cxa3003r Sony Electronics, cxa3003r Datasheet - Page 28

• Manufacturer Part Number: cxa3003r
• Description: Baseband Analog Processing Ic For Dual-mode Cdma/fm Cellular Phone
• Manufacturer: Sony Electronics

6. Transmit VCO Phase Detector
7. FM Modulation Scaling
The phase detector output, PD OUT, is the output of a dual mode bi-directional charge pump. It provides
two levels of output current for frequency acquisition (±175 µA) and phase lock maintenance (±16 µA)
after the VCO frequency is at or near its final frequency. The phase detector also provides a lock detect
output, LOCK. This signal is low when unlocked, and high (high-impedance) when unused or in IDLE or
SLEEP Modes. LOCK will indicate the unlocked condition until the VCO frequency is at its final value.
LOCK will then toggle until phase lock has been established.
The current available from PD OUT is set by an external resistor connected between PD ISET and
ground (shown in Fig. 12). The value of the PD ISET resistor is determined by
Where Io is the current available for maintaining the transmit VCO frequency. During acquisition of the IF
frequency, the current limit from PD OUT increases to 11 times that set by the resistor on PD ISET. A
recommended Io of 16.3 µA results in R
The FMMOD output is used to frequency modulate the transmit VCO. The output voltage swing on FM
MOD is normally 550 mVp-p. This modulating voltage must be scaled to achieve the required frequency
deviation of the transmit VCO frequency when the CXA3003R is operating in FM mode. A ±30 kHz
deviation of the transmit VCO frequency translates into a ±15 kHz deviation of the transmit IF frequency.
A simple resistive voltage divider may be used as long as the total load on FM MOD is greater than 10
k . The output of the voltage divider drives the anode side of the varactor diodes (shown in Fig. 12).
PD OUT
LO
Reference
Divider
Phase
Detector
n=16
VCO
R
Fig. 14 Transmit VCO synthesizer
PD
= 0.64/I
PD
=39 k ±1 %.
O
—28—
19.68MHz from TCXO
Divider
1/2
Divider
1/106
to TX Modulator
CXA3003R