Document
U3550BM
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Low-Power FM Transmitter / Synthesizer System 26 to 50 MHz
Description
The U3550BM is a radio-frequency IC for analog cordless telephone applications in the 26/50-MHz band (CTO standard). The IC performs full duplex communication. The transmitting and receiving frequency depends on whether the IC is used in the handset or in the base station. The U3550BM’s frequency converter consists of an FM transmitter with switchable output power and receiver Mixer 1 in the same unit. A two-wire bus interface can be used for frequency control as well as for switching the transmitter’s power amplifier and the receiver. Fine frequency adjustment of the reference crystal oscillator is programmable. The receive part is designed for a double-conversion architecture. The incoming radio-frequency signal will be filtered and amplified before reaching the first mixer. At this stage, the RF signal will be converted down to the first intermediate frequency (10.7 MHz) by using a local adjustable oscillator (VCO3). The frequency of this oscillator is controlled by the PLL. The transmitter part contains two PLL-controlled VCOs. The frequency modulation is accomplished by superposing the incoming audio signal on the first PLL control voltage. In this system, the frequency is a product of mixing VCO1 with local oscillator (VCO3). The FMmodulated carrier is amplified by external power amplifier before entering the output filter and the antenna connector.
Features
D All PLLs and most of the oscillators are integrated D All functions and channel selection controllable by D D D D
serial bus Receiver Mixer 1 with integrated image rejection Up to 25 channels selectable depending on CT0 standard Integrated oscillator circuit with external crystal (11.15 MHz) Programmable carrier-modulation frequency
VBAT DELVB DELGND MIXO Mixer 1 + 45 – 45 sin LOGND
Application
Block Diagram
VCC
om po ne
systems
PCLO 10.7 MHz cos 2 N Phase comparator cos D1 D2 Loop filter Phase comparator AGND VSS MODIN
D CT0 (USA, France, Spain, Netherlands, Portugal,
Korea, Taiwan, New Zealand, China)
D Narrowband voice and data transmitting / receiving
nt s
OSCVDD K 20 557.5 KHz VCO 1 2
Ad ro nic C
MIXIN
MIXVB
LO1 LO2
VCO 3
sin
Mixer 2 + 45 – 45
VTX
RFOVB RFO
VCO 2
RFOGND
Figure 1. Block diagram
Rev. A2, 10-Sep-98
Gm bH
MCKA OSCGND XCK MCKO 11.15 MHz Oscillator interface Serial BUS interface C D D3 P GREF Phase comparator LFGND MLF
13280
1 (25)
Preliminary Information
U3550BM
www.DataSheet4U.com Pin Description
MCKO 1 D C OSCGND 2 3 4
28 VCC 27 VSS 26 MCKA 25 MODIN 24 LFGND 23 MLF 22 VBAT 21 AGND 20 VTX 19 RFOVB 18 RFO
XCK 5 OSCVDD 6 DELVB 7 DELGND 8 GREF 9
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
MIXIN 10 MIXVB 11 MIXO 12 LO1 13 LO2 14
11623
17 RFOGND 16 LOGND 15 PCLO
Figure 2. Pinning
Order Information
Extended Type Number U3550BM-AFL U3550BM-AFLG3
Ad ro nic C
om po ne
Package SO28 SO28
nt s
Taped and reeled
2 (25)
Preliminary Information
Gm bH
Remarks
Pin 1 2 3 4 5 6 7
Function Clock output for peripherals Data input of serial bus Clock line of serial bus Oscillator ground Oscillator input (11.15 MHz) Oscillator supply input Phase correction VCO3 supply input DELGND Phase correction VCO3 ground GREF Voltage reference for internal current sources MIXIN Mixer input MIXVB Mixer-supply input MIXO Mixer output LO1 Tank elements for LO are connected to these pins LO2 PCLO Phase comparator PLL3 output LOGND VCO3 ground RFOGND RF transmit output ground RFO RF transmit output RFOVB Power-supply input of RF transmit output buffer VTX Power-supply output of RF external power amplifier AGND Analog ground VBAT Power supply of analog part MLF Modulator loop filter LFGND Modulator loop-filter ground MODIN Modulator input signal MCKA Peripheral-clock output adjustment VSS Digital ground VCC Power supply of digital part
Symbol MCKO D C OSCGND XCK OSCVDD DELVB
Rev. A2, 10-Sep-98
U3550BM
www.DataSheet4U.com
VCO Adjustments
To be able to use a wide VCO frequency range (i.e., VCO2 = 26.3 to 49.9 MHz), VCO1 and VCO2 have a rough adjust and a fine adjust to increase the frequency range given by the phase comparator. The 4 rough adjusts for VCO1 and VCO2 (3 used in VCO1) are correlated to the country setting. For each country, there are two sets of VCO rough adjust settings, one for the base and one for the handset (see tables Channel Frequencies, Dividers and Country Settings). To achieve the adaption to the various country standards, there is a fine adjust with 32 steps for VCO1 and VCO2. These fine adjusts can be set manually (for test purposes) or by the automatically mode. Theoretically, the indicator of the change (increase/ decrease when the voltage of the phase comparator is too high) is selectable. The programming value ‘1’, however, is necessary. Setting normal conditions VCO1: EAFA1 = 1, automatic fine adjust VCO1 enabled SAFA1 = 1, sign of auto fine adjustment VCO1 = 1. Setting for VCO2 i.