MC72000 Freescale Semiconductor, MC72000 Datasheet - Page 33

• Manufacturer Part Number: MC72000
• Description: Integrated Bluetooth Radio
• Manufacturer: Freescale Semiconductor

The LNA can be matched to 50 Ω by a simple capacitor/inductor network as shown in Figure 6.
When the LNA is disabled or the device is in the Idle or Transmit mode, the impedance of the LNA
becomes the value shown in Table 16.
The use of an antenna switch to interface the LNA with an antenna is the preferred circuit configuration as
shown in Figure 92.
In this implementation, a true RF Single-Pole, Double-Throw (SPDT) switch is used to isolate the PA
output from the LNA input during receive and transmit modes. A 1/4 wavelength trace is not required. As
a result, this implementation has the highest performance (due to the lowest loss) and smallest size at the
penalty of increased system cost. An external switch must be used for Class 1 Bluetooth devices as the
LNA input will become overloaded if not sufficiently isolated from the external PA output. The LNA
provides a nominal 6.7 dB of power gain when properly matched. The LNA is enabled approximately
150 µs after the assertion of the RTXEN pin when programmed for Receive mode. It is disabled
immediately after the deassertion of the RTXEN pin or during any Idle or Transmit mode.
6.3.2 High/Low Image Reject Mixer (I/R Mixer)
The mixer is used to convert the desired RF channel to a 6.0 MHz Intermediate Frequency (IF). The mixer
is completely balanced on all ports, and the local oscillator (LO) is derived from the buffered output of the
on-chip voltage controlled oscillator (VCO).
In general, it is desirable to keep all image frequencies in-band. Therefore, when receiving the six lowest
channels, the mixer can be programmed for high-side injection and the LO will be programmed to be
6.0 MHz above the desired channel frequency. When receiving the six highest channels, the mixer can be
programmed for low-side injection, and the LO will be programmed to be 6.0 MHz below the desired
channel frequency. This is shown in Figure 7. Selection of high or low side injection is accomplished by
bit R2/11 of the register map. For all other in-band channels, the choice of high or low side injection is
arbitrary. The baseband uses high-side injection for frequencies up to 2.441-GHz inclusive and low-side
injection thereafter.
MOTOROLA
Freescale Semiconductor, Inc.
Figure 6. Simple Capacitor/Inductor Network
Frequency
Frequency
For More Information On This Product,
MC72000 Advance Information Data Sheet
2.45 GHz
2.45 GHz
Table 16. S11 for LNA During Receive
Table 17. S11 for LNA Disabled
Go to: www.freescale.com
C
Block
C
match
Preliminary
MAG
MAG
(dB)
TBD
(dB)
TBD
L
match
LNA
(degree)
(degree)
Angle
Angle
TBD
TBD
Radio Functional Description
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