Moteur de recherche de fiches techniques de composants électroniques |
|
SL1466 Fiches technique(PDF) 11 Page - Zarlink Semiconductor Inc |
|
SL1466 Fiches technique(HTML) 11 Page - Zarlink Semiconductor Inc |
11 / 18 page 10 SL1466 Adjust the tank coil by squeezing it slightly until the signal on both Pins goes high (i.e. > Vcc –0.4 Volts). These Pins remain high provided the LO frequency is tuned to within the AFC WINDOW aperture,( ± 0.22MHz). Optimising the loop components The network connected from Pin 26 (VIDEO+) to Pin 24 (VIDEOFB–) and from Pin 25 (VIDEO–) to Pin 27 (VIDEO FB+) forms the loop filter. The components shown are based on a natural frequency ƒn of 2.46MHz ( ω n =2x π x2.46 Mrads/s ) and damping factor ξ =2.6, and assuming Ko = 54MHz/V. The closed loop gain of the receiver (i.e. the ratio of the output amplitude to the input carrier frequency variation versus frequency) has a low pass filter characteristic. Its roll off is determined by the natural frequency whilst its in band flatness is determined by the damping factor. Both factors will affect the 3dB bandwidth as discussed earlier. A narrow bandwidth will cause loss of high frequency resolution whilst a large bandwidth will degrade the overall signal/noise in the output waveform. Thus a selection procedure might be as follows: I Calculate R7 (R9) and C9 (C14) based on ƒ n = 2.46MHz, ξ =2.6 and connect as in Fig. 5. I Set the video generator for 1Vp–p composite video and the test generator for a carrier frequency of 479.5MHz, frequency deviation of 13.5MHz and power level –30dBm. I Turn on the pre–emphasis filter. Use the 15kHz test pattern to give black/white screen. I Monitor the video analyser or TV set. I Adjust the de–emphasis filter until the bar amplitude is 1Vp–p or 0% error. Reduce transmitter power level until sparklies or streaking appear. I Adjust component values for minimum power level when streaking and sparklies occur together. AGC settings The signal level at the input to the limiter preceding the phase detector is maintained at an level of around –20dBm or more by an internal (device) AGC and an external (tuner) AGC circuit. Current pulses at the carrier frequency with mark/space proportional to this input power are sourced out of pin 18 (AGC TIME CONSTANT). These are smoothed and turned into a voltage by the external components R4, C4. The time constant R4 C4 should be adjusted so that the expected signal fading rate can be tracked but its value is not critical, 5mSec typically. Fig. 4 shows a typical external AGC control curve. Also shown is the AGCTIMECONST voltage which is an indication of the level of internal AGC gain being applied, (the control range is the flat part of the curve). APPLICATION NOTES Tuning procedure The component values shown in the applications circuit Fig. 6 are optimised for operation at an IF of 479.5MHz. The AFC circuit can be used to fine tune the external tank as follows: With the SL1466 connected as in the test set up Fig. 11 or its equivalent using 75 Ω cables. Set the video generator for 1V p-p output. Set the satellite test transmitter for a carrier frequency of 479.5MHz, frequency deviation 13.5MHz, power level -30dBm. Turn on the pre-emphasis filter. Monitor the voltage levels on Pin 2 (DIGFLO) and Pin 3 (DIGFHI). |
Numéro de pièce similaire - SL1466 |
|
Description similaire - SL1466 |
|
|
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 |