Moteur de recherche de fiches techniques de composants électroniques |
|
SL6649-MPES Fiches technique(PDF) 5 Page - Zarlink Semiconductor Inc |
|
SL6649-MPES Fiches technique(HTML) 5 Page - Zarlink Semiconductor Inc |
5 / 14 page SL6649-1 4 PRINCIPLE OF OPERATION The incoming signal is split into two parts and frequency converted to baseband. The two paths are produced in phase quadrature (see Fig 2) and detected in a phase detector which provides a digital output. The quadrature network must be in the local oscillator path. At a data rate of 512 baud and a deviation frequency of 4.5kHz, the input to the system has a demodulation index of 18. This gives a spectrum as in Fig 3. f 1 and f 0 represent the ‘steady state’ frequencies (i.e. modulated with continuous ‘1’ and ‘0’ respectively). The spectrum in Fig 3 is for reversals (a 0-1-0-1-0-1 etc. pattern) at the system bit rate; f C is the nominal carrier frequency). When the LO is at the nominal carrier frequency, then a continuous ‘0’ or ‘1’ will produce an audio frequency, at the output of the mixers corresponding to the difference between f 0 and f C or f 1 and f C . If the LO is precisely at fc, then the resultant output signal will be at the same frequency regardless of the data state; nevertheless, the relative phases of the two paths will reverse between ‘0’ and ‘1’ states. By applying the amplified outputs of the mixers to a phase discriminator, the digital data is reproduced. TUNING THE CHANNEL FILTERS The adjacent channel rejection performance of the SL6649-1 receiver is determined by the channel filters. To obtain optimum adjacent channel rejection, the channel filters’ cut off frequency should be set to 8kHz. The process tolerances are such that the cut off frequency cannot be accurately defined, hence the channel filters must be tuned. However the receiver characteristics on the previous page can be achieved with a fixed 270k Ω resistor between pin 3 and GND. Tuning is performed by adjusting the current in the gyrator circuits. This changes the values of the gyrator’s equivalent inductance. The cut off frequency is tuned to 8kHz. To accurately define the cut off of the channel filters, a gyrator based Colpitts oscillator circuit has been included on the SL6649-1. The Colpitts oscillator and channel filters use the same type of architecture, hence there is a direct correlation between oscillator frequency and cut off frequency. By knowing the Colpitts oscillator frequency the channel filter cut off frequency can be estimated from Figure 4. Once the channel filters have been tuned it may be necessary to disable the Colpitts oscillator. The Colpitts oscillator is disabled by connecting the Colpitts oscillator output/disable pin (pin # 16) to V CC 2. This is needed since the Colpitts oscillator may impair the performance of the receiver. Figure 3: Spectrum Diagram Figure 4 Figure 5: Channel Filter Response k k k |
Numéro de pièce similaire - SL6649-MPES |
|
Description similaire - SL6649-MPES |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |