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Ultra low noise amplifiers.  (part 5)

Noise measurements of several PNP transistors.
(For NPN transistors, see part3 )

On this page, the noise performance of several PNP transistors is tested.

Figure 1, this is the amplifier I use for measuring the noise of a PNP transistor.
The circuit is very similar to the circuit used for measuring NPN transistors which you find in
part3 , where you can find some information on the working of the circuit.

This PNP version works on -12 volt, while the NPN version works on +12 volt.
Therefore the polarity of the electrolytic capacitors and diode D1 is reversed.

Figure 2, the amplifier for measuring the PNP transistor noise.
The transistor under test is hanging on the three green wires.

 Transistor type Manufacturer View datasheet of transistor hfe  at 25°C Ic=10 mA Measured input noise of test amplifier at 1 kHz, Ic =10 mA. nV/√Hz Calculated  transistor base resistance Rbb  (Ω) Calculated Input noise of only the transistor. (R_circuit = 0Ω) at 1 kHz, Ic=10 mA. nV/√Hz View spectrum of measurement. Ic=10 mA. 2SAR293PFRA Rohm 2SAR293PFRA 490 0.995 56.97 0.982 Spectrum_2SAR293PFRA.jpg 2SAR542PFRA Rohm 2SAR542PFRA 320 0.445 9.14 0.416 Spectrum_2SAR542PFRA.jpg 2STR2230 ST 2STR2230 600 0.482 11.22 0.455 Spectrum_2STR2230.jpg BC327-40 Philips BC327 450 1.054 64.27 1.042 Spectrum_BC327-40.jpg FZT788B Diodes inc. / Zetex FZT788B 725 0.528 14.02 0.504 Spectrum_FZT788B.jpg FZT1149A Diodes inc. / Zetex FZT1149A 410 0.420 7.84 0.389 Spectrum_FZT1149A.jpg FZT1151A Diodes inc. / Zetex FZT1151A 450 0.420 7.84 0.389 Spectrum_FZT1151A.jpg PBSS5540Z NXP PBSS5540Z 330 0.341 4.21 0.302 Spectrum_PBSS5540Z.jpg STN790A ST STN790A 195 0.341 4.21 0.302 Spectrum_STN790A.jpg STN951 ST STN951 300 0.308 2.91 0.264 Spectrum_STN951.jpg ZTX751 Diodes inc. / Zetex ZTX751 225 0.330 3.76 0.289 Spectrum_ZTX751.jpg ZTX790A Diodes inc. / Zetex ZTX790A 490 0.396 6.65 0.363 Spectrum_ZTX790A.jpg ZTX951 Diodes inc. / Zetex ZTX951 200 0.277 1.82 0.227 Spectrum_ZTX951.jpg ZTX1149A Diodes inc. / Zetex ZTX1149A 410 0.415 7.59 0.383 Spectrum_ZTX1149A.jpg ZXT13P12DE6 Diodes inc. / Zetex ZXT13P12DE6 500 0.628 21.00 0.608 Spectrum_ZXT13P12DE6.jpg ZXTP2012Z Diodes inc. / Zetex ZXTP2012Z 250 0.341 4.21 0.302 Spectrum_ZXTP2012Z.jpg ZXTP25020DFL Diodes inc. / Zetex ZXTP25020DFL 450 0.535 14.47 0.511 Spectrum_ZXTP25020DFL.jpg

This table gives an overview of the transistors tested, with the measured input voltage noise of the test amplifier, and the calculated base resistance Rbb of the transistors.
Also the voltage noise of only the transistor is calculated at 10 mA collector current.
For an explanation of the Rbb value, see part 4 .
The collector current of the transistors is in all cases 10 mA.
For all transistors, the Rbb value was determined from the noise at 1 kHz.

In the next figure, the input noise voltages of all measured transistors are plotted in one diagram.

Figure 3, input noise voltage of the test setup, with different input transistors.

For this diagram, I compensated the values for the frequency response of the test setup.
Figure 4 shows the test setup response, and the compensation I applied for making figure 3.

Figure 4, frequency response of test setup, and the compensation curve.

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