1 introduction
The digital satellite multi-star many machine receive plan’s development stems from the people to use the satellite resources fully the idea. Usually uses 2 ways: First, may rotate the antenna with the single high frequency tuner coordination, uses DISEQC1.2 to control the rotation satellite receiving antenna to realize to the multi-star downward signal receive; Second, with many fixed high frequency tuners, uses DIsEQC1.0 or DISEQC2.0 coordinates the DISEQC switch selective channel to realize the multi-star receive. The former commonly used in single plane multi-star receive situation; The latter may use in many machine receives, but each receive confidential with an independent downward electric cable, connects the DISEQC switch’s to set-top box between circuit.
Has the massive idle frequency band existence according to the satellite digital television standard satellite downward channel pass band scope. Receives from the satellite to the electromagnetic wave gathers the voltage signal which transforms to high frequency tuner’s feed source, carries on frequency conversion processing for the high frequency tuner, in this case, after the high frequency tuner falls the frequency the intermediate frequency signal in does not have in the multiplying situation, the intermediate frequency signal band width also has the massive idle frequency band existence. This enables the signal the multiplying possibly to become.
2 hardware circuit’s design
The author designs a signal processing module, outputs the multi-channel signal multiplyings the high frequency tuner to a circuit, uses a down link cable to transmit the satellite receiver. This plan will design the good signal processing module to seal, on the one hand the user does not need independently to design the multi-channel choice lines, on the other hand may avoid under the DISEQC plan the many downward electric cable’s wiring numerous and diverse questions.
The signal processing module’s core function is single cable connection (SCIF), the frequency changer (LNB) output’s multi-channel signals carries on processing to the low noise under. This design the signal processing module and the LNB integration, as shown in Figure 1. Receives from the feed source without processing satellite signal bank 1~bank m, passes through the processing multiplying to a channel on, replaces in the DISEQC plan through the simple root down link cable many line cable to realize the downward transmission, assigns again through the power divider for many receiver uses.
2.1 multiplying principles
Intermediate frequency signaling frequency scope which outputs after the high frequency tuner between 950~2150MHz, each channel accounts for according to the above frequency band scope certain band width. When looker-in television program, only need guarantee in the program related band width the signal to the signal processing process in not affected. This hardware circuit’s function is carries on to the input signal is shifted with multiplying processing, thus achieves in the down link cable transmits the multi-channel program’s goals. Channel multiplying’s principle as shown in Figure 2.
Figure 2 the black block expressed that the user wish looker-in’s program channel the position which locates in the entire program channel, the white rectangle frame expresses the transmission path which and the channel corresponds, the frequency band scope between 950~2150 MHz, abscissa expression frequency space. bank 1~. bank 4 express the high frequency tuner 1~4 group output signals. This processing is divided 2 parts, the signal is shifted with the signal multiplying. Is shifted completes by the SCR chip, the multiplying realizes by the accumulator.
2.2 circuit designs and detail analysis
Figure 3 behind the dashed line dispenses Figure 2 the correspondence.
In the chart 4×4 the matrix is composed in the actual electric circuit by 2 piece of HMC276 chips, uses in choosing opens bank the l~bank 4 some circuit signals, carries on for the SCR chip is shifted processing, SCR is shifted the work to realize under the ST7LNB1 control, each SCR chip’s center frequency is different, with Figure 2 UBO~UB3 center frequency correspondence, this center frequency is by the chip inherent quality decision, often the combination which uses in the identical system has 4 groups combinations and 8 groups combinations and so on, they correspond user band width (UB) respectively is 60 MHz and 40 MHz. These center frequency is definite by the hardware, but in the actual use, is transmits the DISEQC order examination by the set-top box to obtain. In this plan falls a frequency reference diagram 3 point 2 time to realize, first time falls the frequency left side of the dashed line to realize in Figure 3, afterward matrix input signal frequency Freq_martrix_input=|Freq_down_Flo|. Second time falls the frequency right flank the dashed line in SCR to realize in Figure 3, afterward SCR output signal frequency band center frequency Freq_scr_output=F_SCR. What needs to explain, second time falls the frequency to control SCR by ST7LNB1 to realize, refers to SCR the data sheet to be possible to know, SCR may 950~2150 MHz scope random signal frequency deviation to its center frequency nearby bandwidth range, this point transmit by the set-top box the DISEQC order to transmit to ST7LNB1 the related parameter signal to determine, is mainly the local oscillation and the SCR center frequency. Freq_down is the satellite downward signal after narrow filter filter signal carrier frequency, Flo is the high frequency tuner local oscillation frequency. SCR following bandpass filter (BPF) uses in filtering outside the user band width the signal, prevents when the multiplying the signal train circles the distortion. BPF’DI bandwidth and center frequency and each SCR 11 correspondences.
3 software supports
The set-top box software must solve the subject matter including examines the UB number and the center frequency, signal passage’s choice as well as the conflict avoids and so on.
