Nokia 6620 Service Manual 07 nhl12 RF

Nokia Customer Care

NHL-12 Series Transceivers

7 - RF Description &

Troubleshooting

Issue 2 10/2004 COMPANY CONFIDENTIAL

NHL-12

Nokia Customer Care 7 - RF Description & Troubleshooting

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RF Description and Troubleshooting................................................................ 4

RF key component placement ........................................................................... 4

RF measurement points..................................................................................... 5

Test points ....................................................................................................... 7

RF Implementation in NHL-12............................................................................8

RF frequency plan.............................................................................................. 8

RF power supply configuration ........................................................................ 10

Introduction to RF troubleshooting................................................................. 11

Receiver Description and Troubleshooting.................................................... 12

Receiver........................................................................................................... 12

Rx front-end..................................................................................................... 12

General instructions for Rx troubleshooting..................................................... 14

Troubleshooting charts for receiver ................................................................. 15

Troubleshooting diagram for GSM850 receiver .............................................15

Troubleshooting diagram for GSM1900 receiver ...........................................17

Transmitter Description and Troubleshooting...............................................21

Transmitter characteristics............................................................................... 21

Power amplifier................................................................................................ 21

RF ASIC Helgo ................................................................................................ 22

AFC function.................................................................................................... 22

General instructions for Tx troubleshooting ..................................................... 23

Transmitter troubleshooting diagram ............................................................. 24

Pictures of transmitter signals ........................................................................27

Additional Information on EDGE Troubleshooting........................................ 30

Pictures of EDGE transmitter signals .............................................................34

Synthesizer Description and Troubleshooting .............................................. 37

Frequency synthesizers................................................................................... 37

General instructions for synthesizer troubleshooting....................................... 40

Troubleshooting chart for PLL synthesizer ....................................................41

Frequency lists................................................................................................. 43

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NHL-12 7 - RF Description & Troubleshooting Nokia Customer Care

1. RF Description and Troubleshooting

The RF module performs the necessary high frequency operations of the GSM850/1800/1900 tripleband (EDGE) engine. Both the transmitter and receiver have been implemented by using direct conversion architecture which means that the modulator and demodulator operate at the channel frequency.

The core of the RF is an application-specific integrated circuit, Helgo. Another core component is a power amplifier module which includes two amplifier chains, one for GSM85 0 and the other for GSM1800/1900.

Other key components include:

• 26 MHz VCTCXO for frequency reference

• 3290-3980 MHz SHF VCO (super high frequency voltage controlled oscillator)

• Antenna switch module

• Four SAW filters

• Three transformer baluns

■ RF key component placement

Figure 1:RF key components

The control information for the RF is coming from the baseband section of the engine through a serial bus, referred later on as RFBus. This serial bus is used to pass the information about the frequency band, mode of operation, and synthesizer channel for the RF. In addition, exact timing information and receiver gain settings are transferred th rough the RFBus. Physically, the bus is located between the baseband ASIC called UPP and Helgo.

Using the information obtained from the UPP, Helgo controls itself to the required mode of o peration and further sends control signals to the front end and power amplifier modules. In addition to the RFBus, there are still other interface signals for the power control loop and VCTCXO control and for the modulated waveforms.

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Nokia Customer Care 7 - RF Description & Troubleshooting

RF circuitry is located on one side of the 8-layer PWB. The possible EMC leakage is prevented by using metal cans. The RF circuits are separated

into three blocks:

• PA, antenna switch module, Rx 1900 LNA, Rx 1900 SAW filter, Rx 1900 transformer balun, Tx 1800/1900 transformer balun and Tx 850 SAW filter

• Helgo RF IC, VCTCXO, Rx 850 SAW filter and Rx 1800 SAW filter

• VCO and transformer balun for VCO The RF transmission lines constitute of striplines and microstriplines after PA. The baseband circuitry is located on one side of the board, which is shielded with a metallized

frame and ground plane of the UI board.

