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LOG112 Log Amp LTspice symbol.

This is the result of my work mentioned in the previous thread, subject: 'Subcircuit levels', and LTspice...

The first post in that thread has the unedited LOG112 model from Texas Instruments. (Save it as LOG112.sub if you want it for LTspice, where it will work as it is).

I decided to make a full diagram (copied from the datasheet and slightly modified to save space) for the symbol to help me learn how to use the device. That might help others as much as me, so here's the whole symbol file. (Save as LOG112.asy for LTspice).

Version 4 SymbolType CELL LINE Normal 138 28 128 24 LINE Normal 118 36 138 28 LINE Normal 138 44 118 36 LINE Normal 118 52 138 44 LINE Normal 138 60 118 52 LINE Normal 118 68 138 60 LINE Normal 128 72 118 68 LINE Normal 64 -48 64 -96 LINE Normal -76 -56 -88 -80 LINE Normal -88 -56 -40 -56 LINE Normal -52 -56 -40 -80 LINE Normal -64 -56 -64 128 LINE Normal -40 -80 -16 -80 LINE Normal -79 -71 -88 -80 LINE Normal -86 -67 -88 -80 LINE Normal 36 16 36 32 LINE Normal 28 24 44 24 LINE Normal 28 -24 44 -24 LINE Normal 20 -32 -16 -32 LINE Normal 20 32 0 32 LINE Normal 108 0 128 0 LINE Normal 108 0 20 -51 LINE Normal 20 51 108 0 LINE Normal 20 -51 20 51 LINE Normal 84 138 88 128 LINE Normal 76 118 84 138 LINE Normal 68 138 76 118 LINE Normal 60 118 68 138 LINE Normal 52 138 60 118 LINE Normal 44 118 52 138 LINE Normal 40 128 44 118 LINE Normal 128 128 128 72 LINE Normal 88 128 128 128 LINE Normal 228 16 228 32 LINE Normal 220 24 236 24 LINE Normal 220 -24 236 -24 LINE Normal 212 -32 192 -32 LINE Normal 212 32 160 32 LINE Normal 300 0 320 0 LINE Normal 300 0 212 -51 LINE Normal 212 51 300 0 LINE Normal 212 -51 212 51 LINE Normal -148 -56 -136 -80 LINE Normal -136 -56 -184 -56 LINE Normal -172 -56 -184 -80 LINE Normal -160 -56 -160 96 LINE Normal -184 -80 -288 -80 LINE Normal -145 -71 -136 -80 LINE Normal -138 -67 -136 -80 LINE Normal -88 -80 -136 -80 LINE Normal -252 16 -252 32 LINE Normal -260 24 -244 24 LINE Normal -260 -24 -244 -24 LINE Normal -268 -32 -320 -32 LINE Normal -268 32 -288 32 LINE Normal -180 0 -112 0 LINE Normal -180 0 -268 -51 LINE Normal -268 51 -180 0 LINE Normal -268 -51 -268 51 LINE Normal -112 -80 -112 0 LINE Normal -288 -80 -288 -32 LINE Normal -16 -80 -16 64 LINE Normal -288 32 -288 80 LINE Normal 0 32 0 80 LINE Normal -288 80 0 80 LINE Normal -320 64 -16 64 LINE Normal -160 96 128 96 LINE Normal -64 128 40 128 LINE Normal -96 80 -96 160 LINE Normal 128 -96 128 -80 LINE Normal 192 -96 192 -32 LINE Normal 0 128 0 160 LINE Normal -224 128 -192 128 LINE Normal -320 128 -272 128 LINE Normal -192 128 -192 160 LINE Normal 128 24 128 -48 LINE Normal 128 -80 160 -80 LINE Normal 160 -80 160 32 LINE Normal 64 -48 128 -48 RECTANGLE Normal 320 160 -320 -96 RECTANGLE Normal -224 144 -272 112 CIRCLE Normal -286 -30 -290 -34 CIRCLE Normal -110 -78 -114 -82 CIRCLE Normal -94 82 -98 78 CIRCLE Normal -14 -30 -18 -34 CIRCLE Normal 2 130 -2 126 CIRCLE Normal 130 98 126 94 CIRCLE Normal 130 2 126 -2 TEXT 8 152 Left 0 GND TEXT 200 152 Left 0 V+ TEXT 264 152 Left 0 V- TEXT -88 152 Left 0 Vcm TEXT -184 152 Left 0 Vref GND TEXT -312 120 Left 0 Vref TEXT -312 56 Left 0 I2 TEXT -312 -40 Left 0 I1 TEXT 72 -88 Left 0 Vlog TEXT 136 -88 Left 0 +In TEXT 200 -88 Left 0 -In TEXT 295 -8 Left 0 Out TEXT 187 136 Left 0 Power Inputs WINDOW 0 -208 -112 Center 0 WINDOW 3 -96 32 Center 0 SYMATTR Value LOG112 SYMATTR Prefix X SYMATTR Description LOG112 Logarithmic Amplifier. SYMATTR ModelFile LOG112.sub PIN -320 -32 RIGHT 8 PINATTR SpiceOrder 1 PIN 128 -96 BOTTOM 8 PINATTR SpiceOrder 2 PIN 192 -96 BOTTOM 8 PINATTR SpiceOrder 3 PIN 64 -96 BOTTOM 8 PINATTR SpiceOrder 4 PIN 192 160 BOTTOM 8 PINATTR SpiceOrder 5 PIN 320 0 LEFT 8 PINATTR SpiceOrder 6 PIN -320 128 RIGHT 8 PINATTR SpiceOrder 7 PIN 256 160 BOTTOM 8 PINATTR SpiceOrder 8 PIN 0 160 TOP 8 PINATTR SpiceOrder 9 PIN -192 160 TOP 8 PINATTR SpiceOrder 10 PIN -96 160 TOP 8 PINATTR SpiceOrder 11 PIN -320 64 RIGHT 8 PINATTR SpiceOrder 12

