Rainbow Electronics MAX2038 - Manual (Page 16)

MAX2038
Ultrasound VGA Integrated
with CW Octal Mixer
16 ______________________________________________________________________________________
CW Mixer Output Summation
The outputs from the octal mixer array are summed
internally to produce the total CWD summed beam-
formed signal. The octal array produces eight differen-
tial quadrature (Q) outputs and eight differential
in-phase (I) outputs. All quadrature and in-phase out-
puts are summed into single I and Q differential current
outputs (CW_QOUT+, CW_QOUT-, CW_IOUT+,
CW_IOUT-).
LO Phase Select
The LO phase dividers can be programmed through the
shift registers to allow for 4, 8, or 16 quadrature phases
for a complete CW beamforming solution.
CWD Beamforming Modes
There are four separate modes of operating the CWD
beamformer. See Table 1 for a summary of the different
modes of operation. The mode of operation can be
selected by the CW_M1 and CW_M2 logic inputs.
Phase generation is controlled through the serial inter-
face. See the
Serial Interface section in the Applications
Information section for details on how to program for dif-
ferent quadrature phases.
Mode 1
For mode 1 operation, the LO_LVDS input frequency is
typically 16 x f
LO . As the CWD LO frequency range is
1MHz to 7.5MHz, the input frequency ranges from
16MHz to 120MHz. This high LO clock frequency
requires a differential LVDS input. The 16 x f
LO input is
then divided by 16 to produce 16 phases. These 16
phases are generated for each of the 8 channels and
programmed for the selected phase by a serial shift
register. Each channel has a corresponding 5-bit shift
register, which is used to program the output phase of
the divide-by-16 circuit. The first 4 bits of the shift regis-
ter are for programming the 16 phases, the fifth bit
turns each channel on/off individually. For mode 1, set
both CW_M1 and CW_M2 to a logic-low.
CW_M1 CW_M2 MODE
LO INPUT
FREQUENCY
CLOCK
INTERFACE
PHASE
RESOLUTION
NO. OF
CLOCK
INPUTS
PER CHIP
PROGRAM
BY SERIAL
SHIFT
REGISTER
(SSR)
NO. OF
USEFUL
BITS IN
SSR
NO. OF
DON’T-
CARE BITS
IN SSR
0 0 1 16 x LVDS 16 phases 1 Yes 4 0
0 1 2 8 x LVDS 8 phases 1 Yes 3 1 MSB
1 0 3 4 x 3V CMOS 4 phases 8 Yes 2 2 MSBs
1 1 4 4 x 3V CMOS
Quadrature
provided
8 No N/A N/A
Table 1. Summary of CWD Beamforming Methods
MODE 1
CW_M1 = 0
CW_M2 = 0 MSB LSB SHUTDOWN
D C B A SD PHASE
(DEG) (B0) (B1) (B2) (B3) (B4)
0 0 0 0 0 0/1
22.5 0 0 0 1 0/1
45 0 0 1 0 0/1
67.5 0 0 1 1 0/1
90 0 1 0 0 0/1
112.5 0 1 0 1 0/1
135 0 1 1 0 0/1
157.5 0 1 1 1 0/1
180 1 0 0 0 0/1
202.5 1 0 0 1 0/1
225 1 0 1 0 0/1
247.5 1 0 1 1 0/1
270 1 1 0 0 0/1
292.5 1 1 0 1 0/1
315 1 1 1 0 0/1
337.5 1 1 1 1 0/1
Table 2. Mode 1 Logic Table (B4 = 0:
Channel On/B4 = 1: Channel Off)
N/A = Not applicable.