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| — | quiz:3h7e0f4_io_data [2016/01/03 04:20] (current) – created mcmaster |
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| | ====== Inputs and outputs ====== |
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| | In the previous module you came up with the pin numbering scheme and identified power and ground. Now we'll go a little deeper to figure out data flow. |
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| | * Identify the circle containing ESD protection |
| | * Detail |
| | * {{:quiz:metal_gate_cmos:esd_q.jpg?600|}} |
| | - A |
| | - B |
| | - C |
| | - D |
| | - E |
| | * [1] |
| | * (1) |
| | * Many chips use large parallel diodes for ESD protection and so this ones a little different. However, ESD protection can often be identified by virtue of a component that attaches to both VDD and VSS. While some of the transistors do this, they have logical connections that indicate they have a higher purpose. ESD protection on the other hand tends to be very simple and regular. Looking at the components in A I believe they are resistors as seen with NMOS logic (ex: see Intel 4004 die photos and Flylogic analysis). Presumably this provides a more favorable conductive path and shunts away from the input gates. |
| | * B is a transistor |
| | * C is a transistor |
| | * D is a bond wire (ball bond) |
| | * E just has more metal and metal doesn't typically help ESD. It can on larger chips when its used as a capacitor between VDD and VSS |
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| | * Identify inputs |
| | * Detail |
| | * {{:quiz:metal_gate_cmos:iodir_q.jpg?600|}} |
| | * ie not outputs or power/ground |
| | - A |
| | - B |
| | - C |
| | - D |
| | - E |
| | * [1|4|5] |
| | * (1) |
| | * Anything with a fat transistor near the pad not connected to a gate is a pretty clear output or possibly tri-state. I highlighted a gate on each questioned input, although keep in mind that simply having a gate attached to a pin doesn't make it an input as the circuit can have feedback or tri-state (necessary but not sufficient). Going through each pin you see that each is either connected to only gates or only source/drain. We can now identify all pins as either power, input or output. D had to be traced to the other side of the die and is the lowest circled gate. |
| | * {{:quiz:metal_gate_cmos:iodir_a.jpg?600|}} |
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