673:) drivers have a strong pull-down strength but a weaker pull-up strength. The purpose is to reduce the overall power demand compared to using both a strong pull-up and a strong pull-down. A pure open-drain driver, by comparison, has no pull-up strength except for leakage current: all the pull-up action is on the external termination resistor. This is why the term "pseudo" has to be used here: there is some pull-up on the driver side when output is at high state, the remaining pull-up strength is provided by parallel-terminating the receiver at the far end to the high voltage, often using a switchable, on-die terminator instead of a separate resistor.
530:
443:
659:
211:
124:
501:
to interface different families of devices that have different operating voltage levels. The open collector transistor can be rated to withstand a higher voltage than the chip supply voltage. This technique is commonly used by logic circuits operating at 5 V or lower to drive higher voltage devices such as
500:
Because the pull-up resistor is external and does not need to be connected to the chip supply voltage, a lower or higher voltage than the chip supply voltage can be used instead (provided it does not exceed the absolute maximum rating of the chip's output). Open outputs are therefore sometimes used
559:
Another advantage is that more than one open-collector output can be connected to a single line. If all open collector outputs attached to a line are off (i.e. in the high-impedance state), the pull-up resistor will be the only device setting the line's voltage and will pull the line voltage high.
560:
But if one or more open-collector outputs attached to the line are on (i.e. conducting to ground), since any one of them are strong enough to overcome the pull-up resistor's limited ability to hold the voltage high, the line voltage will instead be pulled low. This
575:. The output will be high (true) only when all gates are in the high-impedance state, and will be low (false) otherwise, like Boolean AND. When treated as active-low logic, this behaves like Boolean OR, since the output is low (true) when any input is low. See
638:
One problem such open-collector and similar devices with a pull-up resistor is the resistor consumes power constantly while the output is low. Higher operating speeds require lower resistor values for faster pull-up, which consume even more power.
115:) have greater conductance than their PNP and pMOS relatives, so may be more commonly used for these outputs. Open outputs using PNP and pMOS transistors will use the opposite internal voltage rail used by NPN and nMOS transistors.
607:
was mistakenly used instead, the active device attempting to set the line voltage low would be in competition with the other devices attempting to set the line voltage high, which would result in unpredictable output and heat.
738:
logic states, as well as a control to turn off both transistors to isolate the output. This differs from open collector/drain output, which only use a single transistor that can only disconnect the output or connect it to
702:) for the input is not half-supply as was in DDR3 and may be higher. A comparison of both DDR3 and DDR4 termination schemes in terms of skew, eye aperture and power consumption was published in late 2011.
243:
Microelectronic devices using nMOS open drain output may provide a 'weak' (high-resistance, often on the order of 100 kΩ) internal pull-up resistor to connect the terminal in question to the positive
325:
For a pMOS open source output, the drain is internally connected to the low voltage rail, so the output instead connects to the low voltage rail when the transistor is on, or is hi-Z when off.
478:⎏ – NPN open emitter or similar output that can supply a relatively low-impedance high voltage when not turned off. Requires external pulldown. Capable of positive-logic wired-OR connection.
466:⎐ – NPN open collector or similar output that can supply a relatively low-impedance low voltage when not turned off. Requires external pullup. Capable of positive-logic wired-AND connection.
240:(undefined) because the MOSFET is not conducting, which is why nMOS open drain outputs require a pull-up resistor connected to a positive voltage rail for producing a high output voltage.
65:
typically connects to another terminal of that transistor. When the transistor is off, the output is internally disconnected from any internal power rail, a state called "high-impedance" (
214:
nMOS open drain output is pulled Low when the nMOS is conducting. In the nonconducting hi-Z state, an external resistor pulls the output High so the output's voltage does not float.
322:
For a nMOS open source output, the drain is internally connected to the positive voltage rail, so the source outputs a high voltage when the transistor is on and is hi-Z when off.
308:
For pMOS open drain, the output instead connects to the positive power rail when the transistor is on, and is hi-Z when off. This is sometimes called "open drain, drives high".
202:
For a PNP open emitter output, the collector is connected to the low voltage supply, so the emitter outputs a low voltage when the transistor is on and is hi-Z when off.
