THS6072 Datasheet, PDF (10/31 Pages) Texas Instruments – LOW-POWER ADSL DIFFERENTIAL RECEIVER

THS6072
LOW-POWER ADSL DIFFERENTIAL RECEIVER
SLOS290B – FEBRUARY 2000 – REVISED JUNE 2001
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
Assume: R_L = 100 Ω
V_noise = √(P×R) = √(0.01 fW × 100 Ω) = 31.6 nV/√Hz
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
1:1
1:2
Vnoise ON LINE
31.6 nV/√Hz
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-kΩ load
distortion is much better than a 150-Ω load.
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