MC13180 Datasheet, PDF (40/58 Pages) Motorola, Inc – 2.4 GHz Low Power Wireless Transceiver IC for Bluetooth™ Applications

Functional Description
4.27 Receiver
The MC13180 receiver is intended to be used in Time Division Duplex (TDD), Frequency Hopping
Spread Spectrum (FHSS) applications such as Bluetooth. The receiver uses a low intermediate frequency
(IF) of 6.0 MHz, and is capable of receiving up to 1.0 Mbit/s Gaussian Frequency Shift Keyed (GFSK)
serial data through the entire 2.4 GHz Industrial, Scientific and Medical (ISM) band.
The output of the receiver is a demodulated, serial bit stream of 24 Mbit/s data. This data represents a 4X
over sample by a 6-bit D/A of the actual demodulated analog data recovered from the desired channel. A
detailed discussion of each of the functional blocks within the receiver follows.
4.28 LNA
The first portion of the receiver chain is the Low Noise Amplifier (LNA). The LNA is a bipolar cascode
design and provides gain with low noise at RF frequencies. The LNA is designed with a single-ended
(unbalanced) input and is converted to a differential (balanced) output by means of an on chip, integrated
balun.
For optimum performance, the LNA input impedance must be matched to the complex conjugate of the
source impedance (usually 50 Ω).
The LNA of the MC13180 exhibits two distinctly different impedances depending upon whether the LNA
is active or disabled. During a receive cycle, the S11 of the LNA is shown in Table 20.
Table 20. S11 for LNA During Receive
Frequency
MAG
(dB)
Angle
(degree)
2.45 GHz
-4.3
-138
The LNA can be matched to 50 Ω by a simple capacitor/inductor network as shown in Figure 24.
C_Block
C_match
L_match
LNA
Figure 24.
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 21.
Table 21. S11 for LNA Disabled
Frequency
MAG
(dB)
Angle
(degree)
2.45 GHz
-8.9
42
The use of an antenna switch to interface the LNA with an antenna is the preferred circuit configuration as
illustrated in Figure 42.
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
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