AK2401 Datasheet, PDF (6/103 Pages) Asahi Kasei Microsystems – Direct Conversion Transceiver

[AK2401]
 Digital Receiving Circuit (ADC, DIGITAL FILTER, RSSI, AGC, ADC P/S IF)
The 24-bit delta-sigma A/D converter converts an analog baseband signal that is generated at the
analog receiving circuit to a digital baseband signal. The digital filter is composed by a decimation
filter and a channel filter for removing adjacent channel interference and blocking. The channel filter
is selected from 10 types standard channel filters that have different frequency characteristics and
FIR filter that can be set the coefficient arbitrary. The narrowest pass band of the standard channel
filters is 2 kHz and the widest is 60 kHz. The output sampling frequency differs depending on the type
of selected channel filter, and it will be 150 kHz at maximum when using a 19.2 MHz reference clock.
A DC OFFSET CAL block is composed of a real-time DC offset canceller (RDOC) and a DC offset
calibrator. It cancels DC offset that is superimposed to a baseband signal. The RSSI outputs a
signal-strength level of the DC OFFSET CAL output. It can be confirmed by register read on SPI. The
parallel interface for ADC outputs digital baseband signals.
 Local Generation Circuit (PLL SYNTHESIZER, LOCAL BUFFER, LOCAL DIVIDER, CLOCK
BUFFER)
The FRACTIONAL-N PLL is composed by a PLL SYNTHESIZER, external LOOP FILTER and VCO.
It generates a local frequency signal by multiplying the reference clock from the TCXOIN pin by “N”,
and converts to a local frequency by dividing the signal by “N” (N=1, 2, 4, 8) at LOVAL DIVIDER. At
the same time, two local signals that have 90 degree phase difference are generated.
 Transmitting Data Generation Circuit (DAC S/P IF, DAC, SMF)
The 12-bit DA converter converts a digital baseband signal that is input to a serial/parallel interface
for DAC to an analog baseband signal. The SMF (SMOOTHING FILTER) is a low-pass filter
(fc=20kHz) that smoothing the DAC output. These circuits are used for generating an audio signal of
transmission and connected to voltage control pin of an external VCO. In other case, it is able to be
used as a general purpose 12-bit DAC.
 Transmitting Pre-amplifier Circuit (DRIVER AMP)
This circuit amplifies a signal that is divided by “N” by the LOCAL DIVIDER and outputs. It is
assumed to use as a transmitting signal output when modulating the signal directly by an external
VCO.
 Reference Voltage Generation Circuit (VREF)
Generate reference voltage for each block.
 Internal Low Voltage Generation Circuit (LDO)
Generate a 1.9V power from external 3V power (SYNVDD). This internal power supply is supplied to
the digital receiving circuit, the digital control circuit and a part of local oscillation circuit.
 Digital Control Circuit (DIGITAL CONTROL)
• Register Write/Read by 4-wire Serial Interface
(CSN, SCLK, SDATAI, SDATAO pins)
• Hardware Reset Signal Input (RSTN pin)
• AGC Function Control Signal Input (AGC_KEEP pin)
• PLL Status Output (LD pin)
• Power Management by Pins (RX_PDN, TX_PDN pins)
017003093-E-00
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2017/3