
Data Sheet
February 1997
ATT3000 Series Field-Programmable Gate Arrays
Lucent Technologies Inc.
29
Performance
Device Performance
The high performance of the FPGA is due in part to the 
manufacturing process, which is similar to that used for 
high-speed CMOS static memories. Performance can 
be measured in terms of minimum propagation times 
for logic elements. The parameter which traditionally 
describes the overall performance of a gate array is the 
toggle frequency of a flip-flop. The configuration for 
determining the toggle performance of the FPGA is 
shown in Figure 26. The flip-flop output Q is fed back 
through the combinatorial logic as Q to form the toggle 
flip-flop.
Figure 26. Toggle Flip-Flop
FPGA performance is determined by the timing of 
critical paths, including both the fixed timing for the 
logic and storage elements in that path, and the timing 
associated with the routing of the network. Examples 
of internal worst-case timing are included in the 
performance data to allow the user to make the best 
use of the capabilities of the device. The 
ORCA
Foundry Development System timing calculator or 
ORCA
 Foundry-generated simulation models should 
be used to calculate worst-case paths by using actual 
impedance and loading information. 
Figure 27 shows a variety of elements which are 
involved in determining system performance. Table 20 
gives the parameter values for the different speed 
grades. Actual measurement of internal timing is not 
practical, and often only the sum of component 
timing is relevant as in the case of input to output. The 
relationship between input and output timing is arbi-
trary, and only the total determines performance. 
Timing components of internal functions may be deter-
mined by the measurement of differences at the pins of 
the package. A synchronous logic function which 
involves a clock to block-output and a block-input to 
clock setup is capable of higher-speed operation than a 
logic configuration of two synchronous blocks with an 
extra combinatorial block level between them. System 
clock rates to 60% of the toggle frequency are practical 
for logic in which an extra combinatorial level is located 
between synchronized blocks. This allows implementa-
tion of functions of up to 25 variables. The use of the 
wired-AND is also available for wide, high-speed 
functions. 
CLOCK
D Q
5-3117(F)
Figure 27. Examples of Primary Block Speed Factors 
CLOCK
LOGIC
LOGIC
CLB
CLB
CLB
(K)
(K)
IOB
PAD
T
CKO
T
ILO
T
ICK
T
 OP
CLOCK TO
OUTPUT
COMBINATORIAL
SETUP
IOB
T
PID
T
 OKOP
T
CKO
PAD
5-3118(F)