Bipolar transistor current gain (beta, β) is the ratio of collector current to base current (β = I_C/I_B). A typical bipolar transistor used for op amps IC designs has a beta of 50 to 150 A/A. Super-beta transistors undergo additional processing to achieve beta exceeding 1,000 A/A. Since super-beta transistors have high current gain, the base current required to achieve a target collector current can be much lower than traditional bipolar transistors. The collector current of the differential input pair determines the bandwidth, slew-rate, noise, and other parameters. Thus, bipolar op amps that use super beta transistors have lower base current than comparable traditional bipolar op amps. The lower I_B not only lowers the error caused by the conversion of I_B to input offset voltage, but additionally improves the input bias current noise ( ${\mathrm{i}}_{\mathrm{n}}=\sqrt{2\mathrm{q}{\mathrm{I}}_{\mathrm{B}}}$ ). The super-beta technology can also be used with input bias current cancellation to further reduce I_B. Figure 2-13 compares the base current of a bipolar transistors with and without I_B cancellation to a super-beta transistor with I_B cancellation. The combination of both super-beta and bias current cancellation reduce I_B by a factor of 100 when compared to traditional amplifiers. Super-beta Input Amplifiers: Features and Benefits provides more details on this technology.

Figure 2-13 Super-beta vs Traditional Approaches