AD9961-EBZ datasheet(53/60 Pages) AD

53 / 60 page

AD9961/AD9963

Rev. 0 | Page 53 of 60

Digital Output Coding

The digital output coding is straight binary. The ideal transfer

characteristic for the auxiliary ADC is shown in Figure 86.

000 ... 000

000 ... 001

000 ... 010

111 ... 101

111 ... 110

111 ... 111

ANALOG INPUT

+0.5 LSB

1 LSB

+VFS – 1.5 LSB

+VFS – 1 LSB

Figure 86. Auxiliary ADC Transfer Function

Auxiliary ADC Conversion Cycle

A conversion is initiated by writing to SPI Register 0x77. The

conversion starts on the first rising edge of the AUXADCCLK

following a write to Register 0x77 (serial port register writes are

completed on the eighth rising edge of SCLK during the data

word write cycle). The conversion takes from 20 to 34

AUXADCCLK cycles to complete depending on the conversion

time setting programmed in Register 0x77. In most cases, the

ADC throughput is a function of both the serial port clock rate

and the ADC conversion time.

Figure 87 shows a typical timing scenario for an auxiliary ADC

conversion period. The scenario shows the write that initiates

the conversion, followed by the read that retrieves the conversion

result. In some cases, it may be required to add a wait time

between the write and read to ensure that the conversion is

complete. The wait time depends on the ADC conversion cycle

time and the speed of the serial port clock. The minimum wait

time is calculated as:

SCLK

AUXADCCLK

wait

−

≥

)

(

where N is the number of auxiliary ADC clock cycles that result

from the conversion time setting in Register 0x7B. tSCLK is the

serial port clock period. A negative wait time indicates no wait

time is required.

WRITE

INSTR.

WRITE

INSTR.

READ

INSTR.

DATA

REG

0x77

ADC

CONVERSION

ADC

CONVERSION

SERIAL

PORT

WAIT

DATA

REG

0x78

DATA

REG

0x77

DATA

REG

0x79

AUX ADC CYCLE 1

AUX ADC CYCLE 2

Figure 87. Timing Scenario for Auxiliary ADC Conversion Cycle

It should be noted that after initial power-up or recovery from

power-down, the ADC needs about 100 µS to stabilize. In many

cases, the results of the first conversion should be discarded in

order for the auxiliary ADC to reach an optimum operating

condition.

AUXILIARY DACs

The AD9963 has two 10-bit auxiliary DACs and two 12-bit

auxiliary DACs suitable for calibration and control functions.

The DACs have voltage outputs with selectable full-scale

voltages and output ranges. The auxiliary DACs are configured

and updated through the serial port interface.

10-Bit Auxiliary DACs

The two 10-bit DACs have identical transfer functions and are

output on the AUXIO2 and AUXIO3 pins. The two DACs can

be independently enabled and configured. The DACs have five

selectable top-of-scale voltages and four selectable output

ranges, which result in 20 possible transfer functions.

–

DACCODE[9:0]

AVDD

DAC10_RNG

0.5V

16k

Ω

AUXIO

DAC10_RNG: 00 = 2.0V = 124µA Ifs

01 = 1.5V = 93µA Ifs

10 = 1.0V = 62µA Ifs

11 = 0.5V = 31µA Ifs

RTOP

DAC10_TOP: 000 = 1.0V = 16k

Ω

001 = 1.5V = 8.0k

Ω

010 = 2.0V = 5.3k

Ω

011 = 2.5V = 4.0k

Ω

100 = 3.0V = 3.2k

Ω

ISPAN

Figure 88. Simplified Circuit Diagram of the 10-Bit Auxiliary DAC

The circuit is most easily analyzed using superposition of two

inputs to the op amp, the 0.5 V reference voltage, and the

programmable current source. The following equation describes

the no-load output voltage:

























−

Ω

SPAN

TOP

OUT

DACCODE

1024

The DACCODE (see Register 0x49 and Register 0x4A for

DAC10A and Register 0x46 and Register 0x47 for DAC10B) is

interpreted such that ISPAN is full scale at 0x000 and zero at 0x3FF.

This leads to an increasing output voltage with increasing code

as shown in Figure 89 and Figure 90. The five selectable gain

setting resistors of 3.2 kΩ, 4.0 kΩ, 5.3 kΩ, 8.0 kΩ, and 16 kΩ

result in full-scale output voltage levels of 3.0 V, 2.5 V, 2.0 V,

1.5 V and 1.0 V respectively. The four selectable full-scale

currents of 31 µA, 62 µA, 93 µA and 124 µA result in voltage

output spans of 0.5 V, 1.0 V, 1.5 V, and 2.0 V, respectively.

AD9961-EBZ 데이터시트(PDF) 53 Page - Analog Devices

AD9961-EBZ 데이터시트(HTML) 53 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

데이터시트 다운로드

링크 URL