Functional Description Receiver

The antenna switch/connector connects an antenna or a cable to the PCB. Fixed to the PC Card mechanics, the connector's function is also to launch the received signal from antenna to the microstrip environment on PCB. The microstrip takes the received signal first to the duplex filter, that passes the signal to the receive (RX) arm of the transceiver. Another function of the duplex filter is to reject the RF spectrum outside the RX band.

The signal is then amplified by a low noise preamplifier. The performance of the amplifier determines to a large extent the sensitivity of the receiver. LNA gain is controlled by the automatic gain control (AGC) signal PDATA0 which is received from the BB (MAD). The nominal gain of the LNA is 20 dB. The gain can be crudely reduced by 40 dB in strong field conditions, by setting PDATA0 to logic low (zero) instead of logic high (3 V).

Proceeding the preamplification, the signal is filtered by an RF RX filter. The filter rejects spurious signals outside the RX band that are coming from the antenna and spurious emissions coming from the receiver itself.

Next, the filtered signal is down converted by the RF mixer to the first intermediate frequency (IF) of 71 MHz. The first local oscillator (LO) sine wave is generated in the synthesizer. The first-LO frequency alone determines which RF carrier is selected from the RX band, down converted and passed on to the next stages of the receiver.

The IF amplifier, which is again a discrete circuit, amplifies the down-converted 1st-IF signal by another 20 dB and passes the signal on to the 1st-IF RX filter. This amplification is needed to compensate for the conversion loss of the RF mixer and to drive up the signal level for the following filter and mixers stages.

The 1st-IF filter constitutes the channel selectivity element of the receiver. It rejects adjacent channel signals (except the 2nd adjacent). It also rejects the blocking signals and the 2nd image frequency.

After filtering, the IF signal is fed to the receiver part of the CRFRT IC. In the CRFRT, the signal is first applied to an AGC amplifier, the gain of which is adjusted by the TXC-signal. After another fixed gain amplifier stage, the received signal goes to the 2nd-IF mixer. A sine wave at 58 MHz for the second down conversion is obtained by dividing the synthesizer output at 232 MHz twice in the dividers of the CRFRT. Thus, the 2nd IF is (71 - 58) MHz = 13 MHz.

After the second down conversion, the signal is filtered by an off chip 13-MHz filter, which constitutes the channel selectivity element of the receiver. The signal is then fed back to the CRFRT for amplification and amplified by a differential amplifier of the CRFRT.

Finally, the 13-MHz signal is fed differentially through an attenuator circuit to the baseband part of the transceiver where it is received by RFI2 (RF interface circuit).

Technical Documentation System Module

Synthesizer

A crystal oscillator generates a highly stable 13-MHz clipped sine-wave signal that is used as the frequency reference for the synthesizer and also as the baseband reference clock (RFC signal). The input to the crystal oscillator is the AFC (automatic frequency correction) signal that keeps the oscillators frequency locked to the reference frequency of cellular network. The RF section receives the AFC signal from BB (RFI2).

A UHF VCO (ultra high frequency voltage controlled oscillator) generates a sine-wave at precise frequency that may vary from 1006.0 to 1031.0 MHz. The output of the UHF VCO is used for the first down conversion of received signals and for the final up conversion of transmitted signals. Once the UHF sine wave has been generated in the UHF VCO, it is then applied to the UHF buffer. The buffer reduces frequency pulling of the UHF VCO against changing impedances in the RF mixers LO port. It also amplifies the UHF sine wave level.

VHF VCO (very high frequency voltage controlled oscillator) generates a 232-MHz sine wave, that is used in CRFRT for the TX I/Q modulation and for the down converting RX signals to the 2nd IF. It incorporates a buffer that reduces frequency pulling and amplifies the VHF output.

Transmitter

RFI2 feeds the differential in-phase (I) and quadrature (Q) signals to the I/ Q-modulator of the CRFRT. The I/Q modulator modulates a 116-MHz sine wave with the I and Q signals. The 116-MHz sine wave is obtained by dividing the synthesized 232-MHz by two. The modulated TX IF signal at 116 MHz is amplified by an AGC amplifier which is also implemented on CRFRT. In this application the gain of the AGC amplifier has been set to fixed maximum level, because the power control has been implemented to the power amplifier.

The final radio transmit signal is generated by mixing the UHF VCO sine wave and the modulated TX IF signal in the RF mixer. The input signal is a modulated 116-MHz signal coming from the quadrature modulator (part of the CRFRT circuit). The LO is filtered from TX signal by using a microstrip trap.

After mixing, the slightly filtered TX signal is amplified in the PA-driver amplifier to the level of +5 dBm, level required by the power amplifier.

The TX filter rejects the spurious signals generated in the up conversion mixer. It also rejects the local and IF signal leakages as well as broad band noise.

The power amplifier (PA) amplifies the TX signal to the desired power power level which may vary by 28 dB (GSM Phase 2). The maximum output level of the PA is typically 31.5 dBm (1.41 W).

