AK2401 Datasheet, PDF (5/103 Pages) Asahi Kasei Microsystems – Direct Conversion Transceiver

5.1. Block Diagram
5. Block Diagram and Functions
matching circuit and/or optional BPF
[AK2401]
from antenna and/or top filter
LNAIN
LNA
LNACONT
to power amplifier
BALUN
RFOUT_P
RFOUT_N
BIAS1
DRIVER AMP
VREF
BIAS2
VREF2
VREF1
TEST2
LDO
MIXER
PGA
AAF
+90
0
AGC
(LNA & PGA)
LOCAL
DIVIDER
1/(1,2,4,8)
FRACTIONAL-N
PLL SYNTHESIZER
ΔΣ
MODULATOR
R COUNTER
N DIVIDER
PHASE
FREQUENCY
DETECTOR
LOCAL
BUFFER
CHARGE
PUMP
I⁺
24-bit
ΔΣ ADC
I^-
Q⁺
24-bit
ΔΣ ADC
Q^-
1/4
CLOCK
BUFFER
DIGITAL FILTER
DC OFFSET
CAL
DC OFFSET
CAL
ADC
P/S IF
DAC
S/P IF
RSSI
12-bit
DAC
AD_SDO
AD_SCLK
AD_FS
MCU/
DSP
DA_SDI
DA_SCLK
DA_FS
SMF
DIGITAL CONTROL
to VCO modulation
SMFOUT
TEST1
LPF
VCO
LOOP
FILTER
Figure 1. AK2401 Block Diagram
MCU/DSP
5.2. Functions
The AK2401 consists of the Analog Receiving Circuit 1 (LNA), the Analog Receiving Circuit 2 (MIXER,
PGA and AAF), the Digital Receiving Circuit (ADC, DIGITAL FILTER, RSSI, AGC and ADC P/S IF), the
Local Oscillation Circuit (PLL SYNTHESIZER, LOCAL BUFFER, LOCAL DIVIDER and CLOCK
BUFFER), the Transmitting Data Generation Circuit (DAC S/P IF, DAC and SMOOTHING FILTER), the
Transmitting Pre-amplifier Circuit (DRIVER AMP), the Reference Voltage Generation Circuit (VREF), the
Internal Low Voltage Generation Circuit (LDO) and the Digital Control Circuit (DGITAL CONTROL).
 Analog Receiving Circuit 1 (LNA: Low Noise Linear Amplifier)
Amplify received RF signal in low noise. An automatic gain controlling (AGC) function that
automatically switches operation mode according to the input signal level is implemented to prevent
degradation of distortion characteristics in strong input environment. An external matching circuit is
needed at input/output of the LNA. An external filter can be added between the LNA and the MIXER
blocks depending on the Image suppression characteristic demands.
 Analog Receiving Circuit 2 (MIXER, PGA, AAF)
The direct conversion type MIXER down coverts RF signal that is amplified by LNA. The MIXER is
operated by two local signals with 90 degrees phase difference, and it generates Ich/Qch baseband
signal. A matching circuit is necessary at the MIXER input. The PGA (programmable gain amplifier)
is composed by a first-order low-pass filter that is able to change the gain by register settings. It
amplifies the dynamic range by keeping the input level of the ADC after this block. The PGA has an
AGC function that changes PGA gain automatically according to input signal level. The AAF is
composed by a third-order low-pass filter (Fc=100kHz). It is an anti-aliasing filter that prevents
aliasing at the ADC after this block. An analog filter is composed by the PGA and the AAF reducing
blocking signals on ADC input.
017003093-E-00
5
2017/3