281:
286:
and possibly avoid the need for an external pull-up. External pullups may be 'stronger' (lower resistance, perhaps 3 kΩ) to reduce signal rise times (like with
1009:
Addenddum No. 6 to JESD8 – High Speed
Transceiver Logic (HSTL) – A 1.5 V Output Buffer Supply Voltage Based Interface Standard for Digital Integrated Circuits
698:). The term POD in DDR4 referring only for termination type that is only parallel pull-up without the pull-down termination at the far end. The reference point (V
849:
880:
96:
are typically required to set the output during the Hi-Z state to a specific voltage. Analog applications include analog weighting, summing, limiting, and
679:
standardized the terms POD15, POD125, POD135, and POD12 for 1.5 V, 1.25 V, 1.35 V, and 1.2 V interface supply voltages respectively.
154:
For NPN open collector outputs, the emitter of the NPN transistor is internally connected to ground, so the NPN open collector internally forms either a
112:
969:
181:, so the collector outputs a high voltage when the transistor is on or is hi-Z when off. This is sometimes called "open collector, drives high".
761:
576:
815:
603:). Open-collector output enables one active device to drive the shared line without interference from the other inactive devices. If
545:
will pull the output high. But if any input is low, the output will be pulled low by the buffer for that input. This corresponds to
1104:
1068:
643:
990:
135:
transistor, which controls the transistor's switching to the IC's ground. The external output is the transistor's collector.
1249:
567:
By tying the output of several open collectors together and connecting to a pull-up resistor, the common line becomes a
549:
AND in active-high logic, or to wired OR in active-low logic, and allows multiple inputs to share the same output wire.
17:
839:
248:
of the device so their output voltage doesn't float. Such weak pullups reduce power consumption due to their lower
1221:
1191:
870:
777:
492:
Note: this section primarily deals with npn open collectors, however nMOS open drain generally applies as well.
1215:
61:
with an exposed terminal that is internally unconnected (i.e. "open"). One of the IC's internal high or low
1244:
1097:
627:
97:
177:
For PNP open collector outputs, the emitter of the PNP transistor is internally connected to the positive
144:
108:
84:
These open outputs configurations are often used for digital applications when the transistor acts as a
1209:
1179:
961:
514:
1280:
1203:
1139:
642:
Also when driving a load, current through the pull-up resistor reduces the output high voltage by a
1090:
561:
554:
546:
305:, the strength of the internal pull-up, and allow disabling internal pullups when not desired.
89:
54:
174:, which pulls the output voltage to the resistor's supply voltage when the transistor is off.
163:
1197:
1151:
529:
251:
236:
when a low voltage is applied to the gate. The voltage in this high impedance state would be
1032:
1044:
1020:
721:
690:
uses POD12 drivers but with the same driver strength (34 Ω/48 Ω) for pull-down (R
604:
302:
159:
70:
1056:
1008:
802:
8:
245:
199:, so the emitter outputs a high voltage when the transistor is on and is hi-Z when off.
1227:
229:
148:
128:
50:
46:
572:
442:
170:
or "hi-Z") when the transistor is off. The output is usually connected to an external
909:
731:
715:
588:
158:(technically low impedance or "low-Z") connection to the low voltage (which could be
506:
1259:
711:
626:
Open collector outputs can also be useful for analog weighting, summing, limiting,
542:
534:
470:
298:
171:
93:
78:
614:-1 devices use open collector for electrical signaling. SCSI-2 and SCSI-3 may use
481:⎑ – variant with an internal pull-down resistor to provide a low voltage when off.
994:
931:
592:
502:
658:
901:
538:
447:
233:
167:
104:
1274:
283:
210:
155:
1254:
1113:
647:
196:
195:
For an NPN open emitter output, the collector is connected to the positive
178:
62:
301:
may allow programming particular output pins to use open drain instead of
1174:
1134:
1129:
687:
518:
455:
58:
1069:
Pseudo-open drain and Center-tab termination type termination schemes
123:
1082:
615:
74:
932:"Overview of IEEE Standard 91-1984 Explanation of Logic Symbols"
1157:
1121:
902:"SNx407 and SNx417 Hex Buffers and Drivers With Open-Collector"
600:
222:
85:
596:
287:
875:
844:
803:"Influence of Pin Setting on System Function and Performance"
676:
577:
Transistor–transistor logic § Open collector wired logic
510:
427:
Configurations that internally connect to a high voltage are
431:
Configurations that internally connect to a low voltage are
131:'s internal function is applied as the base input for a NPN
1145:
611:
459:
225:
instead of BJTs, and expose the MOSFET's drain as output.