■ RF measurement points

Figure 2: RF measurement points - Bottom

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Figure 3: RF measurement points - Top

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Nokia Customer Care 7 - RF Description & Troubleshooting

Test points

Table 1: Test points

Signal name Reference Signal name Reference

VBAT C7020 To Antenna J7100 VR1 C7306 VANT 1 C7102 VR2 C7326 VANT 2 C7101 VR3 C7201 VANT 3 C7100 VR4 C7303 RFBusEna1X R7302 VR5 C7304 RFBusData R7302 VR6 C7302 RFBusClk R7302 VR7 C2230 RESET R7302 VrefRF01 C7311 VCTCXO G7200 RFTemp C2226 Clk to BB C2902 VCO out G7201 RFout 1800/1900 Z7100 VCO VCC C7205 TXA C7313 AFC R7200 TXC C7314 RXI J7301 TXP J7303 RXQ J7300 Mode R7002 ASM out 850RX L7100/L7101 VPECTRL3 (ALC) C7329 ASM out 1800RX L7102/L7103 Iref 850 (IPA1) R7001 ASM out 1900RX C7112/C7113 Iref 1800/1900 (IPA2) R7000 LNA VCC C7109 VTXB 850 C7013 LNA P R7202 VTXB 1800/1900 C7014 TXIP / TXIN R7305 VPCTRL 850 R7003 TXQP / TXQN R7306 VPCTRL 1800/1900 R7007 PA in 850 R7005 PA in 1800/1900 L7003 RFout 850 L7004 VTXLO 850 C7320

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2. RF Implementation in NHL-12

■ RF frequency plan

RF frequency plan is shown below. The VCO operates at the channel frequency multiplied by two or four depending on the frequency band of operation. This means that the baseband modulated signals are directly converted up to the transmission frequency and the received RF signals directly down to the baseband frequency.

Figure 4:RF Frequency plan

HELGO

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RF block diagram NHL-12

Figure 5:RF Block diagram

Helgo

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■ RF power supply configuration

Figure 6:Power distribution diagram

HELGO

LNA GSM1800/ 1900

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Nokia Customer Care 7 - RF Description & Troubleshooting

3. Introduction to RF troubleshooting

All measurements must be done using a spectrum analyzer with a high-frequency high-impe dance passive probe (LO-/reference frequencies and RF power levels) and an oscilloscope with a 10:1 probe (DC-voltages and low frequency signals).

The RF section is build around one RF ASIC (HELGO N7300). Before changing HELGO, please check the following things: supply voltages and serial communication coming from baseband to HELGO are both OK.

Apart from key components described in this document here are a lot of discrete components (resistors, inductors and capacitors) which troubleshooting is done by checking if soldering of the component is done properly (for factory repairs checking if it is missing from the PWB). Capacitor can be checked for shortening and resistors for value by means of an ohmmeter, but be aware that in-circuit measurements should be evaluated carefully.

Please be aware that all measured voltages or RF levels in this document are rough figures. Especially RF levels vary due to different measuring equipment or different grounding of the used probe. When using the RF probe, use metallic tweezers to connect the probe ground to the PWB ground as close to the measurement point as possible.

Please note that the grounding of the PA module is directly below PA module, therefore it is difficult to check or change. Most RF semiconductors are static discharge se nsitive! ESD protection must be taken care of during repair (ground straps and ESD soldering irons). HELGO and PA are moisture sensitive which means that parts must be pre-baked prior to soldering.

For easier troubleshooting, this RF troubleshooting document is divided into sections.

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4. Receiver Description and Troubleshooting

■ Receiver

Each receiver path is a direct conversion linear receiver. From the antenna, the received RF signal is fed to a front end module where a diplexer first divides the signal into three separate paths according to the band of operation: either lower GSM850 or upper GSM1800 or GSM1900 path.

Most of the receiver circuitry is included in Helgo.

■ Rx front-end

The front-end features include:

• Antenna 50 ohm input

• Rx GSM850, GSM1800 and GSM 1900 50 ohms inputs

• Txs single 50 ohm input

• 3 control lines from the Helgo

Figure 7: Front-end

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Nokia Customer Care 7 - RF Description & Troubleshooting

Receiver characteristics

Item Values, GSM850/1800/1900

Type Direct conversion, Linear, FDMA/TDMA LO frequencies 3476...3576 MHz / 3610...3760 MHz/

3860...3980 MHz Typical 3 dB bandwidth +/- 91 kHz Sensitivity min. - 102 dBm (normal condition) Total typical receiver voltage gain (from

antenna to Rx ADC) Receiver output level (RF level -95 dBm) 230 mVpp, single-ended I/Q signals to Rx

Typical AGC dynamic range 83 dB Accurate AGC control range 60 dB Typical AGC step in LNA 30 dB GSM1800/1900 25 dB GSM850 Usable input dynamic range -102... -10 dBm RSSI dynamic range -110... -48 dBm Compensated gain variation in receiving band +/- 1.0 dB

86 dB

ADCs

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