Pnp transistor

The schematic of the temperature sensor on the bulk chip is shown in Fig. 5.3. The bulk chip temperature is measured via the voltage difference between a pair of diode-connected pnp-transistors (parasitic transistors as available in the CMOS process, collectors tied to substrate) working at different current densities. Transistor Qi is biased with a current of 40 pA, and transistor Q2 is biased with a current of 10 pA. 

The logarithmic converter is implemented with a voltage-to-current converter (OPAM, Ml, and Rs) and a pair of diode-connected, vertical pnp transistors (Qi and Q2). The relation between the differential output voltage (AVeb) and the sample resistance (Rs) is given by the equation ... 

The simulation results do not correlate well to the hardware. A possible cause is the ESR of a Mallory TDC106K505WSG 10 /U.F capacitor, C2. The feedback loop is originated at the collector of the PNP transistor to avoid sensitivity to the output capacitor s ESR. However, investigation into the poor correlation indicates that the circuit is sensitive to the ESR of capacitor C2. The ESR was measured using an HP 3577A network analyzer. The results are shown in Fig. 4.25. 

Junction transistors (Figs. 9.18A and 9.18B) can be synthesized in two ways (1) the grown-junction pnp transistor or (2) the fused-junction transistor... 

A bipolar transistor is a three terminal device which includes the components of emitter (E), base (B) and collector (C). There are two types of bipolar transistors, npn and pnp. The letters refer to the layers of semiconductor materials used to make the transistors. Fig. 9.3a, b shows the schematic illustrations of current flows and the circuit symbols of npn and pnp transistors. The shaded regions in the figure represent two depletion regions formed at the interfaces of emitter/base and base/collector. 

Electrical Characteristics of a BJT The discu.ssion that follows focuses on ilie behavior of a pnp-iypc RJT, It should be appreciated that the npn type acts analogously e. ccpi tor the direction of the curreni, which is opposite lo that of tlie pnp transistor. 

PNP transistor a transistor that is signaled by a negative charge. 

Figure 18.9 Schematic of an insulated-gate bipolar (pnp) transistor IGBT (a). The equivalent circuit (b) shows nicely that an IGBT consists of a MOSFET and a pnp transistor.

The basic operation of the PNP transistor is similar to that of the NPN, except for a reversal of the polarity of the algebraic signs of aU DC currents and voltages. 

Fig. 15.1 A PNP transistor in a "common base" arrangement. (All the currents go through the same base wire.)...

The wiring diagram for the common base experiment is Fig. 15.3. Note that the symbol for the PNP transistor only has one arrow, even though it really contains two diodes. The arrow is always on the "emitter." (Sometimes a circle is drawn around the whole transistor, although that type of symbol will not be used here.) Before the 9 volt battery is attached, the ohmmeter should show essentially infinite resistance, just as it did in the test. Thus there is no "output" current flowing. 

The NPN transistor is used in this hookup. If the device is in a TO-92 package, the leads will be as shown in Fig. 15.2, the same as with the PNP. Again, the first thing to do is test it with an ohmmeter, but the results should be the opposite of what was observed with the PNP transistor. That is, when the positive output of the meter is attached to the base of the NPN, and negative to either the collector or the emitter, there should be conductivity, but not when the leads are reversed. 

In the manufacture of a pnp transistor, the p region Is purposely much more heavily doped than is the n region.. As a consequence, the concentration of holes in the p region is 100 times the concentration of mobile electrons in the n layer. Thus, the fraction of the current carried by holes is perhaps 100 times the fraction carried by electrons. 

After the discovery Shockley developed a basic transistor theory. Practically he replaced (in 1951) the point contact with a junction system. The bipolar junction transistor may consist of three layers, farthest out emitter and collector of p-type (compare chapter 40 SiHcon) and between them a base layer of n-type (pnp transistor). The... 

Schematic of a pnp transistor. An npn transistor is similar except the n and p are interchanged.

Common base amplifier circuit using a pnp transistor. An equivalent circuit can be constructed using an npn transistor by reversing the above polarities. 

If a curve tracer is not available in your laboratory, you can construct the very simple transistor tester of Fig. 6.8. The tester accepts on two different sockets both NPN and PNP transistor. The two-position, two-pole switch selects either type. The tester is basically a B meter and is surely much more effective than a simple ohmmeter employed to determine whether either junction is open or not. With the tester of Fig. 6.8 you put the transistor under test on the relevant socket having previously correctly positioned the switch, and take note of the panel meter reading. If such a reading is between 0 and 3V, your transistor has to be replaced. 

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