MAX19700 查看數據表（PDF） - Maxim Integrated

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MAX19700

7.5Msps, Ultra-Low-Power Analog Front-End

Maxim Integrated 

7.5Msps, Ultra-Low-Power

Analog Front-End

SPI Register Description

The operating modes can be selected by programming

the control bits, A3–A0, in the register as shown in Table

3. Modifying A3–A0 bits will select from ENABLE-16,

Aux-DAC1, Aux-DAC2, Aux-DAC3, IOFFSET, QOFFSET,

and COMSEL modes. ENABLE-16 is the default operat-

ing mode. This mode allows for shutdown, idle, and

standby states as well as switching between FAST,

SLOW, Rx, and Tx modes. Table 4 shows the

MAX19700 power-management modes. Table 5 shows

the T/R pin-controlled external Tx-Rx switching modes.

Table 6 shows the SPI-controlled Tx-Rx switching

modes.

In ENABLE-16 mode, the aux-DACs have independent

control bits E6, E5, and E4, and the Tx-path full-scale

output can be set with bit E7. Table 7 shows the auxil-

iary DAC enable codes and Table 8 shows the full-

scale output selection. Bits E11 and E10 are reserved

and need to be programmed to logic-low. Bits E9 and

E8 are not used.

Modes Aux-DAC1, Aux-DAC2, and Aux-DAC3 select

the aux-DAC channels named DAC1, DAC2, and DAC3

and hold the data inputs for each DAC. Bits _D11–_D0

are the data inputs for each aux-DAC and can be pro-

grammed through SPI. The MAX19700 also includes

two 6-bit registers that can be programmed to correct

the offsets for the Tx-path I and Q channels indepen-

dently (see Table 9). Use the COMSEL mode to select

the output common-mode voltage with bits CM1 and

CM0 (see Table 10).

Shutdown mode offers the most dramatic power sav-

ings by shutting down all the analog sections of the

MAX19700 and placing the Rx ADC digital outputs in

tri-state mode. When the Rx ADC outputs transition

from tri-state to active, the last converted word is

placed on the digital outputs. The Tx DAC previously

stored data is lost when coming out of shutdown mode.

The wake-up time from shutdown mode is dominated

by the time required to charge the capacitors at REFP,

REFN, and COM. In internal reference mode and

buffered external reference mode, the wake-up time is

typically 75µs to enter Rx mode and 25µs to enter Tx

mode.

In idle mode, the reference and clock distribution cir-

cuits are powered, but all other functions are off. The

Rx ADC outputs are forced to tri-state. The wake-up

time is 7.3µs to enter Rx mode and 5µs to enter Tx

mode. When the Rx ADC outputs transition from tri-

state to active, the last converted word is placed on the

digital outputs.

In standby mode, the reference is powered, but the rest

of the device functions are off. The wake-up time from

standby mode is 7.3µs to enter Rx mode and 25µs to

enter Tx mode. When the Rx ADC outputs transition

from tri-state to active, the last converted word is

placed on the digital outputs.

FAST and SLOW Rx and Tx Modes

In addition to the external Tx-Rx control, the MAX19700

also features SLOW and FAST modes for switching

between Rx and Tx operation. In FAST Tx mode, the Rx

ADC core is powered on but the ADC core digital out-

puts are tri-stated on the D0–D9 bus; likewise, in FAST

Rx mode the transmit path (DAC core and Tx filter) is

powered on but the DAC core digital inputs are tri-stat-

ed on the D0–D9 bus. The switching time between Tx

to Rx or Rx to Tx is FAST because the converters are

on and do not have to recover from a power-down

state. In FAST mode, the switching time between Rx to

Tx and Tx to Rx is 1µs. However, power consumption is

higher in this mode because both the Tx and Rx cores

are always on. To prevent bus contention in these

states, the Rx ADC output buffers are tri-stated during

Tx and the Tx DAC input bus is tri-stated during Rx.

In SLOW mode, the Rx ADC core is off during Tx; like-

wise the Tx DAC and filters are turned off during Rx to

yield lower power consumption in these modes. For

example, the power in SLOW Tx mode is 31.2mW. The

power consumption during Rx is 21mW compared to

power consumption in FAST mode of 38.4mW. However,

the recovery time between states is increased. The

switching time in SLOW mode between Rx to Tx is 5µs

and Tx to Rx is 7.3µs.

External T/R Switching Control vs.

Serial-Interface Control

Bit E3 in the ENABLE-16 register determines whether

the device Tx-Rx mode is controlled externally through

the T/R input (E3 = low) or through the SPI command

(E3 = high). By default, the MAX19700 is in the external

Tx-Rx control mode. In the external control mode, use

the T/R input (pin 27) to switch between Rx and Tx

modes. Using the T/R pin provides faster switching

between Rx and Tx modes. To override the external Tx-

Rx control, program the MAX19700 through the serial

interface. During SHDN, IDLE, or STBY modes, the T/R

input is overridden. To restore external Tx-Rx control,

program bit E3 low and exit the SHDN, IDLE, or STBY

modes through the serial interface.

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