AD9211 datasheet(23/29 Pages) AD

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AD9211

Rev. 0 | Page 22 of 28

600

–600

–400

–200

200

400

–3

–2

–1

0123

TIME (ns)

–100

100

TIME (ps)

Figure 49. Data Eye for LVDS Outputs in ANSI Mode with Trace Lengths

Greater than 24 Inches on Standard FR-4, AD9211-250

The format of the output data is offset binary by default. An

example of the output coding format can be found in Table 12.

If it is desired to change the output data format to twos comple-

ment, see the AD9211 Configuration Using the SPI section.

An output clock signal is provided to assist in capturing data

from the AD9211. The DCO is used to clock the output data

and is equal to the sampling clock (CLK) rate. In single data rate

mode (SDR), data is clocked out of the AD9211 and must be

captured on the rising edge of the DCO. In double data rate

mode (DDR), data is clocked out of the AD9211 and must be

captured on the rising and falling edges of the DCO. See the

timing diagrams shown in Figure 2 and Figure 3 for more

information.

Output Data Rate and Pinout Configuration

The output data of the AD9211 can be configured to drive 10

pairs of LVDS outputs at the same rate as the input clock signal

(single data rate, or SDR, mode), or five pairs of LVDS outputs

at 2× the rate of the input clock signal (double data rate, or DDR,

mode). SDR is the default mode; the device may be reconfigured

for DDR by setting Bit 3 in Register 14 (see Table 13).

Out-of-Range (OR)

An out-of-range condition exists when the analog input voltage

is beyond the input range of the ADC. OR is a digital output

that is updated along with the data output corresponding to the

particular sampled input voltage. Thus, OR has the same

pipeline latency as the digital data. OR is low when the analog

input voltage is within the analog input range and high when

the analog input voltage exceeds the input range, as shown in

Figure 50. OR remains high until the analog input returns to

within the input range and another conversion is completed. By

logically ANDing OR with the MSB and its complement, over-

range high or underrange low conditions can be detected.

OR DATA OUTPUTS

+FS – 1 LSB

+FS – 1/2 LSB

+FS

–FS

–FS + 1/2 LSB

–FS – 1/2 LSB

1111

0000

1111

0000

1111

1110

0001

0000

Figure 50. OR Relation to Input Voltage and Output Data

TIMING

The AD9211 provides latched data outputs with a pipeline delay

of seven clock cycles. Data outputs are available one propagation

delay (tPD) after the rising edge of the clock signal.

The length of the output data lines and loads placed on them

should be minimized to reduce transients within the AD9211.

These transients can degrade the converter’s dynamic performance.

The AD9211 also provides data clock output (DCO) intended for

capturing the data in an external register. The data outputs are valid

on the rising edge of DCO.

The lowest typical conversion rate of the AD9211 is 40 MSPS. At

clock rates below 1 MSPS, the AD9211 assumes the standby mode.

RBIAS

The AD9211 requires the user to place a 10 kΩ resistor between

the RBIAS pin and ground. This resister should have a 1%

tolerance and is used to set the master current reference of the

ADC core.

AD9211 CONFIGURATION USING THE SPI

The AD9211 SPI allows the user to configure the converter for

specific functions or operations through a structured register

space inside the ADC. This gives the user added flexibility to

customize device operation depending on the application.

Addresses are accessed (programmed or readback) serially in

one-byte words. Each byte may be further divided down into

fields, which are documented in the Memory Map section.

There are three pins that define the serial port interface or SPI

to this particular ADC. They are the SPI SCLK/DFS, SPI

SDIO/DCS, and CSB pins. The SCLK/DFS (serial clock) is used

to synchronize the read and write data presented the ADC. The

SDIO/DCS (serial data input/output) is a dual-purpose pin that

allows data to be sent and read from the internal ADC memory

map registers. The CSB is an active low control that enables or

disables the read and write cycles (see Table 9).

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