Case Study: Sizing A Design
Last Edit July 22, 2001
SOLUTION - Q20000
Check for I/O mode and power supply.
This is a 100% ECL circuit and uses no Darlingtons so that a single -5.2V
supply is allowed.
The AMCC chip macro is Q20080ECL10K, which sets the I/O mode at 100%
ECL with ECL 10K/KH inputs. The power supply parameter is set at STD5
for standard reference -5.2V supply. The product grade parameter is set
at MIL for military. Between them, these parameters define this circuit
as a MIL5 circuit, using the MIL5 library and annotation data. The chip
macro is shown in Figure A-2.
Figure A-2 AMCC Icon for the Chip Macro
Selecting a flip/flop - first pass
The need for a master reset will reduce the set of available flip/flop
macros that could be used to those with a synchronous or asynchronous
reset (or set). The use of a 2:1 MUX - flip/flop combination will further
reduce the choices for the first stage of the circuit.
For the chosen Q20000 macro library, FF46S is a D flip/flop with a 2:1
MUX on the data input and an asynchronous reset. It is more silicon-efficient
to use a combination MUX-F/F macro than to implement the design with individual
multiplexor and flip/flop macros.
The second stage flip/flop needs a reset and at this stage in the design
process needs both Q and QN outputs. FF10S was chosen as the appropriate
macro. See Figure A-3.
Figure A-3 MUX and two F/Fs in Two Macros
Selecting the ECL input
All inputs (reset, selects, output enables and data) except the clock
will use the IE93S, a simple buffered input that produces both Y and YN
outputs shown in Figure A-4. The YN output will be used to input
to the gate tree to keep loading off the Y path. To reduce power, the
IE94 version with only the Y output could have been chosen. This option
would use three loads on the Y path, two to the main circuit (register
input and 16:1 MUX input) and one to the parametric tree.
Figure A-4 Output Macro with Complementary Outputs
For this circuit, the saving of one load is not significant in that the
loads are not in the critical path. In another instance, the reduction
of one load could be the difference between meeting or failing specification.
There are 64 data inputs, 32 dataA and 32 dataB, plus one select for
the input 2:1 MUX, and four for the 16:1 MUX controls (and four 16:1 MUXs)
for a total of 82 IE93S macros. Each macro uses one I/O cell and one pad.
(See Table A-1.)
Table A-1 Required IE93S Inputs
|32 data A
|32 data B
| 1 reset control
| 5 data MUX control select
| 2 output enables (MUX outputs)
| 6 pass-through inputs
|78 IE93S inputs