Op Amp Booster Designs

　　Although modern integrated circuit operational amplifiers ease linear circuit design， IC processing limits amplifier output power. Many applications， however， require substantially greater output voltage swing or current （or both） than IC amplifiers can deliver. In these situations an output “booster，” or post amplifier， is required to achieve the needed voltage or current gain. Normally， this stage is placed within the feedback loop of the operational amplifier so that the low drift and stable gain characteristics of the amplifier are retained. Because the booster is a gain stage with its own inherent AC characteristics， the issues of phase shift， oscillation， and frequency response cannot be ignored if the booster and amplifier are to work well together. The design of booster stages which achieve power gain while maintaining good dynamic performance is a difficult challenge. The circuitry for boosters will change with the application’s requirements， which can be very diverse. A typical current gain stage is shown in Figure 1.