EL2228

FN7008 Rev 2.00

Page 9 of 12

May 3, 2007

Applications Information

Product Description

The EL2228 is a dual voltage feedback operational amplifier

designed especially for DMT ADSL and other applications

requiring very low voltage and current noise. It also features

low distortion while drawing moderately low supply current

and is built on Elantec's proprietary high-speed

complementary bipolar process. The EL2228 uses a

classical voltage-feedback topology which allows them to be

used in a variety of applications where current-feedback

amplifiers are not appropriate because of restrictions placed

upon the feedback element used with the amplifier. The

conventional topology of the EL2228 allows, for example, a

capacitor to be placed in the feedback path, making it an

excellent choice for applications such as active filters,

sample-and-holds, or integrators.

Single-Supply Operation

The EL2228 was designed to have a wide input and output

voltage range. This design also makes the EL2228 an

excellent choice for single-supply operation. Using a single

positive supply, the lower input voltage range is within

range is within 875mV of ground. Upper input voltage range

reaches 3.6V, and output voltage range reaches 3.8V with a

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 EL2228 has a gain-bandwidth product of 40MHz while

using only 5mA of supply current per amplifier. For gains

greater than 1, their closed-loop -3dB bandwidth is

approximately equal to the gain-bandwidth product divided

by the noise gain of the circuit. For gains of 1, higher-order

poles in the amplifiers' transfer function contribute to even

higher closed loop bandwidths. For example, the EL2228

have a -3dB bandwidth of 80MHz at a gain of 1, dropping to

9MHz at a gain of 5. It is important to note that the EL2228 is

designed so that this “extra” bandwidth in low-gain

Pin Descriptions

8 Ld MSOP

8 Ld SOIC

PIN NAME

PIN

FUNCTION

EQUIVALENT CIRCUIT

11

Output

Circuit 1

22

Input

Circuit 2

33

Input

Reference Circuit 2

4

4

VS-

Supply

55

Input

66

Input

Reference Circuit 2

77

Output

Reference Circuit 1

88

Supply