Motorola A920 - Page 77

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A920: TX Modulator (MAX2363)

Description

The in phase (I) and quadrature phase (Q) inputs are received at pins #23 (Q+), #24(Q-), #25(I+), & #26(I-) of U200. The expected DC bias levels are 1.30V - 1.40V

with a minimum 300mVpp signal upon the DC level.

The MAX2363 receives the differential I/Q BaseBand input and converts it up to the IF frequency of 380MHz through a quadrature modulator and IF variable gain

amplifier (VGA). The IFINH+ (pin #10) and IFINH- (pin #11) input are connected through off-chip FL201 from IFOUT+ (pin #17) and IFOUT- (pin #16), respectively.

The function of FL201 is to provide image rejection and out-of-band interferers filtering. The frequency conversion process performed by the mixer / oscillator combina-

tion sometimes will allow a frequency other than desired frequency to be fed into the IF and subsequently amplified. The SAW filter (FL201) has a nominal center fre-

quency of 380MHz and an insertion loss of ~ 3.5dB with a total bandwidth of 5MHz.

The IF and RF VGA (VGC1) are common and allow for varying the IF / RF output level . HARMONY_LITE controls the VGC signal with a range of ~1.3 - 2.6V and

provides gain a control range of ~75dB.

The MAX2363 VCO output frequency is controlled by an internal phase lock loop (PLL) synthesizer. The external loop filter consists of the components connected to

pins #33 and #32 (& pin #38). The VCO output frequency (TankH+ / TankH-) at pin #33and pin #32 are divided down internally, to a desired comparison frequency.

The reference signal at pin #36 (REF_FREQ) is also divided down to the same comparison frequency. The two divided signals are then compared with a three state digi-

tal phase detector. The internal phase detector drives the charge pump as well as the lock-detect logic(2361_LOCK). The charge pump output (IFCP, pin # 38) is pro-

cessed by the external loop filter and drives the tunable resonant network, altering the VCO frequency (760MHz) and closing the loop.

The differential IF output at pins #17 & #16 (IFOUTH+ / IFOUTH-) support high IF operation of frequency of 380MHz. The signal is routed to an off-chip IF SAW filter

(FL201) and up-mixed to RF through an image reject mixer and RF VGA. The signal is further amplified with an on-chip PA driver. The RF signal is then routed to an

interstage RF SAW filter (FL401).

The IF synthesizer (760 MHz VCO) and local oscillator (RF_LO) buffer are both programmable through the 3-wire bus. The sequence manager from HARMONY_LITE

programs standby mode(TX_STBY*) and shutdown mode(2361_SHDN). This IC operates from a pair of supply voltages VCC_DIG (isolated supply for IF_CP and 760

VCO) & VCC_ANA derived from VRF_TX_2_775V.

Motorola Confidential Proprietary

4-28

380 MHz

Offset

Synthesizer

MAX2363

U200

IF PLL

IF SAW

FL201

TX SAW