Vga clamp, Power-down, Overload recovery – Rainbow Electronics MAX2038 User Manual

Page 15: Octal continuous wave (cw) mixer

MAX2038

Ultrasound VGA Integrated

with CW Octal Mixer

______________________________________________________________________________________

VGA Clamp

A clamp is provided to limit the VGA output signals to
avoid overdriving the ADC or to prevent ADC satura-
tion. Set VG_CLAMP_MODE low to clamp the VGA dif-
ferential outputs at 2.4V

P-P

. Set the VG_CLAMP_MODE

high to disable the clamp.

Power-Down

The device can also be powered down with PD. Set PD
to logic-high for power-down mode. In power-down
mode, the device draws a total supply current of 27mA.
Set PD to a logic-low for normal operation.

Overload Recovery

The device is also optimized for quick overload recovery
for operation under the large input-signal conditions that
are typically found in ultrasound input buffer imaging
applications. See the

Typical Operating Characteristics

for an illustration of the rapid recovery time from a trans-
mit-related overload.

Octal Continuous Wave (CW) Mixer

The MAX2038 CW mixers are designed using an active
double-balanced topology. The mixers achieve high
dynamic range and high linearity performance, with
exceptionally low noise, which is ideal for ultrasound
CWD signal reception. The octal quadrature mixer
array provides noise performance of -155dBc/Hz at
1kHz from a 1.25MHz carrier, and a two-tone third-
order ultrasound specific intermodulation product of
typically -50dBc. See the

Ultrasound-Specific IMD3

Specification

in the

Applications Information

section

The octal array exhibits quadrature and in-phase differ-
ential current outputs (CW_QOUT+, CW_QOUT-,
CW_IOUT+, CW_IOUT-) to produce the total CWD
beamformed signal. The maximum differential current
output is typically 3mA

P-P

and the mixer output-compli-

ance voltage ranges from 4.75V to 12V.

CHANNEL 1

I/Q

DIVIDER

PHASE

SELECTOR

5-BIT

I Q

DIN

CLK

LO_LVDS+

LO_LVDS-

CWIN1

CWIN2

CWIN8

GND

CW_M2

CW_M1

CW_IOUT+

DOUT

LOW_PWR

CW_IOUT-

CW_QOUT-

CW_QOUT+

CW_IOUT2+

CW_QOUT2-

LOAD

LO1

LO2

LO8

REF

CW_FILTER

M4_EN

•

• • •
• • •

• • •

•

MAX2038

I Q

CHANNEL 2

I/Q

DIVIDER

PHASE

SELECTOR

CHANNEL 8

I/Q

DIVIDER

PHASE

SELECTOR

High-Level CW Mixer and Programmable

Beamformer Functional Diagram