3.1 test the UB number and the UB center frequency
After the hardware equipment disposes, controls overall system’s movement through the software routine. First is transmits DISEQC by the set-top box order examination system UB the integer and the center frequency, the test result reflects hardware’s disposition situation. When the examination process, observes in the signal passage transmits the DISEQC order in circuit’s signal situation and the SCIF signal processing module feedback through the oscilloscope gives the set-top box the signal. The examination method is the oscilloscope turning on down link cable circuit, examines UB by the user operation set-top box transmission the DISEQC order, observes in the circuit the signal situation. Examines result as shown in Figure 4.
In the chart, the spike pulse transmits in the DISEQC order trailing wire cable for the set-top box the signal, may reflect that the SCR center frequency the condition, 4 bandpass scopes after transmitting DISEQC period of time in circuit’s signal, reflected that this electric circuit module to the signal gain situation, is the effective band scope which the signal may exist. After the observation, the above 4 pulse correspondence in 1210 MHz,1420 MHz, l680 MHz,2040 MHz center frequency, produces under the ST7LNBl control. The set-top box system transmits UB_SINGAL_ON () to order to the SCIF module to transmit some data message, reads in some data to ST7LNB1, including SCR center frequency which all possibly exists, altogether 12, when in these frequencies and ST7LNBl save and this hardware circuit related SCR center frequency database match case are fashionable, the ST7LNBl control system in the corresponding frequency transmission feedback signal impulse. After the set-top box catches these signals, may obtain the different SCIF module the inherent frequency spot, simultaneously through the verification should the data sheet obtains the corresponding UB band width. The signal which after the above 4 pass bands are transmit DISEQC to order period of time, the oscilloscope examine, it has reflected the system dialog noise signal gain.
Examines UB the related information solves the key which the subscriber signal circuit chooses. After the UB information examines successfully, the software system through the user interface menu establishment’s related parameter (including information and so on satellite, polarity, local oscillation) transmits the parameter and controls the circuit which to the ST7LNBl selection signal the signal cabin walks. Contrasts physical parameters and so on SCR integer which and center frequency above UB in the test result and the LNB module uses, this system can examine the system-related parameter which normally the UB channel establishes.
3.2 signals as well as signal passage’s choice
User from examination to UB in chooses one, takes the signal finally the frequency band scope which exists in the channel. Also determined to the frequency band (band) choice by the user, including satellite, polar and frequency band height 3 conditions. After above 4 condition determination, various set-top boxes correspondence’s signaling circuit determined. Although various set-top boxes take UB is different, but to elects the satellite, the polarity and the frequency band height have not limited. This information will represent these conditions by the software system by the DISEQC command parameter’s way the message routing for ST7LNB1, is responsible for the DISEQC instruction which by ST7LNBl decodes the indoor set-top box to send out.
After determining the above condition, various set-top boxes may transmit on the respective circuit save in the database the program frequency spot, information and so on data transfer rate, completes to the program information search. This process through examines to single plane’s port select. If chooses good UB, the satellite, polar, the local oscillation combination after in turn, Taiwan operations and so on carries on the program search and trades, the set-top box can the normal work, then indicated that the system may the normal selector channel and completes to the signaling.
3.3 DISEQC order reproduction waiting mechanism
Because various set-top boxes use identical root down link cable transmits the DISEOC signal and the downward feedback signal, and each DISEQC order loads in 22 kHz frequencies carries on the transmission, when in the circuit simultaneously has many set-top box transmissions the DISEQC order, in the line cable’s signal will have the conflict to be unable to recognize. In order to solve this problem, this plan adopts the order reproduction way, the reproduction standby period obtains by the linear feedback shift register, as shown in Figure 5.
When starting, each shift register’s starting value as shown in Figure 5, after that 4 evaluations are the system SCR chip integer binary expressions. When the user trades the Taiwan success, the shift register carries on the shifting function but not to reissue the order. When the system examines has the conflict, system the UB value which takes various set-top boxes (0~7) adds 1 bestows on for shift register latter 4, the first 3 bit data maintain invariable. This time, 7 binary number correspondence decimal digit which constitutes by the shift register with the value which 27 eliminate obtains is the stochastic standby period, the unit for the second. Will dispose the parameter from the set-top box to transmit ST7LNB1, by the ST7LNB1 basis set-top box upload parameter, controls this module to carry on processing to the input signal.
4 subtotals
The system carries on the redesign and the function promotion to the commonly used high frequency tuner electric circuit, enables only to process in 8 group combination group high frequency tuner electric circuits which high frequency/low frequency, the level/vertical, satellite A/B forms, can act according to many users the manual establishment simultaneous working multi-channel signals. On the one hand has multi-channel independent falls the frequency processing electric circuit, on the other hand uses many SCR chips to carry on independently for the multi-channel signals is shifted processing. The signaling frequency which in after the design the process falls the frequency and is shifted processing, obtains in 950~2 150 MHz scopes, will not have the channeling to overlap the disturbance, the multiplexed signal can by the set-top box software and hardware system correctly unmistakably separation and processing. This design commonly used in family many machine and present high-end market popular PVR set-top box. Not only may save the switch component and the line cable, reduces the system the installation cost and to install the difficulty, but can also guarantee when uses the simple root down link cable supports lights program’s processing to various frequencies.