66:
759:
810:
147:(BJT), whose collector is exposed as the external output
143:
processes an IC's output through the base of an internal
132:
734:: Consists of transistors to source and sink current in
724:: Consists of transistors to source and sink current in
755:
753:
73:, which use a pair of transistors to output a specific
630:, etc., but such applications are not discussed here.
127:
NPN open collector output schematic. A signal from an
254:
750:
646:
equal to the current times resistance, according to
228:
An nMOS open drain output connects to ground when a
537:. If all inputs are high, each buffer will be in a
275:
113:metal oxide semiconductor field effect transistor
1272:
69:). Open outputs configurations thus differ from
27:Transistor switch output for integrated circuits
232:is applied to the MOSFET's gate, or presents a
53:configurations that process the IC's internal
1098:
718:: Used more for analog voltages than digital.
533:Four inputs are connected to open-collector
328:
1045:POD135 – 1.35 V Pseudo Open Drain Interface
766:(2nd ed.). Cambridge University Press.
319:exposes the MOSFET's source as the output.
1105:
1091:
653:
1228:Current mode logic / Source-coupled logic
1057:POD12 – 1.2 V Pseudo Open Drain Interface
1021:POD15 – 1.5 V Pseudo Open Drain Interface
991:"Overview of SCSI Standards & Cables"
662:Pseudo open drain usage in DDR interfaces
495:
334:Summary of different open configurations
657:
528:
441:
209:
122:
800:
290:) or to minimize noise (like on system
88:, to allow for logic-level conversion,
14:
1273:
1086:
959:
760:Paul Horowitz; Winfield Hill (1989).
716:common terminal transistor amplifiers
364:HIGH voltage connected to collector
840:"source driver, (current-) | JEDEC"
473:to provide a high voltage when off.
437:
402:LOW voltage connected to collector
345:internal voltage supply connection
192:exposes the emitter as the output.
24:
1112:
394:HIGH voltage connected to emitter
166:, or an open-circuit (technically
25:
1292:
1078:
871:"sink driver, (current-) | JEDEC"
413:HIGH voltage connected to source
356:LOW voltage connected to emitter
118:
962:"Basics: Open Collector Outputs"
633:
521:requiring more than 100 V.
383:HIGH voltage connected to drain
375:LOW voltage connected to source
1192:Direct-coupled transistor logic
1062:
1050:
1038:
1026:
1014:
1002:
972:from the original on 2022-12-20
883:from the original on 2023-09-05
852:from the original on 2023-09-05
821:from the original on 2022-10-23
582:
487:
421:LOW voltage connected to drain
184:
983:
953:
924:
894:
863:
832:
794:
770:
524:
311:
13:
1:
960:Oskay, Windell (2012-02-29).
778:"open-emitter output | JEDEC"
743:
682:
205:
92:, and line sharing. External
628:digital-to-analog converters
454:Open output is indicated on
98:digital-to-analog converters
7:
1222:Transistor–transistor logic
1033:Pseudo Open Drain Interface
728:logic states, not just one.
705:
515:vacuum fluorescent displays
145:bipolar junction transistor
109:bipolar junction transistor
10:
1297:
1210:Integrated injection logic
552:
469:⎒ – variant with internal
450:with open-collector output
1237:
1216:Resistor–transistor logic
1204:Gunning transceiver logic
1167:
1140:Depletion-load NMOS logic
1120:
621:
587:Line sharing is used for
406:
387:
368:
349:
329:Summary of configurations
162:) when the transistor is
654:Pseudo open drain (POD)
446:Schematic symbol for a
276:{\displaystyle V^{2}/R}
223:MOS transistor (MOSFET)
90:wired-logic connections
1180:Diode–transistor logic
801:Kotzian, Jiri (2015).
763:The Art of Electronics
663:
562:wired logic connection
555:Wired logic connection
550:
496:Logic-level conversion
451:
277:
215:
136:
94:pull-up/down resistors
1198:Emitter-coupled logic
1152:Pass transistor logic
661:
532:
445:
278:
213:
141:open collector output
126:
252:
335:
190:Open emitter output
111:) and nMOS (n-type
1168:Other technologies
966:Evil Mad Scientist
664:
564:has several uses.
551:
452:
333:
317:Open source output
273:
216:
137:
47:integrated circuit
1268:
1267:
1146:Complementary MOS
1035:(September 2017).
