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AD9873

Analog Front End Converter for Set-Top Box, Cable Modem

Analog Devices 

AD9873

REGISTER BIT DEFINITIONS

00h, Bits 0–4: OSC IN Multiplier–Register Address

This register field is used to program the on-chip multiplier (PLL)

that generates the chip’s high-frequency system clock, fSYSCLK.

For example, to multiply the external crystal clock fOSCIN by 19

decimal, program register address 00h, Bits 5–1 as 13h. Default

value is M = 16 = 10h. Valid entries range from M = 1 to 31.

M = 1 (no PLL) requires a very stable, high-frequency clock at

OSC IN. A changed fSYSCLK frequency is stable (PLL locked)

after a maximum of 200 fMCLK cycles (= Wake-Up Time).

00h, Bit 5: RESET

Writing a one to this bit resets the registers to their default val-

ues and restarts the chip. The RESET bit always reads back

0. Register address 00h bits are not cleared by this software reset.

However, a low level at the RESET pin would force all registers,

including all bits in address 00h, to their default state.

00h, Bit 6: LSB/MSB First

Active high indicates SPI serial port access of instruction byte

and data registers is least significant bit (LSB) first. Default low

indicates most significant bit (MSB) first format.

00h, Bit 7: SDIO Bidirectional

Default low indicates SPI serial port uses dedicated input/output

lines (SDIO and SDO pin). High configures serial port as single

line I/O (SDIO pin is used bidirectional).

01h, Bits 0–5: MCLK Divider

This register is used to divide the chip’s master clock by R, where

R is an integer between 2 and 63. The generated reference clock,

REF CLK, can be used for external frequency-controlled

devices. Default value is R = 9.

01h, Bit 6: OSC IN Divider

The OSC IN multiplier output clock can be divided by 4 or 3 to

generate the chip’s master clock. Active high indicates a divide

ratio of N = 3. Default low configures a divide ratio of N = 4.

01h, Bit 7: PLL Lock Detect

If this bit is set to 1, REF CLK pin is disabled from the nor-

mal usage. In this mode REF CLK high signals that the internal

phase lock loop (PLL) is in lock with CLK IN.

02h Bits 0–7: Power-Down

Sections of the chip that are not used can be put in a power saving

mode when the corresponding bits are set to 1. This register has

a default value of 00h with all sections active.

Bit 0: Power-Down 8-bit ADC powers down the 8-bit ADC

and stops RxSYNC framing signal.

Bit 1: Power-Down 10-bit ADC reference powers down the

internal 10-bit ADC reference.

Bit 2: Power-Down 10-bit ADC powers down the 10-bit ADC.

Bit 3: Power-Down 12-bit ADC reference powers down the

internal 12-bit ADC reference.

Bit 4: Power-Down 12-bit ADC powers down the 12-bit ADC.

Bit 5: Power-Down Tx powers down the transmit section of

the chip.

Bit 6: Power-Down DAC Tx powers down the DAC.

Bit 7: Power-Down PLL powers down the CLK IN Multiplier.

03h to 06h: Sigma-Delta Output Control Words

The Sigma-Delta Output Control Words –0 and –1 are 12 bits

wide and split in MSB bits <11:4> and LSB bits <3:0>. Changes

to the sigma-delta outputs take effect immediately for every MSB

or LSB register write. Sigma-delta output control words have a

default value of 0. The smaller the programmed values in these

registers, the lower are the integrated (low-pass filtered) sigma

delta output levels (straight binary format).

07h, Bits 0–6: Clamp Level Control for Video Input

A 7-bit clamp level offset can be set for the internal automatic

clamp level control loop of the Video Input.

Clamp level offset = Clamp level control × 16.

This register defaults to 32 = 20h, which amounts to a clamp

level offset of 512 LSB = 200h. Valid clamp level control values

are 16 to 127.

07h, Bit 7: Video Input Enable

This bit controls the multiplexer to the 12-bit ADC and deter-

mines if IF12 input or Video input is used. The bit is default set

to 0 for the IF12 input.

08h, Bit 0: Test 10-Bit ADC

Active high allows nonmultiplexed 10-bit ADC data only to be

read at IF outputs. Output data changes at half MCLK clock rate.

This bit defaults to 0.

08h, Bit 1: Test 12-Bit ADC

Active high allows nonmultiplexed 12-bit ADC data only to be

read at IF outputs. Output data changes at half MCLK clock rate.

This bit defaults to 0.

08h, Bit 5 and Bit 7: ADC Clock Select

Active high indicates that the frequency at OSC IN is directly used

to sample the on chip ADCs. Default low indicates that the on

chip ADCs generate their sampling frequencies from the internally

generated master clock MCLK. Both Bit 5 and Bit 7 need to be

programmed with the same values.

0Ch, Bits 0–3: Version

This register stores the die version of the chip. It can only be read.

0Fh, Bit 0: Single-Tone Tx Mode

Active high configures the AD9873 for single-tone applications.

The AD9873 will supply a single frequency output as determined

by the frequency tuning word (FTW) selected by the active

profile. In this mode, the Tx IQ input data pins are ignored

but should be tied high or low. Default value of single-tone

Tx mode is 0 (inactive).

0Fh, Bit 1: Spectral Inversion Tx

When set to 1, inverted modulation is performed

(I cos (ωt) + Q sin (ωt)).

Default is logic zero, noninverted modulation

(I cos (ωt) – Q sin (ωt)).

0Fh, Bit 2: Bypass Inv Sinc Tx Filter

Active high, configures the AD9873 to bypass the SIN(X)/X

compensation filter. Default value is 0 (inverse sinc filter enabled).

–12–

REV. 0

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