1、JEDEC STANDARD Measurement of Small Values of Transistor Capacitance JESD398 (Previously known as RS-398 and/or EIA-398) JULY 1972 (Reaffirmed: April 1981, April 1999, March 2009) JEDEC SOLID STATE TECHNOLOGY ASSOCIATION NOTICE JEDEC standards and publications contain material that has been prepared
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7、or call (703) 907-7559 or www.jedec.org Published by JEDEC Solid State Technology Association 2009 3103 North 10th Street Suite 240 South Arlington, VA 22201-2107 This document may be downloaded free of charge; however JEDEC retains the copyright on this material. By downloading this file the indivi
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10、22201-2107 or call (703) 907-7559 MAY 1972 EIA STANDARD f or MEASUREMENT OF SMALL VALUES OF TRANSISTOR CAPACITANCE ELECTRONIC INDUSTRIES ASSOCIATION STANDARD RS-398 Formulated by JEDEC Solid State Products Council NOTICE EIA engineering standards are designed to serve the public interest through eli
11、minating mis- understandings between manufacturers and purchasers, facilitating interchan eability and improve- ment of products, and assistin the purchaser in selectin .a . . and obtaining wit mnumum delay the pro clu i f er product for his particu ar need. Existence of sue 1 standards shall not in
12、 any respect pre- e any member or non-member of EIA from manufacturing or selling products not conformin these tubes to be imbedded in an insulating material suitable for the frequency of measurement. See Figure 1. The spacing of the guide tubes shall conform closely enough to the spacing of the tra
13、nsistors leads so that misalignment deformation will not prevent the transistor header from bottoming against the test socket. The guide tubes shall extend as close to the top surface of the socket as possible and still provide insulation from the transistor header but in no case shall be further th
14、an 1.6 millimeters from the reference plane. The guide tubes may or may not contain wiping type contacts, but if they do not, then the inner diameter of the tubes shall be small enough to ensure that electrical contact shall be made with the leads of the transistor. They shall be long enough to comp
15、letely contain the transistors lead wires when the transistor is pushed down firmly against the RS-398 - fw3 INSULATING LEAD GUIDE (IF USED1 SEATING PLANE INSULATING ALIGNMENT (CONNECT TO GUARD CIRCUIT) COAX CONNECTORS OR COAX CABLE FIGURE 1 - TRANSISTOR MOUNT -FOR MEASUREMENT OF SMALL-VALUE CAPACIT
16、ANCES test socket. In this manner the capacitance measurement will be independent of the length of the transistors leads. The transistors header shall be bottomed against the test socket during the measurement. The test socket shall be mounted in a metal panel and the bottom, or lead portion, of the
17、 socket shall be totally enclosed in a grounded metal container so as to reduce the effects of hand capacitance and stray fields. Provision shall be made for feeding the bias voltages and current through the shielding to the socket terminals. The wires connecting the bridge and the metering circuitr
18、y to the socket should be shielded. 1.3 Measurement Techniques These are small signal measurements. This signal level should be small enough that doubling or halving it will not appreciably change the measured capacitance values, at least within the accuracy of measurement. The dc bias should be app
19、lied so as not to affect the accuracy of the ac measurement. The measurement frequency shall be specified. Care should be taken that the frequency is low enough not to introduce error because of the inductance of the exposed leads, preferably less than 2MH.z. The bridge should be carefully balanced
20、according to the instructions of the bridge manufacturer. It is important that the ac signal between emitter and base, when one of these terminals is guarded, be kept low (zero, if possible) so as not to affect the accuracy of measurement. The guard terminal is connected to the shielding system and
21、the internal ac guard system which prevents stray capacitance from affecting the measurement. It is also desirable that the ac signal between base and collector be minimized in the Ccb measurement. Various pieces of commercial equipment differ as to the designation of the measurement terminal which
22、is nearest the ac potential of the guard terminal. For example, on some pieces of equipment the “high” terminal is close to the “guard” ac potential; on others, the “low” terminal is at “guard” ac potential. 1.4 Equivalent Circuits The generalized equivalent circuits of the four different case conne
23、ctions are shown in Figure 2. The interelectrode capacitances, the stray capacitances to case, and stray capacitances to ground make up the equivalent circuit. If the signal level is small enough, the device will behave as a passive rather than an active circuit. Accordingly, judicious use of the gu
