The correct answer is: D. To amplify the input voltage.
Bipolar transistors are used to amplify the input voltage in BiCMOS. This is because bipolar transistors have a much higher current gain than MOSFETs. This means that a small change in the base current can cause a large change in the collector current. This makes bipolar transistors ideal for amplifying signals.
MOSFETs, on the other hand, have a much higher input impedance than bipolar transistors. This means that they are less susceptible to noise and interference. This makes MOSFETs ideal for driving high-impedance loads.
In BiCMOS, the bipolar transistors are used to amplify the input voltage, while the MOSFETs are used to drive the output loads. This combination of bipolar transistors and MOSFETs gives BiCMOS devices the best of both worlds: high gain and high input impedance.
Here is a brief explanation of each option:
- Option A: Drive input loads. This is not the main purpose of bipolar transistors in BiCMOS. Bipolar transistors are not as good at driving high-impedance loads as MOSFETs.
- Option B: Drive output loads. This is not the main purpose of bipolar transistors in BiCMOS. Bipolar transistors are not as good at driving high-impedance loads as MOSFETs.
- Option C: To perform logic functions. This is not the main purpose of bipolar transistors in BiCMOS. Bipolar transistors are not as good at performing logic functions as MOSFETs.
- Option D: To amplify the input voltage. This is the main purpose of bipolar transistors in BiCMOS. Bipolar transistors have a much higher current gain than MOSFETs, which makes them ideal for amplifying signals.