CMX868 查看數據表（PDF） - MX-COM Inc

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CMX868

Low power V.22 bis modem

MX-COM Inc  

Low Power V.22bis Modem

12

CMX868 Advance Information

4.3 Tx Filter and Equalizer

The FSK or QAM/DPSK modulator output signal is fed through the Transmit Filter and Equalizer block which

limits the out-of-band signal energy to acceptable limits. In 600, 1200 and 2400bps FSK, DPSK and QAM

modes this block includes a fixed compromise line equalizer which is automatically set for the particular

modulation type and frequency band being employed. This fixed compromise line equalizer may be enabled

or disabled by bit 10 of the General Control Register. The amount of Tx equalization provided compensates

for one quarter of the relative amplitude and delay distortion of ETS Test Line 1 over the frequency band

used.

4.4 DTMF/Tone Generator

In DTMF/Tones mode this block generates DTMF signals or single or dual frequency tones. In QAM/DPSK

modem modes, it is used to generate the optional 550 or 1800Hz guard tone.

4.5 Tx Level Control and Output Buffer

The outputs (if present) of the Transmit Filter and DTMF/Tone Generator are summed then passed through

the programmable Tx Level Control and Tx Output Buffer to the pins TXA and TXA . The Tx Output Buffer

has symmetrical outputs to provide sufficient line voltage swing at low values of VDD and to reduce harmonic

distortion of the signal.

4.6 Rx DTMF/Tones Detectors

In Rx Tones Detect mode the received signal, after passing through the Rx Gain Control block, is fed to the

DTMF / Tones / Call Progress / Answer Tone detector. The user may select any of four separate detectors:

The DTMF detector detects standard DTMF signals. A valid DTMF signal will set bit 5 of the Status Register

to 1 for as long as the signal is detected.

The programmable tone pair detector includes two separate tone detectors (see Figure 20). The first detector

will set bit 6 of the Status Register for as long as a valid signal is detected, the second detector sets bit 7, and

bit 10 of the Status Register will be set when both tones are detected.

The Call Progress detector measures the amplitude of the signal at the output of a 275 - 665Hz bandpass

filter and sets bit 10 of the Status Register to 1 when the signal level exceeds the measurement threshold.

10

0

-10

-20

dB

-30

-40

-50

-60

0

0.5

1

1.5

2

2.5

3

3.5

4

kHz

Figure 9: Response of Call Progress Filter

The Answer Tone detector measures both amplitude and frequency of the received signal and sets bit 6 or bit

7 of the Status Register when a valid 2225Hz or 2100Hz signal is received.

¤2001 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. # 20480205.007

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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