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FN7058.4
September 14 ,2010
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Single-Supply Operation
The EL2227s have been designed to have a wide input and
output voltage range. This design also makes the EL2227 an
excellent choice for single-supply operation. Using a single
positive supply, the lower input voltage range is within
200mV of ground (R
L
= 500), and the lower output voltage
range is within 875mV of ground. Upper input voltage range
reaches 3.6V, and output voltage range reaches 3.8V with a
5V supply and R
L
= 500. This results in a 2.625V output
swing on a single 5V supply. This wide output voltage range
also allows single-supply operation with a supply voltage as
high as 28V.
Gain-Bandwidth Product and the -3dB Bandwidth
The EL2227s have a gain-bandwidth product of 137MHz
while using only 5mA of supply current per amplifier. For
gains greater than 2, their closed-loop -3dB bandwidth is
approximately equal to the gain-bandwidth product divided
by the noise gain of the circuit. For gains less than 2, higher
order poles in the amplifiers' transfer function contribute to
even higher closed loop bandwidths. For example, the
EL2227 have a -3dB bandwidth of 115MHz at a gain of +2,
dropping to 28MHz at a gain of +5. It is important to note that
the EL2227 have been designed so that this “extra”
bandwidth in low-gain applications does not come at the
expense of stability. As seen in the typical performance
curves, the EL2227 in a gain of +2 only exhibit 0.5dB of
peaking with a 1000 load.
Output Drive Capability
The EL2227s have been designed to drive low impedance
loads. They can easily drive 6V
P-P
into a 500 load. This
high output drive capability makes the EL2227 an ideal
choice for RF, IF and video applications.
Printed-Circuit Layout
The EL2227s are well behaved, and easy to apply in most
applications. However, a few simple techniques will help
assure rapid, high quality results. As with any high-frequency
device, good PCB layout is necessary for optimum
performance. Ground-plane construction is highly
recommended, as is good power supply bypassing. A 0.1µF
ceramic capacitor is recommended for bypassing both
supplies. Lead lengths should be as short as possible, and
bypass capacitors should be 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 kept under 5k because
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 for best performance.
TABLE 1.
PART PACKAGE
JA
MAX PDISS @
T
MAX
MAX V
S
EL2227CS SO8 160°C/W 0.406W @ +85°C
EL2227CY MSOP8 206°C/W 0.315W @ +85°C
EL2227