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Lostgallifreyan
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A variant, more compact, and clearer for simple log converters like frequency to pitch converters in synthesisers. It makes it easier to place other symbols when 3 decades of dynamic range (about ten octaves worth) are enough. Feed about 100µA from Vref to I2, feed exponential voltage (proportional to frequency) into I2 via a resistor (100K for Vmax of 10V), put compensation capacitor between I2 and Vlog. The Vlog output is inverted so the standard inverting op-amp can be made to invert, scale, and offset using Vref or other voltage as offset source. it will all need tweaking and better understanding, but if anyone finds this while looking for a LTspice circuit for electronic music purposes, this could be a useful start. The LOG112 was the best way I could find to do what Bob Moog did, with none of that awkward temeperature compensation needed.

Version 4 SymbolType CELL LINE Normal 138 28 128 24 LINE Normal 118 36 138 28 LINE Normal 138 44 118 36 LINE Normal 118 52 138 44 LINE Normal 138 60 118 52 LINE Normal 118 68 138 60 LINE Normal 128 72 118 68 LINE Normal 64 -64 64 -96 LINE Normal -60 -56 -72 -80 LINE Normal -72 -56 -24 -56 LINE Normal -36 -56 -24 -80 LINE Normal -48 -56 -48 128 LINE Normal -24 -80 0 -80 LINE Normal -63 -71 -72 -80 LINE Normal -70 -67 -72 -80 LINE Normal 36 16 36 32 LINE Normal 28 24 44 24 LINE Normal 28 -24 44 -24 LINE Normal 20 -32 0 -32 LINE Normal 20 32 0 32 LINE Normal 108 0 128 0 LINE Normal 108 0 20 -51 LINE Normal 20 51 108 0 LINE Normal 20 -51 20 51 LINE Normal 84 138 88 128 LINE Normal 76 118 84 138 LINE Normal 68 138 76 118 LINE Normal 60 118 68 138 LINE Normal 52 138 60 118 LINE Normal 44 118 52 138 LINE Normal 40 128 44 118 LINE Normal 128 128 128 72 LINE Normal 88 128 128 128 LINE Normal 196 16 196 32 LINE Normal 188 24 204 24 LINE Normal 188 -24 204 -24 LINE Normal 180 -32 160 -32 LINE Normal 180 32 160 32 LINE Normal 268 0 288 0 LINE Normal 268 0 180 -51 LINE Normal 180 51 268 0 LINE Normal 180 -51 180 51 LINE Normal -132 -56 -120 -80 LINE Normal -120 -56 -168 -56 LINE Normal -156 -56 -168 -80 LINE Normal -144 -56 -144 96 LINE Normal -168 -80 -272 -80 LINE Normal -129 -71 -120 -80 LINE Normal -122 -67 -120 -80 LINE Normal -72 -80 -120 -80 LINE Normal -236 16 -236 32 LINE Normal -244 24 -228 24 LINE Normal -244 -24 -228 -24 LINE Normal -252 -32 -272 -32 LINE Normal -252 32 -272 32 LINE Normal -164 0 -96 0 LINE Normal -164 0 -252 -51 LINE Normal -252 51 -164 0 LINE Normal -252 -51 -252 51 LINE Normal -96 -80 -96 0 LINE Normal -272 -80 -272 -32 LINE Normal 0 -96 0 -32 LINE Normal -272 32 -272 80 LINE Normal 0 32 0 80 LINE Normal -272 80 0 80 LINE Normal -144 96 128 96 LINE Normal -48 128 40 128 LINE Normal -96 80 -96 160 LINE Normal 160 -96 160 -32 LINE Normal 0 128 0 160 LINE Normal -208 128 -192 128 LINE Normal -288 128 -240 128 LINE Normal -192 128 -192 160 LINE Normal 128 24 128 -64 LINE Normal 160 32 160 160 LINE Normal 64 -64 128 -64 LINE Normal -192 -96 -192 -80 RECTANGLE Normal 288 160 -288 -96 RECTANGLE Normal -208 144 -240 112 CIRCLE Normal -190 -78 -194 -82 CIRCLE Normal -94 -78 -98 -82 CIRCLE Normal -94 82 -98 78 CIRCLE Normal 2 -78 -2 -82 CIRCLE Normal 2 130 -2 126 CIRCLE Normal 130 98 126 94 CIRCLE Normal 130 2 126 -2 TEXT 8 152 Left 0 GND TEXT 264 64 Left 0 V+ TEXT 264 128 Left 0 V- TEXT -88 152 Left 0 Vcm TEXT -184 152 Left 0 Vref GND TEXT -280 120 Left 0 Vref TEXT 8 -88 Left 0 I2 TEXT -184 -88 Left 0 I1 TEXT 72 -88 Left 0 Vlog TEXT 168 152 Left 0 +In TEXT 168 -88 Left 0 -In TEXT 263 -8 Left 0 Out WINDOW 0 -96 -112 Center 0 WINDOW 3 -96 32 Center 0 SYMATTR Value LOG112 SYMATTR Prefix X SYMATTR Description LOG112 Logarithmic Amplifier. SYMATTR ModelFile LOG112.sub PIN -192 -96 RIGHT 8 PINATTR SpiceOrder 1 PIN 160 160 BOTTOM 8 PINATTR SpiceOrder 2 PIN 160 -96 BOTTOM 8 PINATTR SpiceOrder 3 PIN 64 -96 BOTTOM 8 PINATTR SpiceOrder 4 PIN 288 64 BOTTOM 8 PINATTR SpiceOrder 5 PIN 288 0 LEFT 8 PINATTR SpiceOrder 6 PIN -288 128 RIGHT 8 PINATTR SpiceOrder 7 PIN 288 128 BOTTOM 8 PINATTR SpiceOrder 8 PIN 0 160 TOP 8 PINATTR SpiceOrder 9 PIN -192 160 TOP 8 PINATTR SpiceOrder 10 PIN -96 160 TOP 8 PINATTR SpiceOrder 11 PIN 0 -96 RIGHT 8 PINATTR SpiceOrder 12

Reply to
Lostgallifreyan

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