MD3872 datasheet(15/24 Pages) SUTEX

15 / 24 page

Supertex inc.

www.supertex.com

MD3872

Doc.# DSFP-MD3872

B060413

CW Cross-point Switch and Control

MD3872 consists of an 8x8 CW cross-point switch ma-

trix. There are eight differential inputs and eight differ-

ential outputs in the matrix. The differential inputs come

from the outputs of a differential transconductance ampli-

fier which is driven by the LNA directly. There are 16 out-

put pins for the eight differential outputs. The outputs of the

transconductance amplifier are current outputs, which can

be easily routed via switches and perform summing op-

erations for the CWD beamforming function. In single-end

mode, only non-inverting transconductance amplifier output

current is switched to the selected CW single-ended output.

Inverting transconductance amplifier output current is dis-

abled in this mode. All the cross-point switches in the CW

switch matrix can be programmed individually through the

SPI control interface. The whole CW mode operation occu-

pies four registers in the SPI interface registers map.

Power-Down Mode

The ADDR = 7, D6 is the PDC bit to control where the LNA,

CW-SW, VGA, AFF programmable reference current origi-

nates. If PDC = 0, the current usage of all four front-end

circuits will be referenced from the internal front-end circuit

current reference. Note that this circuit will not affect the cur-

rent usage of PLL, ADC and LVDS circuit. If PDC = 1, the

front-end circuits will refer to the external resistor current.

In normal operation, it is strongly recommended that the

internal reference be used, as it is optimized for the balance

of front-end circuits’ performance and power consumption. If

a 10% reduction in current is desired, set PDC = 1 and con-

nect an external bias resistor from EBC to GND. This will

sacrifice a certain amount of performance.Thus, if PDC = 1

and no external resistor is connected to the EBC pin (N.C.),

the total current consumption will be decreased to almost no

referenced current state.

Frequency (MHz)

0.1

1.0

-20

-40

-60

-80

-100

-120

-140

Frequency (MHz)

5.0

-20

-40

-60

-80

-100

-120

-140

Frequency (MHz)

5.0

-20

-40

-60

-80

-100

-120

-140

Frequency (MHz)

5.0

-20

-40

-60

-80

-100

-120

-140

Note:

Green: sine wave input to MD3872 on the evaluation board

Blue: some sine wave input to competitor on the evaluation board

Both at f

S = 40MHz, LNA RFB = 250Ω, Gain = 18dB, AAF = 1/3fS

Sample data length 32768 points FFT with Blackman-Harris Windowing

Fig. 1. MD3872 vs Competitor @1.4MHz

Fig. 2. MD3872 vs Competitor @1.4MHz

Fig. 3. MD3872 vs Competitor @5.0MHz

Fig. 4. MD3872 vs Competitor @7.0MHz

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