The EL2227 is a dual low noise amplifier ideal for line reception applications in ADSL and HDSLII designs. The low noise specification of the EL2227 is only 1.9nv/hz and 1.2pa/hz, making it ideal for detecting very low amplitude signals. The EL2227 features a -3dB bandwidth of 115MHz with a gain of 2 stability. The EL2227 also offers minimal power dissipation, drawing only 4.8mA of supply current per amplifier. The amplifier can be powered from ±2.5 V to ±12 V. The EL2227 is available in a space-saving 8LD MSOP package, as well as an industry standard 8LD SOIC. It can operate in a temperature range of -40°C to +85°C.

Product Description

The EL2227 is a dual voltage feedback operational amplifier designed especially for applications such as DMT ADSL that require 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 EL2227 uses the classic voltage feedback topology to be used in various applications, making them current feedback amplifiers due to the inappropriate placement of the feedback components used with the amplifiers. The traditional EL2227 topology allows, for example, a capacitor to be placed in the feedback path, making it the best choice for applications such as active filters, sample-and-hold, or integrators.

figure 1

ADSL CPE application

The Low Noise Amplifier EL2227 is specially designed for Transceiver Hybrid and other Low Noise Amplifier applications with ADSL Dual Differential Receiver Amplifier function. A typical ADSL CPE line interface circuit is shown in Figure 1. The EL2227 is used for the received DMT downstream signal. With careful transceiver design hybrid and EL2227 1.9nV/√Hz voltage noise and 1.2pA/√Hz current noise performance, -140dBm/Hz regime background noise performance can be easily achieved.

Disable function

The EL2227 is a standard dual channel amplifier package with no enable/disable function. A simple way to implement the enable/disable functionality is described below. When disabled, both positive and negative supply voltages are disconnected (see Figure 2).

figure 2

Power dissipation along with the wide supply voltage range and large output drive capability of the EL2227 may exceed the maximum junction temperature of 150°C under certain load and supply conditions. Therefore, it is important to calculate the maximum junction temperature (TJMAX) for all applications to determine whether the supply voltage, load conditions, or package type need to be modified for the EL2227 to remain within the safe operating area. The relationship of these parameters is as follows:

printed circuit board layout

The EL2227 is very well behaved and easy to apply in most applications. However, a few simple tips will help guarantee fast, high-quality results. As with any high frequency device, good PCB layout is necessary to optimize performance. Ground plane construction is highly recommended as it is a good power bypass. A 0.1µF ceramic capacitor is recommended for bypassing the two consumables. 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 capacitance should be kept to a minimum, at both the input and at the output. The resistor value should be kept at 5kΩ because of the capacitance under the RC time constant related to parasitics. Both metal-film and carbon resistances are acceptable, the use of wirewound resistors is not recommended due to their parasitic inductance. Again, capacitors should be low inductance for best performance.