LMX9838SB National Semiconductor, LMX9838SB Datasheet - Page 14

• Manufacturer Part Number: LMX9838SB
• Manufacturer: National Semiconductor

Specifications of LMX9838SB

• Lead Free Status / Rohs Status: Compliant

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V
I
f
V
DDACT
DD
PPOSC
13.6 TRANSMITTER CIRCUITRY
The transmitter consists of ROM tables, two Digital to Analog
(DA) converters, two low-pass filters, IQ mixers, and a power
amplifier (PA).
The ROM tables generate a digital IQ signal based on the
transmit data. The output of the ROM tables is inserted into
IQ-DA converters and filtered through two low-pass filters.
The two signal components are mixed up to 2.5 GHz by the
TX mixers and added together before being inserted into the
transmit PA.
13.6.1 IQ-DA Converters and TX Mixers
The ROM output signals drive an I- and a Q-DA converter.
Two Butterworth low-pass filters filter the DA output signals.
The 6 MHz clock for the DA converters and the logic circuitry
around the ROM tables are derived from the autotuner.
The TX mixers mix the balanced I- and Q-signals up to 2.4-2.5
GHz. The output signals of the I- and Q-mixers are summed.
13.7 32 kHz Oscillator
An oscillator is provided (see Figure 4) that is tuned to provide
optimum performance and low-power consumption while op-
Symbol
Supply Voltage
Supply Current (Active)
Nominal Output Frequency
Oscillating Amplitude
Duty Cycle
Parameter
TABLE 10. 32.768 kHz Oscillator Specifications
14
erating with a 32.768 kHz crystal. An external crystal clock
network is required between the 32k+ clock input (pad 27) and
the 32k- clock output (pad 28) signals.The oscillator is built in
a Pierce configuration and uses two external capacitors. Ta-
ble 10 provides the oscillator’s specifications.
In case the 32kHz is not used, it is recommended to leave
32k- open and connect 32k+ to GND.
Condition
FIGURE 4. 32.768 kHz Oscillator
1.62
40
Min
1.8
2
32.768
1.8
-
Typ
1.98
60
Max
30027903
V
µA
kHz
V
%
Unit