_

+

6.8

µF

0.1

µF

–15 V

6.8

µF

0.1

µF

15 V

1 k

Ω

1 k

Ω

+

+

VI+

_

+

6.8

µF

0.1

µF

–15 V

6.8

µF

0.1

µF

15 V

1 k

Ω

1 k

Ω

+

+

VI–

+

–

1 k

Ω

0.1

µF

1 k

Ω

2 k

Ω

12.5

Ω

+

–

1 k

Ω

0.1

µF

1 k

Ω

2 k

Ω

1:2

Telephone Line

12.5

Ω

–15 V

15 V

15 V

–15 V

0.01

µF

THS6062

THS6062

VO+

VO–

THS6012

Driver 1

THS6012

Driver 2

100

Ω

THS6012

SLOS226F – SEPTEMBER 1998 – REVISED JUNE 2012

www.ti.com

Figure 47. THS6012 ADSL Application

The ADSL transmit band consists of 255 separate carrier frequencies each with its own modulation and

amplitude level. With such an implementation, it is imperative that signals put onto the telephone line have as low

a distortion as possible. This is because any distortion either interferes directly with other ADSL carrier

frequencies or it creates intermodulation products that interfere with ADSL carrier frequencies.

The THS6012 has been specifically designed for ultra low distortion by careful circuit implementation and by

taking advantage of the superb characteristics of the complementary bipolar process. Driver single-ended

distortion measurements are shown in Figure 28 through Figure 31. It is commonly known that in the differential

driver configuration, the second order harmonics tend to cancel out. Thus, the dominant total harmonic distortion

(THD) will be primarily due to the third order harmonics. For these tests the load was 25

Ω. Additionally,

distortion should be reduced as the feedback resistance drops. This is because the bandwidth of the amplifier

increases, which allows the amplifier to react faster to any nonlinearities in the closed-loop system.

Another significant point is the fact that distortion decreases as the impedance load increases. This is because

the output resistance of the amplifier becomes less significant as compared to the output load resistance.

26

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