Glue Logic
Logic Speed x Power Chart

Logic Family Power Dissipation

Speed vs Power Chart
IC Propagation Speed vs Power Dissipation

This is a graph of Glue Logic speed [in nS] vs. Quiescent power consumption [in mW]. The switching speed is constant as defined in the graph, but the power consumption will change as the device switches. Quiescent means the device is in a steady state, at rest or not being used. While the device is stopped the graph holds true for power consumption, but as the device starts to operate the current increases. So as the switching speed increases many of the CMOS logic family devices will approach the TTL logic family devices for power consumption. It only holds when the devices are not operating! CMOS logic families consume little power because their output pin resides between one NMOS FET and one PMOS FET, so normally only one FET is conducting. How ever as the device begins to switch both FETs begin to conduct increasing the current consumption of the device. As the CMOS current consumption increases it begins to approach the consumption of TTL devices. Seems like I saw by 50Khz the CMOS and TTL families consumed the same power, may have been 500KHz. In either case the slope of the consumption curve is different, as the TTL devices increase their current consumption faster then the CMOS devices. But by 50KHz they both level out at about the same current demand. The ECL [Emitter Coupled Logic] devices consume the same current regardless of the switching speed.
The X axis represents Quiescent power consumption (mW), the lower the number the less power used. The graph shows the glue logic families with no input signal applied. When switching, CMOS and TTL dissipate near the same power.
The Y axis represents propagation delay in 'nS' [10-9 seconds], the lower the number the faster the device.

This is a guide, the numbers change with each different company. I believe that I picked an average number to represent the family. Complied back in 1995, I think I used Propagation delay numbers for AND gates (which are normally available in all families). All TTL, CMOS, mixed TTL/CMOS and ECL Glue Logic families are listed. So based on this graph the best Glue Logic IC family to use would be ACTQ; Advanced CMOS with TTL input logic switching levels, with non-spike-ing outputs [slow output switching levels]. There are a number of bus driver families which are not listed above. Bus driver families normally only contain 'bus' drivers and receivers.

In general a CMOS logic family should always be used over a TTL logic family.
CMOS gates only dissipate power when the internal gates are switching, while TTL gates draw current continuously.
If TTL interfacing is required, use a CMOS logic family with a T in the part number, indicating that the CMOS gate will switch at TTL levels.
This sub-family of parts only shift the voltage levels [TTL Switching Levels], an ACT part, for example, is still an advanced CMOS device.

Back to Designing with Logic for additional IC hints.
For a listing of Glue Logic vendors, see the glue logic IC manufacturers page.
For any other IC manufacturer, see the Components icon below. Related engineering topic; Logic Design Derating Factor.

Editor Note: Virtually all of these device families are still in production, although many should be avoided.

Topic Navigation: Engineering Home > Design Guides > IC Application Notes > IC Power Loss vs. Glue Logic Family.

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Modified: 2/2/12
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