Last Edit July 22, 2001
The Macros and Their Options
For the bipolar arrays and for the interface portion of the BiCMOS arrays,
macro selection plays a major role in the final power dissipated by the
Macros that are fast, have high fan-out drive capability or are dense
(read chip-efficient) are high-current macros. The macro library should
be reviewed for the existence of options or versions. A macro library
may have low-power versions or options of its macros. (Note: AMCC CMOS
macros have no options.)
Once the design is blocked and the macros selected, the timing requirements
should be reviewed and the macros adjusted by option when options are
available and can be applied.
As discussed during the chapter on timing, low-power macros are slower
than the standard or high-speed options. Low-power macros may have a lower
fan-out load limit. Low-power macros may have a lower maximum frequency
of operation and narrower minimum pulse width. None of these variations
are absolute, i.e., they vary with the array.
Macro Option Examples
The AMCC Q5000 Bipolar Series macro library has options for most of its
internal macros and many of its interface macros.
- The low-power L-option macros have a lower drive (4 versus 9 loads)
and are slower than the standard S-option macros they can replace.
- High-speed H-option macros have the same drive as the S-option macros
but are faster and use more current.
- Driver macros (macros with a high fan-out limit) have no options.
- The super-driver macros (with a 25 load limit) average approximately
5 mA of worst-case current versus the 2.5 mA average current of the
15-load driver macros.
The AMCC Q20000 Bipolar Series macro library also contains L-, S-, and
H- options. In this series, all options have the same fan-out load limit,
a function of the Turbo output feature. What is different is that some
H-options use more cells than the L-and S-options. All other considerations
of differences between the options remain the same.
Design Rules for Macro Options
- Always review a library to determine:
- if it has options or versions of its macros,
- which macros do and don't have options or versions,
- what macros are similar with minor variants to other macros, and
- the different limitations on the applicability of the options,
versions and variants.
- During design and when available, H-option macros, high fan-out drivers
and other high-current macros should be used judiciously to avoid
unnecessary high current - high power dissipation.
- The use of L-option macros when available can help balance the use
of high-current macros providing speed - power programmability if
and only if the minimum pulse widths are not violated.
- Select macro options and versions carefully! Double-check time and
power impacts of your choices.
Power-Down and Conditional Geometry - Bipolar
If a bipolar macro library is implemented with conditional geometry,
macro outputs that are not used (are terminated) have their IOEF
current sources shut-down. Only one version of the macro needs to be supplied
in these libraries. Note that not all macros in the library allow this
Terminated Outputs - Bipolar
When power-down is not allowed, the macros in the bipolar library may
be available in different versions. For example three macros may perform
the same function with one supplying a non-inverted Y output, one supplying
an inverted YN output and one supplying both Y and YN. The macro version
selected should reflect output usage.
One or two macros that are not a perfect match may not be a problem in
the design but dozens of terminated yet powered-up outputs can be expensive
because of the power supply and packaging options required by the higher-than-necessary
Terminated Outputs - BiCMOS, CMOS
CMOS and internal BiCMOS macros may have their power computation based on
the number of outputs switching (vendor-dependent equation). Both used and
terminated outputs are counted in the computation. Therefore, for BiCMOS
and CMOS arrays, the objective is to minimize the number of terminated outputs.
This objective is no different from the objective for bipolar arrays.
Inverted Outputs for Distortion Management
The need for signal inversion in high-speed paths for skew and pulse
distortion control may require YN (inverted output). However, there may
be a different speed associated with each of the output polarities. One
design objective is to maintain the timing considerations of both speed
and distortion management while managing power.
Power considerations require that macros exist in a library in different
versions to allow the flexibility of inversion with no additional cost
- The AMCC Q5000 Series macros feature power down for over 90% of the
- The AMCC Q14000 and Q24000 BiCMOS Series interface macros were not
implemented with conditional geometry.
- The AMCC Q20000 Series macros have no conditional geometry due to
use of a completely different process and technology.
- The BiCMOS and high-speed bipolar libraries supply different versions
of various macros to allow for optimum selection.