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Transistor Specification Selection Guide Bias Current Range   Microcurrent Bipolar Transistors   AT-305xx   1 mA   noise bias     5 mA   power bias     AT-310xx   1 mA     10 mA     AT-320xx   2 mA     20 mA     Isolated Collector Transistors   HBFP-0405   2 mA   noise bias     5 mA   power bias     HBFP-0420   2 mA     20 mA     HBFP-0450   10 mA     //50 mA   Conventional Bipolar Transistors   AT-415xx   5 mA   noise bias     25 mA   power bias     AT-414xx   10 mA     25 mA     AT-420xx   10 mA     35 mA   AT-640xx   //110 mA     1        5         10         15         20         25         30         35         //     Collector Current [mA]     PHEMTs   ATF-35xxx   5 mA   noise bias     30 mA   power bias     ATF-36xxx   10 mA     10 mA     ATF-38xxx   10 mA     20 mA     ATF-34xxx   20 mA     60 mA     ATF-33xxx   30 mA     80 mA     MESFETs   ATF-26xxx   10 mA   noise bias     30 mA   power bias     ATF-13xxx   15 mA     40 mA     ATF-21xxx   15 mA     70 mA     ATF-10xxx   25 mA     70 mA       0     10       20       30       40       50       60       70       80       90       100     Drain Current [mA]       Power FETs   ATF-46xxx   125 mA   ATF-45xxx   250 mA   ATF-44xxx   500 mA     0     50       100       150       200       250       300       350       400       450       500     Drain Current [mA]   What: The Class A bias current level at which a transistor is operated (Class A operation is where the bias current does not change with RF drive). Bipolars specify the collector current, Ic. FETs specify the drain current, Id. Bias current must be adjusted appropriately for expected device performance. Most transistor data sheets contain information at both a noise bias (low current, best noise figure performance) and a power bias (high current, best P1dB). Noise figure has an optimum current, both above and below which performance rolls off. Power generally increases with the square of the current (the exception is when the device is voltage-swing limited). Gain also generally increases with current (implying a device can be used to higher frequencies when biased harder). Power devices change bias with drive. Many are specified with a quiescent current (Icq for bipolars, Idq for FETs), the bias current before RF is applied. (This kind of operation is called AB bias). Direction: needs to fit application Range: <1 to 500 mA

this page last updated: 20 October 1999