Renesas RL78 Series User Manual page 634

16-bit single-chip microcontrollers

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15.3.6 Analog block

The analog block consists of the circuits for RF transmission and reception. Figure15-4 shows a block diagram of the

RF transmission/reception circuit block.

When the analog block is operating as a transmitter, the output from the power amplifier (PA) in the transmitter

section is sent to the antenna. When it is operating as a receiver, it receives signals input to the antenna and feeds

them to the LNA in the reception section.

This block also has a facility for cutting off the signal so that signals do not leak to the reception block during

transmission or to the transmission block during reception.

This circuit is located at the first stage of an analog circuit which receives high-frequency signals fetched at the

antenna as the input. When a received signal is very small, this circuit amplifies the signal to prevent noise

generated at the subsequent circuitry from degrading the carrier-to-noise ratio (CNR). On the contrary, if the input

signal is large, according to the case, the signal level may be adjusted (e.g., attenuated) in order to minimize the

signal distortion in the LNA or subsequent circuitry.

This is a mixer circuit that changes the frequency of high-frequency RF signals output from LNA into base band

(BB) signals with low frequency.

This consists of a filter core unit, tuning unit, capacitor between the mixer filters, capacitor between the filters and

VGA, and bias circuit.

(5) Variable gain amplifier (VGA)

This changes the amplitude so that the most suitable amplitude can be provided to the A/D converter which is

connected at a subsequent stage of the analog circuit.

A successive approximation ADC is used.

R01UH0515EJ0120 Rev.1.20

Dec 16, 2016

Figure15-4. RF Transmission/Reception Circuit Block

CHAPTER 15 RF TRANSCEIVER

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