ICs in close proximity to user-accessible ports (using some small daughter sub-boards) and you have to use long cables inside the enclosure to reach external ports, the signal amplitude at the point of measuring (and therefore during USB-IF certification process) will be decreased by natural causes, no matter how well do you match impedance etc. The PHYBoost feature was designed to accommodate this kind of designs and make them certifiable. The boost doesn't do any "pre-emphasis", although Intel does it for the same reasons (big motherboards with thin convoluted traces need some boost).
Does it do anything for the signals which the hub is receiving?
Unfortunately, no. The so-called "USB receiver sensitivity" is a different and challenging matter. The USB specifies a fairly narrow range of squelch threshold (100 mV) and full no-error receiving above 150 mV, with grey area between 100 and 150 mV. If the environment is noisy (and long wires do not improve that), it might be a challenge to meet the certification requirement. AFAIK, MCHP/SMSC has no means to control these thresholds, unfortunately.
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
$endgroup$
add a comment |
$begingroup$
this feature will only increase the amplitude of the signals sent by
the hub.
Yes, this is unconditionally correct. The "boost" settings just increase the current drive source by 4-8-12%. The reason is also clearly spelled out:
"PHYBoost attempts to restore USB signal integrity that has been compromised by system level variables such as poor PCB layout, long cables, etc."
In other words, if your design is inside a big-big enclosure, and if your budget constraints prevent you from bringing the hub ICs in close proximity to user-accessible ports (using some small daughter sub-boards) and you have to use long cables inside the enclosure to reach external ports, the signal amplitude at the point of measuring (and therefore during USB-IF certification process) will be decreased by natural causes, no matter how well do you match impedance etc. The PHYBoost feature was designed to accommodate this kind of designs and make them certifiable. The boost doesn't do any "pre-emphasis", although Intel does it for the same reasons (big motherboards with thin convoluted traces need some boost).
Does it do anything for the signals which the hub is receiving?
Unfortunately, no. The so-called "USB receiver sensitivity" is a different and challenging matter. The USB specifies a fairly narrow range of squelch threshold (100 mV) and full no-error receiving above 150 mV, with grey area between 100 and 150 mV. If the environment is noisy (and long wires do not improve that), it might be a challenge to meet the certification requirement. AFAIK, MCHP/SMSC has no means to control these thresholds, unfortunately.
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
$endgroup$
this feature will only increase the amplitude of the signals sent by
the hub.
Yes, this is unconditionally correct. The "boost" settings just increase the current drive source by 4-8-12%. The reason is also clearly spelled out:
"PHYBoost attempts to restore USB signal integrity that has been compromised by system level variables such as poor PCB layout, long cables, etc."
In other words, if your design is inside a big-big enclosure, and if your budget constraints prevent you from bringing the hub ICs in close proximity to user-accessible ports (using some small daughter sub-boards) and you have to use long cables inside the enclosure to reach external ports, the signal amplitude at the point of measuring (and therefore during USB-IF certification process) will be decreased by natural causes, no matter how well do you match impedance etc. The PHYBoost feature was designed to accommodate this kind of designs and make them certifiable. The boost doesn't do any "pre-emphasis", although Intel does it for the same reasons (big motherboards with thin convoluted traces need some boost).
Does it do anything for the signals which the hub is receiving?
Unfortunately, no. The so-called "USB receiver sensitivity" is a different and challenging matter. The USB specifies a fairly narrow range of squelch threshold (100 mV) and full no-error receiving above 150 mV, with grey area between 100 and 150 mV. If the environment is noisy (and long wires do not improve that), it might be a challenge to meet the certification requirement. AFAIK, MCHP/SMSC has no means to control these thresholds, unfortunately.
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
answered Jan 24 at 21:05
Ale..chenskiAle..chenski
28.1k11866
28.1k11866
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