AD9739-R2-EBZ datasheet(31/48 Pages) AD

31 / 48 page

Data Sheet

AD9739

Rev. B | Page 31 of 48

LVDS INPUTS

(NO FAIL-SAFE)

LVDS

RECEIVER

GND

100Ω

VP,N

VCOM

= (VP + VN)/2

LOGIC BIT

EQUIVALENT

EXAMPLE

1.4V

1.0V

0.4V

–0.4V

LOGIC 1

LOGIC 0

Rotating the CLKDIVPH phase provides a means of adjusting

the delay in course steps of fDAC/4. For example, in the 800 MSPS

and 1600 MSPS cases described above, rotating the CLKDIVPH

setting by 1 corresponds to a delay shift of 5 ns and 2.5 ns,

respectively. By adding an additional step in the SPI initialization

routine for the data receiver controller, it becomes possible to

increase the effective range of the delay line to ensure a

DCI_DEL value that falls within a reasonable guard band.

LVDS Driver and Receiver Input

The AD9739 features a LVDS-compatible driver and receivers.

The LVDS driver output used for the DCO and SYNC_OUT

signal includes an equivalent 200 Ω source resistor that limits its

nominal output voltage swing to ±200 mV when driving a

100 Ω load. The DCO output driver can be powered down via

DCO_N

VSS

VDD33

DCO_P

V+

V–

100Ω

VCM

100Ω

ESD

Figure 46. LVDS Data Input Levels

100Ω

VDD33 = 3.3V

LVDS_1

LVDS_N

LVDS_2

VP = 1.4V

R1 = 4.75 × 100/N

R2 = 2.50 × 100/N

Figure 44. Equivalent LVDS Output

VSS

VDD33

DCI_P

DBx[13:0]P

DCI_N

DBx[13:0]N

100Ω

ESD

Figure 45. Equivalent LVDS Input

The LVDS receivers include 100 Ω termination resistors, as

shown in Figure 45. These receivers meet the IEEE-1596.3-1996

reduced swing specification (with the exception of input hysteresis,

which cannot be guaranteed over all process corners). Figure 46

and Figure 47 show an example of nominal LVDS voltage levels

seen at the input of the differential receiver with resulting common-

mode voltage and equivalent logic level. The LVDS receivers

can be powered down via Register 0x01, Bit 4.

Figure 47. Resistor Network to Bias Unused LVDS Data Inputs

The AD9739 LVDS inputs do not include fail-safe capability.

Any unused data input pins should be biased with an external

network or static driver. Figure 47 shows an external biasing

network that can be used to place unused data bits into a known

state. The resistor values for R1 and R2 are selected to establish

a VP and VN of 1.4 V and 1.0 V, respectively, depending on the

number of unused digital inputs, N.

Table 27. Example of LVDS Input Levels

Applied Voltages

Resulting Differential Voltage

Resulting Common-Model Voltage

VP (V)

VN (V)

VP, N

VCOM

Logic Bit Binary Equivalent

1.4

1.0

+0.4 V

1.2 V

1.0

1.4

−0.4 V

1.2 V

1.0

0.8

+200 mV

900 mV

0.8

1.0

−200 mV

900 mV

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