Motorola C1002 Instructions d'exploitation télécharger pdf (Page 56)

100

101

9-6 Frequency Generation Circuitry

The Frequency Generating Unit is centered on one main IC, Trident (U001). The modulation data is

sent to the synthesizer through 3 TX SSI lines. The block diagram illustrates the interconnect and

support circuitry used in the Frequency Generating Unit. Refer to the relevant schematics for the

reference designators.

The synthesizer is powered from 2.8V ANA, 2.8V DIG, 1.875V DIG and 5V ANA supplied from

U3000-1. The synthesizer in turns generates a superfiltered 4.5V which powers up the 800MHz &

900MHz VCO while a cascaded buffer is powered by 5V VBUS2.

In addition to the VCO, the synthesizer interfaces with the microcontroller. Programming of the

synthesizer is accomplished through the 4 lines; SPI_MISO, THK_CE, SPI_MOSI and SPI_CLK via

pin D10, D8, D9 and D11 respectively. A 1.875V dc signal from the synthesizer lock detect line

indicates to the microprocessor that the synthesizer is locked.

U001 has dual port modulation capability. The microprocessor supplies low port and high port words

to pin F11 of U001. For high port modulation, the audio runs through an internal attenuator for

modulation balancing purpose before it goes out to the loop filter via pin L9. For the low port

modulation, the audio is fed into the main synthesizer, where it is summed with the main_num

channel frequency word, then supplied to the accumulator of the Fractional-N synthesizer before

going out to the VCO.

3.1 Synthesizer

U001 uses a 16.8 MHz crystal (Y001) to provide a reference for the system. Together with R001,

R002, C010, C011, C012 and C043, they build up the reference oscillator which is capable of 0.5ppm

stability over temperature of -30ºC to 85 ºC. It also provides 16.8MHz at pin J11 of U001 to be used by

ABACUS. The loop filter which consists of R007, R008, R009, C021, C023, C024, C025, C026, C027

and C028 provides the necessary dc steering voltage for the VCO and determines the amount of

noise and spur passing through.

For achieving fast locking for the synthesizer, an internal adapt charge pump provides higher current

(~10mA) at pin G2. The required frequency is then locked by normal mode charge pump at pin G3.

Both normal and adapt charge pumps get 12V supply from the voltage multiplier circuit that consists

of D002, D003, C031, C032, C033, C034, C035 and C036.

3.2 VCO - Voltage Controlled Oscillator

Each VCO in conjunction with the synthesizer generates RF injection signal for both receive and

transmit modes of operation. The 800MHz VCO comprises of a Colpitts oscillator built around Q203.

Vcontrol is supplied to back-to-back varactors (D200 and D201). The LC tank comprises of C207 and

L202. Similarly in 900MHz VCO which is also a Colpitts oscillator built around Q204 with LC tank,

C222 and L208. Vcontrol is supplied to back-to-back varactors (D204 and D205). Both oscillators are

supplied with a 4.5V super-filtered supply from the synthesizer, U001 through a RF switch that

consists of Q200, Q201, C200, C201, C202 and C203.

A common cascaded buffer, built up of a buffer IC, U200 cascaded with a discrete transistor built

around Q205 with a switched attenuator at input of buffer IC is supplied with a 5V ANA supply from

MAKO, U3000-1. A switchable attenuator is placed at the input of the Buffer IC. In the Tx mode the

input power to the IC is reduced by turning on the switchable attenuator implemented, with a PIN

diode D202. The receiver mixer requires a higher injection power than than the transmitter. A lower

transmit power improves isolation between VCO and transmitter amplifiers. The output of the

cascaded buffer is matched to 50Ohms by C246, C247, C248, L217 and L218 then switched between

RX and TX through an RF switch i.e. U201 providing output power level of 6dBm to RX_1ST_LO_INJ

and output power level of 3dBm to TX_BUFF.

1 2 ... 51 52 53 54 55 56 57 58 59 60 61 ... 100 101

Commentaires sur ces manuels

Pas de commentaire

Motorola C1002 Instructions d'exploitation Page 56

Commentaires sur ces manuels

Produits connexes et manuels pour Téléphones Motorola C1002