Panasonic EB-GD90 Technical Manual

Also see for EB-GD90: Operating instructions

Contents

http://cxema.ruRECEIVERIssue A Section 5 MCUK990801G8Revision 0 – 22 – Technical Guide5.2 Functional DescriptionThe main building block for the Dual Band Receiver is the Hitachi Bright2 IC. The receiver is a double superhet type with the1st IF at 225 MHz and 2nd IF at 45 MHz. The intermediate frequencies are common to both frequency bands.The Rx IC contains the following stages:1. Gain controlled 1st mixer for GSM 900 band.2. Gain controlled 1st mixer for GSM 1800 band.3. Gain controlled 2nd mixer.4. Gain controlled IF amplifier5. I,Q quadrature down converter.6. Baseband Op Amps for further amplification and some filtering of the baseband I,Q signals.5.2.1 Dual Band ReceiverFigure 5.1: Dual Band ReceiverRF input to the receiver is either via the antenna or via the H/F RF connector for test purposes. The input signal from theantenna or the H/F RF connector is fed into the GSM 900/GSM 1800 dual band LNA MMIC via the Diplexer port, Tx/Rxswitches to the dual band Rx SAW filter. The diplexer band splits the two GSM frequency bands whilst the pin switches routethe signal flow from the receiver and the transmitter as required. The receiver 1st SAW filter provides the roofing filter for theRx front end.The dual band LNA gain is constant, typically 18 dB for GSM 900 and 17dB for GSM 1800. Noise factor is typically 1.5dB forboth bands. Operation of the dual band LNA is controlled directly by the PCNnGSM band switch signal.The output from the LNA passes through a dual BP SAW filter and is then fed into the 1st mixer for each band. Both mixersare controlled by a 3-wire bus, typically providing between +9.5dB and -2dB gain for GSM900, and between +8.5dB and -3.5dBfor GSM 1800.The IF output at 225 MHz from the 1st mixer is filtered by the differential IF SAW filter before it is fed into the 2nd mixer. Theuse of differential filters eliminates the need for baluns and provides some cost and space advantage. The 2nd mixer is alsogain controlled from a 3-wire bus, typically between +13dB and -3.0dB. Gain switching is synchronised with the 1st mixer.Output from the 2nd mixer at 45 MHz is filtered by an L-C network before it is fed to the gain controlled IF amplifiers.The IFamplifier is gain controlled by a three-wire bus from -29 to +69 dB in 2 dB steps. This function is used for AGC purposes.The output from IF amplifiers is fed into two quadrature mixers where it is converted down to baseband. The IF LO is generatedat 540 MHz by an external discrete VCO module. An on-chip divider on the Rx IC divides this six and then by two. It alsoproduces two outputs in quadrature to generate the baseband I and Q signals. The outputs from the mixers are connected toexternal pins through a pair of buffers. Two on-chip Op Amps are used to amplify the AC signal from the mixers to meet theoverall signal performance requirements.The DC level at the output of the Op Amps is 1.35 V with a 200 mV p-p single ended AC swing controlled by the AGC loop tomaintain optimum receiver performance.GSM 900DUALLNAU203PGCGSM 1800 1800DUAL RXSAWFL203DUAL BAND RECEIVER (PART)U101FL200IFSAW1stMixer2ndMixer9001800900LPF RxTxRxTxExtAnt.HPF10085-1S101DUAL RxSAWFL201DIPLEXERIQDemodulator