AD6620
after SDFS makes the first bit available at SDO. The falling
edge of serial clock can be used to sample the data. The total
number of bits are then read from the AD6620 (determined by
the serial port word length). If the DSP has the ability to count
bits, the DSP will know when the complete frame is read. If not,
the DSP can monitor the SDFE pin to determine that the com-
plete frame is read. The serial clock provided by the DSP can be
asynchronous with the AD6620 clock and input data.
2
4
WL AD SDIV
SCLK
SCLK
DT
SDI
SDO
DSP
AD6620
DR
SDFS
SDFE
RFS
10k⍀
10k⍀
SBM
2
4
WL AD SDIV
SCLK
+3.3V
SCLK
DT
Figure 30. Typical Serial Data Output Interface to DSP
(Serial Master Mode, SBM = 1)
SDI
SDO
DSP
AD6620
DR
Figure 31 shows two AD6620s illustrating the cascade capability
for the chip. The first is connected as a serial master and the
second is configured in serial cascade mode. The SDFE signal
of the master is connected to the SDFS of the slave. This allows
the master AD6620 data to be obtained first by the DSP, fol-
lowed by the cascaded AD6620 data.
SDFS
RFS
10k⍀
10k⍀
SDFE
OUT
DV
SBM
IRQ
Figure 32. Typical Serial Data Output Interface to DSP
(Serial Slave Mode, SBM = 0)
2
4
WL AD SDIV
SCLK
SCLK
DT
In either the serial master or slave mode, there are two con-
straints that must be observed. The first is that the clock must
be fast enough to read the serial frame prior to the next frame
becoming available. Since the AD6620 output is synchronous
with its input sample rate, the output update rate can be deter-
mined by the user-programmed decimation rate. The timing
diagram in Figure 33 details how serial slave mode is imple-
mented. The second constraint is that the time between serial
frames may be either zero SCLK periods (the end of one frame
adjoins the beginning of the next) or two or more SCLK peri-
ods. One SCLK period between frames is not allowed.
SDI
SDO
DSP
AD6620
DR
SDFS
SDFE
RFS
SBM
+3.3V
4
2
WL AD SDIV
SCLK
tDSO
SDI
SDO
SCLK
AD6620
DV
PULSEWIDTH IS 2 CLKIN
OUT
CASCADE
SINGLE CHANNEL AND 4 CLKIN
DUAL CHANNEL
SDFS
SDFE
DV
OUT
10k⍀
10k⍀
SBM
DSP USES FALLING EDGE OF
OUT
DV
TO GENERATE SDFS
SDFS
SDO
Figure 31. Typical Serial Data Output Interface to DSP
(Serial Cascade Mode, SBM = 0)
IMSB
IMSB – 1
FIRST DATA IS AVAILABLE THE FIRST
RISING SCLK AFTER SDFS GOES HIGH
The AD6620 also supports a serial slave mode, where the serial
clock and interface is provided by a DSP or ASIC that is set to
operate in the master mode. Note that the AD6620 cannot be
booted through the serial port. The microport must be used to
initialize the device, then serial operation is supported.
Figure 33. Timing for Serial Slave Mode (SBM = 0)
FREQUENCY TRANSLATOR
The first signal processing stage is a frequency translator con-
sisting of two multipliers and a 32-bit complex numerically
controlled oscillator (NCO). The NCO serves as a quadrature
local oscillator capable of producing any analytic frequency
between –fSAMP/2 and +fSAMP/2 with a resolution of fSAMP/232. In
the Single Channel Real input mode, fSAMP is equal to fCLK multi-
plied by the fraction of CLK cycles that A/B is high. In the
Diversity Channel Real and Single Channel Complex input
In the serial slave mode, DVOUT is valid and indicates the pres-
ence of a new word in the output buffers of the shift register.
This pin may thus be used by the DSP to generate an interrupt
to service the serial port. The DSP then generates an SFDS
pulse to drive the AD6620. The first serial clock rising edge
REV. A
–19–
ADI [ ADI ]
