Measurement of high-frequency equivalent circuit parameters of junction and surface barrier transistors

Methods are described for the determination of the high-frequency parameters of junction and surface barrier transistors and involve, in addition to the knowledge of the usual low-frequency parameters, measurement of the product of C
c
and the extrinsic base resistance
r_{b0}
,
r_{b0}
itself, and the alpha cutoff frequency f
α
. A previously described method is used to determine the product
r_{b0}C_{c}
, but new methods are described for the measurement of
r_{b0}
and f
α
. The measurements are of "bridge" type, involving simple circuit adjustments for a response null at a single frequency. Typical experimental results are given for transistors having f
α
values as high as 85 mc, C
c
values down to 2.3 pF and
r_{b0}
ranging from 45 to 400 ohms. The limits quoted for f
α
and C
c
refer to surface barrier transistors. Comparison with results derived by alternative methods of measurement show good agreement.