CMX264 Просмотр технического описания (PDF) - MX-COM Inc

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CMX264

Frequency Domain Split-Band Scrambler

MX-COM Inc  

Frequency Domain Split-Band Scrambler

15

CMX264 Advance Information

Operating Characteristics Notes:

1. Not including any current drawn from the device pins by external circuitry.

2. This ignores the effects of pre-emphasis and de-emphasis, if selected.

3. Relative to a single tone at the MICIN pin. Because of the frequency inversion of the scrambling process,

the output frequency will not in general be equal to the input frequency. However, the scramble signal

output MICO will typically be within the limits given by Figure 3, Figure 4, Figure 5, or Figure 6. The

scrambled signal upper roll-off is defined by the filter TXUBOPF (Figure 7).

4. Filtering within the host equipment should ensure compliance with statutory transmission requirements

e.g. removal of a 4kHz SAT tone. See Figure 8 for a typical transmit filter which would be used to

accomplish this.

5. Not applicable within the region of the split point.

In transmit, the upperband is shifted upwards away from the lowerband so that there is a gap in the

scrambled spectrum. This avoids aliasing between the two bands in the recovered audio. See Figure 3,

Figure 4, Figure 5, and Figure 6 which show these gaps for each split point.

6. An output may be de-activated by powersaving the whole device (D10 = 0) or by deselecting it by means

of the relevant control bit (D6, D7 or D8) or, for the RECO and EXTO outputs, by setting the MUTERX pin

to logic ‘1’

7. With a single tone at the relevant input pin (MICIN or RXIN).

8. This parameter specifies the level of any unwanted spurious tones relative to the expected output tone,

whether that wanted tone is frequency shifted or not. The unwanted tones may be the result of carrier

breakthrough, baseband breakthrough or other aliasing effects.

9. Measured at the output of the host transmit radio filter, such as shown in Figure 8.

10. The distortion figure of the expected output tone, whether that wanted tone is frequency shifted or not.

This parameter is defined as the rms value of the spurious tones specified in Note 8 plus the noise within

the measurement bandwidth, divided by the rms value of the total signal, i.e. the wanted signal plus noise

plus spurious tones.

11. Specified over the complete scrambling/descrambling process i.e. scrambling by the Tx channel of the

transmitting device, typical radio channel filtering such as shown in Figure 8 and descrambling by the Rx

channel of the receiving device. The typical Rx channel passband gain of the CMX264 receive section

only is -1.0dB.

12. Not applicable in the region of the split point.

The response may exceed these limits within ±0.3 octaves of the frequencies 1950Hz, 1420Hz, 1180Hz

and 980Hz (for split points 1 to 4, respectively). Also, it may be outside ±3dB within ±0.15 octaves of the

frequencies 1900Hz, 1450Hz, 1210Hz and 1000Hz (for split points 1 to 4, respectively). In the recovered

audio, some of the energy at the split point will have been transmitted in the lowerband and some will

have been transmitted in the upperband. When the Rx device reconstitutes the signal, frequencies in the

vicinity of the split point will consist of signals summed together which have a random phase in relation to

each other. The relative phase will change over time so that the signals will vary between reinforcing

each other or canceling each other, thus taking the response outside the given limits.

13. See Figure 9 for typical responses of the pre/de-emphasis circuits.

14. The internal state of the device is controlled by the data D0-D10 input at the serial interface. Data should

not be loaded until 3ms after initial power up to allow the reset circuit to complete its operation and exit

the RESET state.

15. No filtering is performed in clear mode, however there is a possibility of aliasing at 63.337kHz

(see Section 5.2.1).

2000 MX-COM, Inc.

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

Doc. # 20480210.002

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All Trademarks and service marks are held by their respective companies.

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