AMC2244/AMC2344/AMC2444
APPLICATION INFORMATION (CONTD.)
Single Supply Operation
The AMC2244/AMC2344/AMC2444 have been designed to operate over a wide input and output voltage range.
However, the AMC2244/AMC2344/AMC2444 are also suitable for single-supply operation. With a 5V supply and R
L
= 500Ω, the output voltage swing is from 200mV to 3.9V, this results in a 3.7V output swing on a single 5V supply.
The single supply operation range is from as high as 36V to 2.5V. For a single 2.5V supply application, the output
swing can still have 1V
PP
.
Gain-Bandwidth Product and the-3 dB Bandwidth
The gain-bandwidth product of AMC2244/AMC2344/AMC2444 is 60 MHz while using only 7mA of supply current
per amplifier. For gains greater than 4, their closed-loop –3 dB bandwidth is approximately equal to the
gain-bandwidth product divided by the noise gain of the circuit. For gains less than 4, higher-order poles in the
amplifiers’ transfer function contribute to even higher closed loop bandwidths. For example, the –3 dB bandwidth is
120 MHz at a gain of + 1, dropping to 60 MHz at a gain of +2.
Output Drive Capability
The AMC2244/AMC2344/AMC2444 have been designed to drive low impedance loads. The output swing can easily
reach 6V
PP
into a 150Ω load. This features the AMC2244/AMC2344/AMC2444 in the field of RF, IF and video
applications. Furthermore, even at low temperatures, the current drive still remains a minimum of 35mA.
For signal transmission and distribution, a back-terminated cable (75Ω in series at the drive end, and 75Ω to ground at
the receiving end) is preferred since the impedance match at both ends will absorb any reflections. However, when
double termination is used, the received signal is halved; therefore a gain of 2 configuration is typically used to
compensate for the attenuation.
Capacitive Loads
While driving the capacitive loads, the AMC2244/AMC2344/AMC2444 remain stable by automatically reducing their
gain-bandwidth product as capacitive load increases. Therefore, for maximum bandwidth, capacitive loads should be
reduced as much as possible or isolated via a series output resistor (R
S
). Similarly, coax lines can be driven, but best
AC performance is obtained when they are terminated with their characteristic impedance so that the capacitance of
the coaxial cable will not add to the capacitive load seen by the amplifier. Although stable with all capacitive loads,
some peaking still occurs as load capacitance increases. A series resistor at the output can be used to reduce this
peaking and further improve stability.
Printed-Circuit Layout
In most applications, good PCB layout is necessary for optimum performance. Ground-plane construction is highly
recommended for good power supply bypassing. A 0.1 µF ceramic capacitor is recommended for bypassing both
supplies. Lead lengths should be as short as possible, and bypass capacitors should be placed as close to the device
pins as possible. For good AC performance, parasitic capacitances should be kept to a minimum at both inputs and at
the output. Resistor values should be dept under 5 KΩbecause of the RC time constants associated with the parasitic
capacitance. Metal-film and carbon resistors are both acceptable, use of wire-wound resistors is not recommended
because of their parasitic inductance. Similarly, capacitors should be low-inductance foe best performance.
Copyright
©
2006 2006 ADDtek Corp.
8
DD006_E
-- JUNE 2006
ADDTEK [ ADDTEK CORP ]
