Reverse engineering old chips Ken Shirriff

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Current mirror “Clone” a current. More compact, accurate than resistors. I want to talk a bit about current mirrors since they are very common on analog <strong>chips</strong>. You may have seen the current source on datasheets and wondered what a current source is. Suppose you need a fixed current, for a bias, for a pullup, or for other circuits. You can resistors to control these currents. When you’re building a circuit, resistors are cheap and transistors are expensive. But on an IC, it’s the other way around. So instead of using a bunch of resistors, you use current mirrors. You set one current with a resistor. Then you can use transistors configured like this to mirror the current. So the current on the right is the same as the current on the left.
More info: righto.com/741 If we look at the 741, there are lots of current mirrors. There’s one big resistor up here that sets the current. And then current mirrors to copy that current precisely.
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Reverse engineering old chips Ken S
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Z80 (1976) Brq Wait Bak Wr Rd Irq M
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Instruction decoding PLA Instructio
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MOS transistors Drain Gate Source
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NAND gate +5 +5 Out 0 Out 1 1 Input
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NAND gate +5 Inputs Output Transist
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Gates get weird in the ALU +5 Out 4
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Sinclair Scientific Calculator (197
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Can see bits in the 320-word instru
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Intel shift-register memory (1970)
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More info: righto.com/shift
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Collector Collector Base Base Emitt
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What bipolar transistors really loo
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PNP transistor
Page 29 and 30: Interactive chip viewer More info:
Page 31: 741 op amp
Page 34 and 35: More info: righto.com/741
Page 36 and 37: 7805 voltage regulator 7-25V in 5V
Page 38 and 39: A family of regulators from one chi
Page 40 and 41: Stitch photos together for high-res
Page 42 and 43: Motorola 6820 PIA chip
Page 44 and 45: Easy way: download die photos zepto
Page 46 and 47: Current project: 8008 analysis
Page 48 and 49: Reverse engineering old chips Ken S
Page 50 and 51: Z80 (1976) Brq Wait Bak Wr Rd Irq M
Page 52 and 53: Instruction decoding PLA Instructio
Page 54 and 55: MOS transistors Drain Gate Source T
Page 56 and 57: NAND gate +5 +5 1 Inputs 1 Out 0 0
Page 58 and 59: NAND gate +5 Inputs Output Transist
Page 60 and 61: Gates get weird in the ALU +5 Out 4
Page 62 and 63: Sinclair Scientific Calculator (197
Page 64 and 65: Can see bits in the 320-word instru
Page 66 and 67: Intel shift-register memory (1970)
Page 68 and 69: More info: righto.com/shift Here’
Page 70 and 71: Collector Collector Base Base Emitt
Page 72 and 73: What bipolar transistors really loo
Page 74 and 75: PNP transistor PNP transistors are
Page 76 and 77: Interactive chip viewer More info:
Page 78 and 79: 741 op amp On the die you can see t
Page 82 and 83: Unusual current mirror transistors
Page 84 and 85: Vin Gnd Vsense Vout Here’s my die
Page 86 and 87: Die photos: Metallurgical microscop
Page 88 and 89: Hugin takes some practice Tip: have
Page 90 and 91: How to get to the die? Photo: zepto
Page 92 and 93: Acid-free way: chips without epoxy
Page 94: Blog: righto.com ken.shirriff@gmail
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Reverse engineering old chips Ken Shirriff

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