999:081214 scsita.org
939:Texas Instruments
910:Texas Instruments
732:Three-state logic
667:Pseudo open drain
573:active high logic
425:
424:
342:exposed terminal
219:Open drain output
71:push–pull outputs
18:Pseudo open drain
16:(Redirected from
1288:
1281:Digital circuits
1260:Four-phase logic
1142:(including HMOS)
1107:
1100:
1093:
1084:
1083:
1072:
1066:
1060:
1054:
1048:
1042:
1036:
1030:
1024:
1018:
1012:
1006:
1000:
998:
993:. Archived from
987:
981:
980:
978:
977:
957:
951:
950:
948:
946:
936:
928:
922:
921:
919:
918:
906:
898:
892:
891:
889:
888:
867:
861:
860:
858:
857:
836:
830:
829:
827:
826:
820:
807:
798:
792:
791:
789:
788:
774:
768:
767:
757:
722:Push–pull output
712:Common collector
694:) and pull-up (R
605:push–pull output
543:pull-up resistor
471:pull-up resistor
438:Schematic symbol
336:
332:
303:push–pull output
299:microcontrollers
293:
282:
280:
279:
274:
269:
264:
263:
172:pull-up resistor
21:
1296:
1295:
1291:
1290:
1289:
1287:
1286:
1285:
1271:
1270:
1269:
1264:
1233:
1163:
1116:
1111:
1081:
1076:
1075:
1067:
1063:
1055:
1051:
1043:
1039:
1031:
1027:
1023:(October 2009).
1019:
1015:
1007:
1003:
989:
988:
984:
975:
973:
958:
954:
944:
942:
934:
930:
929:
925:
916:
914:
904:
900:
899:
895:
886:
884:
869:
868:
864:
855:
853:
838:
837:
833:
824:
822:
818:
805:
799:
795:
786:
784:
776:
775:
771:
758:
751:
746:
708:
701:
697:
693:
685:
656:
636:
624:
585:
557:
527:
503:electric motors
498:
490:
440:
429:source drivers.
391:open collector
353:open collector
331:
314:
291:
265:
259:
255:
253:
250:
249:
208:
187:
121:
28:
23:
22:
15:
12:
11:
5:
1294:
1284:
1283:
1266:
1265:
1263:
1262:
1257:
1252:
1247:
1241:
1239:
1235:
1234:
1232:
1231:
1225:
1219:
1213:
1207:
1201:
1195:
1189:
1186:Open collector
1183:
1177:
1171:
1169:
1165:
1164:
1162:
1161:
1155:
1149:
1143:
1137:
1132:
1126:
1124:
1122:MOS technology
1118:
1117:
1114:Logic families
1110:
1109:
1102:
1095:
1087:
1080:
1079:External links
1077:
1074:
1073:
1061:
1059:(August 2011).
1049:
1037:
1025:
1013:
1011:(August 1995).
1001:
997:on 2008-12-10.
982:
952:
923:
893:
862:
831:
793:
769:
748:
747:
745:
742:
741:
740:
729:
719:
707:
704:
699:
695:
691:
684:
681:
655:
652:
635:
632:
623:
620:
584:
581:
553:Main article:
541:state and the
539:high-impedance
526:
523:
507:LEDs in series
497:
494:
489:
486:
485:
484:
483:
482:
476:
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439:
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327:
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272:
268:
262:
258:
234:high impedance
207:
204:
186:
183:
168:high impedance
120:
119:Open collector
117:
31:Open collector
26:
9:
6:
4:
3:
2:
1293:
1282:
1279:
1278:
1276:
1261:
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1199:
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1190:
1187:
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1166:
1159:
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1144:
1141:
1138:
1136:
1133:
1131:
1128:
1127:
1125:
1123:
1119:
1115:
1108:
1103:
1101:
1096:
1094:
1089:
1088:
1085:
1070:
1065:
1058:
1053:
1047:(March 2018).
1046:
1041:
1034:
1029:
1022:
1017:
1010:
1005:
996:
992:
986:
971:
967:
963:
956:
940:
933:
927:
912:
911:
903:
897:
882:
878:
877:
872:
866:
851:
847:
846:
841:
835:
817:
813:
812:
804:
797:
783:
782:www.jedec.org
779:
773:
765:
764:
756:
754:
749:
737:
733:
730:
727:
723:
720:
717:
713:
710:
709:
703:
689:
680:
678:
674:
672:
668:
660:
651:
649:
645:
640:
634:Disadvantages
631:
629:
619:
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613:
609:
606:
602:
598:
594:
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574:
570:
565:
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540:
536:
531:
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520:
516:
512:
508:
504:
493:
480:
479:
477:
472:
468:
467:
465:
464:
463:
461:
457:
449:
444:
435:
434:
433:sink drivers.
