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T PHL and T PLH: why can they be different?

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elektroda.net NewsGroups Forum Index - Electronics Equipment - T PHL and T PLH: why can they be different?

Merciadri Luca
Guest

Tue Jan 11, 2011 4:54 pm   



Hi,

Consider the propagation time from H (high) to L (low): T PHL.
Consider the propagation time from L to H: T PLH. Why are they
generally different (in value)? Note that I'm not here speaking about
the propagation delay, T PD defined as max(T PHL, T PLH).

Thanks.

Phil Hobbs
Guest

Tue Jan 11, 2011 4:54 pm   



Merciadri Luca wrote:
Quote:
Hi,

Consider the propagation time from H (high) to L (low): T PHL.
Consider the propagation time from L to H: T PLH. Why are they
generally different (in value)? Note that I'm not here speaking about
the propagation delay, T PD defined as max(T PHL, T PLH).

Thanks.

Did you read anything about how the circuits work? Look for asymmetries
in the device properties and circuit topology.

Hint: the physics of PMOS and NMOS devices are not as similar as they
might seem.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

Merciadri Luca
Guest

Tue Jan 11, 2011 5:53 pm   



On Jan 11, 4:12 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
Quote:
Merciadri Luca wrote:
Hi,

Consider the propagation time from H (high) to L (low): T PHL.
Consider the propagation time from L to H: T PLH. Why are they
generally different (in value)? Note that I'm not here speaking about
the propagation delay, T PD defined as max(T PHL, T PLH).

Thanks.

Did you read anything about how the circuits work?  Look for asymmetries
in the device properties and circuit topology.

Hint: the physics of PMOS and NMOS devices are not as similar as they
might seem.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net

Thanks!

Rich Grise
Guest

Wed Jan 12, 2011 12:11 am   



Merciadri Luca wrote:
Quote:

Consider the propagation time from H (high) to L (low): T PHL.
Consider the propagation time from L to H: T PLH. Why are they
generally different (in value)? Note that I'm not here speaking about
the propagation delay, T PD defined as max(T PHL, T PLH).

Generally, because bipolar transistors aren't symmetrical, top to

bottom.

These days, with CMOS, that difference is being eroded.

Hope This Helps!
Rich

elektroda.net NewsGroups Forum Index - Electronics Equipment - T PHL and T PLH: why can they be different?

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