THS6072

LOW-POWER ADSL DIFFERENTIAL RECEIVER

SLOS290B – FEBRUARY 2000 – REVISED JUNE 2001

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

ADSL line noise

Per ANSI T1.413, the noise power spectral density for an ADSL line is –140 dBm/

√Hz. This results in a voltage

noise requirement of less than 31.6 nV/

√Hz for the receiver in an ADSL system with a 1:1 transformer ratio.

Noise Power Spectral Density = –140 dBm/

√Hz

Power = 1e–17

× 1 Hz = 0.01 fW

For ADSL systems that use a 1:2 transformer ratio, such as central office line cards, the voltage noise

requirement for the receiver is lowered to 15.8 nV/

√Hz.

TRANSFORMER

RATIO

Vnoise ON LINE

1:1

31.6 nV/

√Hz

1:2

15.8 nV/

√Hz

The THS6072 was designed to operate with 10 nV/

√Hz voltage noise, exceeding the noise requirements for

an ADSL system operating with 1:1 or 1:2 transformer ratios. For systems where a voltage noise of less than

10 nV/

√Hz voltage noise is required, see the THS6062 low noise ADSL receiver which operates with a voltage

noise level of 1.6 nV/

√Hz.

minimizing distortion

One way to minimize distortion is to increase the load impedance seen by the amplifier, thereby reducing the

currents in the output stage. This will help keep the output transistors in their linear amplification range and will

also reduce the heating effects. This can be seen in Figure 10 through Figure 13, which show a 1-k

Ω load

distortion is much better than a 150-

Ω load.