ADI电流反馈放大器设计说明

amp1.pdf : High speed analog signal processing applications, such as video and
communications, require op amps which have wide bandwidth, fast settling time,
low distortion and noise, high output current, good DC performance, and operate at
low supply voltages. These devices are widely used as gain blocks, cable drivers,
ADC pre-amps, current-to-voltage converters, etc. Achieving higher bandwidths for
less power is extremely critical in today's portable and battery-operated
communications equipment. The rapid progress made over the last few years in
high-speed linear circuits has hinged not only on the development of IC processes
but also on innovative circuit topologies.
The evolution of high speed processes by using amplifier bandwidth as a function of
supply current as a figure of merit is shown in Figure 1.1. (In the case of duals,
triples, and quads, the current per amplifier is used). Analog Devices BiFET process,
which produced the AD712 and OP249 (3MHz bandwidth, 3mA current), yields
about 1MHz per mA. The CB (Complementary Bipolar) process (AD817, AD847,
AD811, etc.) yields about 10MHz/mA of supply current. Ft's of the CB process PNP
transistors are about 700MHz, and the NPN's about 900MHz.
The latest generation complementary bipolar process from Analog Devices is a
high speed dielectrically isolated process called XFCB (eXtra Fast Complementary
Bipolar). This process (2-4 GHz Ft matching PNP and NPN transistors), coupled
with innovative circuit topologies allow op amps to achieve new levels of costeffective
performance at astonishing low quiescent currents. The approximate figure
of merit for this process is typically 100MHz/mA, although the AD8011 op amp is
capable of 300MHz bandwidth on 1mA of supply current due to its unique two-stage
current-feedback architecture.
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