24、ard circuit connection will allow isolation of capacitances in a manner not otherwise possible. 2. MEASUREMENTS 2.1 Ccb This measurement is made with the collector-base diode reverse biased (VCg must.be specified) and is defined for use here with the emitter dc open circuited (IF = 0) but ac connect
25、ed to the guard RS-388 Page 4 terminal. Referring to Figure 2, we define this capacitance as being Ccb (which for grounded element devices must include the extra case capacitance). 2.1.1 Circuit of Ccb Figure 3 shows the test hookup for the Ccb measurement. Note that the collector and base terminals
26、 are tied to the measurement terminals and the emitter is ac connected to the guard terminal. In the isolated-case or the emitter-and-case-common connection, the case is tied to the guard circuit. The guard circuit is also tied to the shielding. Note that the paralleled capacitances from the measure
27、ment terminals to the guard circuit are balanced out and do .not enter into the measurement. 2.2 cto-Case Capacitance Figure 6 shows the test circuit for the isolated-case condition ISOLATED CASE COMMON EMll7ER and CASE COMMON BASE and CASE COMMON COLLECTOR and CASE FIGURE 2 - EQUIVALENT CIRCUITS RS
28、-396 Page 6 TERMINAL-TO-TERMINAL TEST CONNECTIONS C ISOLATED CASE COMMON BASE end CASE COMMON EMITTER and CASE C COMMON COLLECTOR and CASE FIGURE 3 - MEASUREMENT OF Ccb NOTE: Various pieces of commercial equipment differ as to the designation of the measurement terminal which is nearest the ac poten
29、tial of the guard terminal. Here the base should be near the guard potential. RS-396 P-7 TERMINAL-TO-TERMINAL TEST CONNECTIONS E- ISOLATED CASE E COMMON EMITTER and CASE 6 B C E Case Z E E COMMON BASE and CASE COMMON COLLECTOR and CASE FIGURE 4 - MEASUREMENT OF Ceb NOTE: Various pieces of commercial
30、 equipment differ as to the designation of the measurement terminal which is nearest the ac potential of the guard terminal. Here the base should be near the guard potential. RS-396 Pago 9 TERMINAL-TO-TERMINAL TEST CONNECTIONS C ISOLATED CASE C COMMON BASE and CASE C COMMON EMITTER and CASE I28 J C
31、A.-r COMMON COLLECTOR end CIHX FIGURE 5 - MEASUREMENT OF C, NOTE: Various pieces of commercial equipment differ as to the designation of the measurement terminal which is nearest the ac potential of the guard terminal. Here the emitter should be near the guard potential. RS-396 pw9 ELECTRODE-TO-CASE
32、 TEST CONNECTIONS ISOLATED-CASE CONDITION Case MEASUREMENT OF C,(,) (collector (It guard potential) Case MEASUREMENT OF C, (emitter at guard potential) Case MEASUREMENT OF Cb,case, (base at guard potential) FIGURE 6 - MEASUREMENT OF ELECTRODE-TO-CASE CAPACITANCE NOTE: Various pieces of commercial eq
33、uipment differ es to the designation of the measurement terminal which i6 nearest the ac potential of the guard terminal. M-396 Pa#a 10 DEFINITIONS OF CAPAClTANCES USED External Capacitances to Ground (depends to a large extent on physical test configuration.) Cc(gnd) collector terminal stray capaci
34、tance to ground Ce(gnd) emitter terminal stray capacitance to ground Cb(gnd) base terminal stray capacitance to ground C(case)(gnd) case shield terminal stray capacitance to ground Element Capacitance to Case Shield (internal to the device) Cc(case) collector stray capacitance to case Ce(case) emitt
35、er stray capacitance to case Cb(case) base stray capacitance to case. Interelement Capacifance (internal to the device, reverse bias only) Ccb collector-base capacitance Ceb emitter-base capacitance Cce collector-emitter capacitance Interelement capacitance is primarily depletion layer capacitance p
36、lus stray connector-to-connector capacitance. It specifically excludes any capacitance to shield whether or not the shield is tied to any element and not directly separable. Measured Capacitances (use three-terminal guarded measurements - sometimes called “direct”) Ccb collector-to-base capacitance,
37、 emitter terminal connected to guard, collector reverse biased. Ceb emitter-to-base capacitance, collector terminal connected to guard, emitter reverse biased.2 Ccc collector-to-emitter capacitance, base terminal connected to guard, collector reverse biased.* Cc(case) collector-to-case capacitance,
38、emitter and base terminals connected to guard.s Ce(case) emitter-to-case capacitance, collector and base terminals connected to guard.s Cb(case) base-to-base capacitance, collector and emitter terminals connected to guard.” “Internal to the device” applies to the region of the device side of the reference plane. Includes only interelement capacitances plus capacitance to shield where the shield is tied to one of the terminals under measurement. 3Measurement possible only in the isolated-case configuration.
