LMX9820ASMX/NOPB National Semiconductor, LMX9820ASMX/NOPB Datasheet - Page 18

• Manufacturer Part Number: LMX9820ASMX/NOPB
• Description: MODULE BLUETOOTH SERIAL PORT SMD
• Manufacturer: National Semiconductor

Specifications of LMX9820ASMX/NOPB

• Frequency: 2.4GHz
• Data Rate - Maximum: 704kbps
• Modulation Or Protocol: Bluetooth v1.1, Class 2
• Applications: PDA's, POS Terminals
• Power - Output: 1dBm
• Sensitivity: -81dBm
• Voltage - Supply: 2.85 V ~ 3.6 V
• Current - Receiving: 65mA
• Current - Transmitting: 68mA
• Data Interface: PCB, Surface Mount
• Memory Size: 256Kb Flash
• Antenna Connector: PCB, Surface Mount
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 116-LTCC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMX9820ASMX; LMX9820ASMXTR

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8.0 Digital Smart Radio
8.6 TRANSMITTER CIRCUITRY
The transmitter consists of ROM tables, two Digital to Ana-
log (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.
8.6.1 IQ-DA Converters and TX Mixers
The ROM output signals drive an I- and Q-DA converter.
Two Butterworth low-pass filters filter the DA output signals.
The 6 MHz clock for the DA converters and the logic circuit-
ry 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.
8.7 CRYSTAL REQUIREMENTS
The LMX9820A includes a crystal driver circuit. This circuit
operates with an external crystal and capacitors to form an
oscillator. Figure 9 shows the recommended crystal circuit.
Table 24 on page 22 specifies system clock requirements.
The RF local oscillator and internal digital clocks for the
LMX9820A are derived from the reference clock at the
CLK+ input. This reference may either come from an exter-
nal clock or a dedicated crystal oscillator. The crystal oscil-
lator connections require a crystal and two grounded
capacitors.
It is important to consider board- and design-dependent
capacitance in tuning the crystal circuit. The following
equations allow a close approximation of the required crys-
tal tuning capacitance, but the actual values will vary with
the capacitive properties of the board. As a result, there is
some fine tuning of the crystal circuit which cannot be cal-
culated, but must be determined experimentally by testing
different values of load capacitance.
Many different crystals can be used with the LMX9820A. A
key requirement from the Bluetooth specification is 20
ppm. Additionally, ESR (Equivalent Series Resistance)
must be carefully considered. LMX9820A can support a
maximum of 230
100 ESR for best performance over voltage and tempera-
ture. See Figure 14 on page 22 for ESR as part of the crys-
tal circuit for more information.
8.7.1 Crystal
The crystal appears inductive near its resonant frequency.
It forms a resonant circuit with its load capacitors. The res-
onant frequency may be trimmed with the crystal load
capacitance.
1. Load Capacitance
For resonance at the correct frequency, the crystal should
be loaded with its specified load capacitance, which is the
value of capacitance used in conjunction with the crystal
unit. Load capacitance is a parameter specified by the
ESR, but it is recommended to stay <
(Continued)
18
crystal, typically expressed in pF. The crystal circuit shown
in Figure 10 on page 19 is composed of:
— C1 (motional capacitance)
— R1 (motional resistance)
— L1 (motional inductance)
— C0 (static or shunt capacitance)
The LMX9820A provides some of the load with internal
capacitors C
nal capacitors and tuning capacitors labeled Ct1 and Ct2
as shown in Figure 9. Ct1 and Ct2 should have the same
the value for best noise performance.
The LMX9820A has an additional internal capacitance
C
as:
C
The C
capacitance C
total capacitance is:
C
Based on the crystal specification and equation:
C
C
16.6 pF is very close to the TEW crystal requirement of 16
pF load capacitance. With the internal shunt capacitance
C
C
TUNE
L
total
L
L
total
total
= C
= C
= 8pF + 2.6pF + 6pF = 16.6pF
:
= C
= 16.6pF + 5pF = 21.6pF
CLK+
Figure 9. LMX9820A Crystal Recommended
L
int
int
of 2.6 pF. Crystal load capacitance (C
above does not include the crystal internal self-
L
+ C
+ C
+ C
Ct1
int
TUNE
TUNE
0
0
. The remainder must come from the exter-
as shown in Figure 10 on page 19, so the
+ Ct1/Ct2
+ Ct1//Ct2
LMX9820A
C
Crystal
C
TUNE
Circuit
int
CLK-
L)
is calculated
Ct2