OP AMP OUTPUT STAGES USING COMPLEMENTARY DEVICES ALLOW PUSH-PULL DRIVE NPN NPN NPN ONLY CLASS A NPN/PNP CLASS B Figure 1.6 An IC process with relatively well-matched (AC and dc)PNP and NPn transistors lows both the output voltage swing and slew rate to be reasonably well matched. However, an output stage using B Ts cannot swing completely to the rails, but only to within the transistor saturation voltage(V cesaR of the rails(see Figure 1.7) For small amounts of load current (less than 100u A), the saturation voltage may be as low as 5 to 10mv, but for higher load currents, the saturation voltage can increase to several hundred mv(for example, 500mv at 50mA) On the other hand, an output stage constructed of CMOS FETs can provide true rail-to-rail performance, but only under no-load conditions. If the output must source or sink current, the output swing is reduced by the voltage dropped across the FEts internal"on"resistance(typically, 100ohms)9 OP AMP OUTPUT STAGES USING COMPLEMENTARY DEVICES ALLOW PUSH-PULL DRIVE Figure 1.6 An IC process with relatively well-matched (AC and DC) PNP and NPN transistors allows both the output voltage swing and slew rate to be reasonably well matched. However, an output stage using BJTs cannot swing completely to the rails, but only to within the transistor saturation voltage (VCESAT) of the rails (see Figure 1.7). For small amounts of load current (less than 100µA), the saturation voltage may be as low as 5 to 10mV, but for higher load currents, the saturation voltage can increase to several hundred mV (for example, 500mV at 50mA). On the other hand, an output stage constructed of CMOS FETs can provide true rail-to-rail performance, but only under no-load conditions. If the output must source or sink current, the output swing is reduced by the voltage dropped across the FETs internal "on" resistance (typically, 100ohms)