HT9015 datasheet(18/23 Pages) HOLTEK

18 / 23 page

HT9015

April 10, 2000

Preliminary

No i s e

- 15. 2 5dB V

- 25. 2 5dB V

- 35. 2 5dB V

- 45. 2 5dB V

- 10. 5 d B V

- 20dB V

- 30dB V

- 40dB V

- 50dB V

- 60dB V

- 70dB V

- 80dB V

0dB V

- 5dB V

- 10. 5 d B V

- 20dB V

- 30dB V

- 40dB V

- 50dB V

- 60dB V

- 70dB V

- 80dB V

0dB V

- 5dB V

- 7. 75 dB V

C o m p r e sso r

I npu t

C o m p r e sso r

O u t put

T r ans m i s s i on

M edi um

E x pander

I npu t

E x pander

O u t put

Figure 9 Illustration of compressed and extended signal

Compander

The compander (compressor and expander) is

composed of two variable gain circuits which

provide compression and expansion of the sig-

nal dynamic range. In consideration of the wide

band noise and maximum dynamic range

which exist in the transmission medium, the

general signal handling technique lowers the

general communication quality by reducing the

S/N ratio and generating a clipping phenome-

non. However the compander improves the

communication quality by automatically con-

trolling the gain based on the input signal level

to increase the valid dynamic range and to im-

prove the S/N ratio.

In the HT9015, the compressor will take a sig-

nal with a 75dB dynamic range (-5dB to

-80dB), and reduce it to a 37.5dB dynamic

range (-7.5dB to -45dB) by attenuating strong

signals,while amplifying low level signals. The

expander does the opposite in that the 37.5dB

signal range is increased to a dynamic range of

75dB by amplifying strong signals and attenu-

ating low level signals. The 0dB level is inter-

nally set at 316.227mVrms - that is the signal

level which is neither amplified nor attenuated.

See Figure 9 below. Through the action of the

compander, the noise of the transmission me-

dium is constant under -80dBV.

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