AMC2244/AMC2344/AMC2444

Copyright

© 2006 2006 ADDtek Corp.

8

DD006_E -- JUNE 2006

APPLICATION INFORMATION (CONTD.)

Single Supply Operation

The AMC2244/AMC2344/AMC2444 have been designed to operate over a wide input and output voltage range.

= 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

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

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

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.