The power control loop controls the output level of the power amplifier. The transmitter uses a directional coupler and a power detector for monitoring and adjusting the TX power. The difference between the power control signal (TXC, generated by RFI2) and the detected voltage is amplified and used as a control voltage for the power amplifier.

System Module Technical Documentation

The duplex filter forwards the transmit signal to the antenna connector and rejects amplified noise at RX band as well as harmonic products of the TX signal.

The power amplifier amplifies the TX signal level high enough so that the lossy passive circuits that follow the PA do not attenuate signal below desired antenna power. In other words, the PA must provide enough power to compensate for the losses in the directional coupler, duplex filter, antenna, and antenna connector. The highest available power from the antenna connector of this module, suited for GSM Class 5, is 0.8 W.

Transmitter Power Budget. From PA to Antenna

Item

Normal conditions

Extreme conditions

Unit / Notes

Output power of the PA

31.5

30.0

dBm

Loss of directional coupler

0.4

0.5

dB

Loss of duplex filter

1.8

2.0

dB

Loss of antenna connector

0.3

0.4

dB

Loss of antenna

0

0

dB

Radiated power to free space

29.0

27.1

dBm

Technical Documentation System Module

Block Diagram of GX8 RF section m

Nokia Nhx 2nd Schematic Diagram

RPE-1

PAMS

System Module

Technical Documentation

RF Characteristics

Receiver

Item

Values

RX frequency range

935... 960 MHz

Type

Linear, two IFs

Intermediate frequencies

71 MHz, 13 MHz

3 dB bandwidth

± 100 kHz

Reference noise bandwidth

270 kHz

Sensitivity

-102 dBm, S/N > 8 dB, BN=135 kHz

AGC dynamic range

94 dB, typ.

Receiver gain

65 dB (voltage gain)

RF front end gain control range

40 dB

2nd-IF gain control range

57 dB

Input dynamic range

-102 ... -10 dBm

Gain relative accuracy in receiving band

+/- 1.5 dB

Gain relative accuracy on channel

+/- 0.4 dB

Duplex filter

The duplex filter is a module that consists of hermetically packaged SAW resonators and some discrete matching components on a glass epoxy (FR4) carrier. The module is covered by a metal lid. (part code 4510113).

Parameter

Transmitter

Receiver

Center frequency

ft: 902.5 MHz

fr: 947.5 MHz

Pass band width (BW)

ft +/- 12.5 MHz

fr +/- 12.5 MHz

Insertion loss at BW

1.8 dB max

3.9 dB max.

Ripple at BW

1.0 dB max.

1.3 dB max.

Terminating impedance

50 ohms

50 ohms

VSWR at BW

1.8 max.

1.8 max.

Attenuation

Freq. (MHz)

Att. (dB)

Freq. (MHz)

Att. (dB)

935 ... 960

20 min.

DC ... 800

35 min.

1780 ... 1880

30 min.

890 ... 915

25 min.

2640 ... 2745

30 min.

980 ... 1050

20 min.

3560 ... 3660

30 min.

1070 ... 1100

30 min.

1100 ... 2000

25 min.

2000 ... 3500

20 min.

Permissible input power

4.0 W max 2.0 W avg.

Terminating impedance

50 ohm

Temperature

-30...+80°C

Mechanical dimensions

12.7 x 8.2 x 1.8 mm3 max

Technical Documentation System Module

Low noise amplifier

The low noise amplifier consists of a low noise NPN Si bipolar junction transistor (BJT), discrete passive components, and microstrip line elements. There is also a switch transistor pair for PDATA0 signal. (part code 4210074).

Parameter

Minimum

Typical / Nominal

Maximum

Unit / Notes

Frequency band

935...960

MHz

Supply voltage

2.7

3.0

3.6

V

Current consumption

8

mA

Insertion gain

18

20

dB

Noise figure

2.0

dB

Reverse isolation

15

dB

Gain reduction (PDATA0=1)

40

dB

IIP3

-10

dBm

Input VSWR (Zo=50 ohms)

2.0

Output VSWR (Zo=50 ohms)

2.0

The RF RX filter is a SAW filter. It rejects spurious and blocking signals coming from the antenna. It also rejects the local oscillator leakage towards the antenna. (part code 4510065.)

Parameter

Minimum

Typical / Nominal

Maximum

Unit / Notes

Terminating impedance

50

ohms

Operating temperature range

-25

+80

deg. C

Center frequency (fo)

947.5

MHz

Bandwidth (BW)

+/- 12.5

MHz

Insertion loss at BW

4.0

dB

Ripple at BW

1.5

dB

Return loss at BW

10.0

dB

Attenuation DC ... 890 MHz

35.0

dB

Attenuation 890 ... 915 MHz

20.0

dB

Attenuation 980 ... 1025 MHz

15.0

dB

Attenuation 1025 ... 1500 MHz

35.0

dB

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