430:
420:
417:
416:
412:
409:
405:
401:
399:open emitter
398:
397:
393:
390:
386:
382:
379:
378:
374:
371:
367:
363:
361:open emitter
360:
359:
355:
352:
348:
344:
341:
338:
337:
326:
323:
320:
318:
309:
306:
304:
300:
295:
289:
285:
284:ohmic heating
270:
266:
260:
256:
247:
241:
239:
235:
231:
226:
224:
220:
212:
203:
200:
198:
193:
191:
182:
180:
175:
173:
169:
165:
161:
157:
156:short-circuit
152:
150:
146:
142:
134:
130:
125:
116:
114:
110:
106:
101:
99:
95:
91:
87:
82:
80:
76:
72:
68:
64:
63:voltage rails
60:
56:
52:
48:
44:
40:
36:
32:
19:
1255:Domino logic
1185:
1158:Bipolar–CMOS
1064:
1052:
1040:
1028:
1016:
1004:
995:the original
985:
974:. Retrieved
965:
955:
945:February 12,
943:. Retrieved
938:
926:
915:. Retrieved
908:
896:
885:. Retrieved
874:
865:
854:. Retrieved
843:
834:
823:. Retrieved
809:
796:
785:. Retrieved
781:
772:
762:
735:
725:
686:
675:
670:
666:
665:
644:voltage drop
641:
637:
625:
610:
586:
583:Line sharing
568:
566:
558:
513:, 50 V
509:, 12 V
499:
491:
488:Applications
453:
432:
428:
426:
418:open source
380:open source
324:
321:
316:
315:
307:
296:
246:power supply
242:
237:
230:high voltage
227:
218:
217:
201:
197:voltage rail
194:
189:
188:
185:Open emitter
179:voltage rail
176:
153:
140:
138:
102:
83:
49:(IC) output
42:
39:open emitter
38:
34:
30:
29:
1175:Diode logic
688:DDR4 memory
525:Wired logic
519:Nixie tubes
458:with these
410:open drain
372:open drain
339:transistor
312:Open source
164:switched on
43:open source
1135:NMOS logic
1130:PMOS logic
976:2023-01-15
917:2023-01-18
887:2023-09-06
856:2023-09-06
825:2022-12-27
787:2023-06-27
744:References
714:and other
683:DDR memory
589:interrupts
456:schematics
206:Open drain
59:transistor
57:through a
35:open drain
1230:(CML/SCL)
648:Ohm's law
595:(such as
569:wired AND
462:symbols:
294:inputs).
45:refer to
1275:Category
1160:(BiCMOS)
970:Archived
881:Archived
850:Archived
816:Archived
706:See also
238:floating
107:(n-type
55:function
1250:Dynamic
739:ground.
616:EIA-485
535:buffers
297:Modern
105:NPN BJT
79:current
75:voltage
1245:Static
1194:(DCTL)
1148:(CMOS)
941:. 1996
913:. 1983
622:Analog
601:1-Wire
511:relays
448:buffer
160:ground
86:switch
41:, and
1238:Types
1224:(TTL)
1218:(RTL)
1206:(GTL)
1200:(ECL)
1182:(DTL)
1154:(PTL)
935:(PDF)
905:(PDF)
876:JEDEC
845:JEDEC
819:(PDF)
806:(PDF)
677:JEDEC
593:buses
547:wired
517:, or
407:pMOS
369:nMOS
292:RESET
221:uses
1212:(IL)
1188:(OC)
947:2020
736:both
726:both
696:onPu
692:onPd
612:SCSI
591:and
460:IEEE
388:PNP
350:NPN
103:The
67:Hi-Z
811:NXP
700:REF
671:POD
599:or
597:I²C
571:in
288:I²C
149:pin
139:An
133:BJT
77:or
51:pin
1277::
968:.
964:.
937:.
907:.
879:.
873:.
848:.
842:.
814:.
808:.
780:.
752:^
650:.
618:.
579:.
505:,
151:.
129:IC
100:.
81:.
37:,
33:,
1106:e
1099:t
1092:v
1071:.
979:.
949:.
920:.
890:.
859:.
828:.
790:.
669:(
271:R
267:/
261:2
257:V
20:)
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