AD5932YRUZ-REEL7(Rev0) Просмотр технического описания (PDF) - Analog Devices

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AD5932YRUZ-REEL7
(Rev.:Rev0)

Programmable Frequency Scan Waveform Generator

Analog Devices 

AD5932

Therefore, in this example, a time interval of 20 ns × 2047 = 40 μs

is the maximum, with the minimum being 40 ns. For some

applications, this maximum time of 40 μs may be insufficient.

Therefore, to allow for sweeps that need a longer increment

interval, time-base multipliers are provided. D12 and D11 are

dedicated to the time-base multipliers, as shown in the bit map

above. A more detailed table of the multiplier options is given in

Table 9.

Table 9. Time-Base Multiplier Values

D12

D11

Multiplier Value

0

0

Multiply (1/MCLK) by 1

0

1

Multiply (1/MCLK) by 5

1

0

Multiply (1/MCLK) by 100

1

1

Multiply (1/MCLK) by 500

If MCLK = 50 MHz and a multiplier of 500 is used, then the

base interval (TBASE) is now (1/(50 MHz) x 500)) = 10 μs. Using

a multiplier of 500, the maximum increment interval is 10 μs ×

211 − 1 = 20.5 ms. Therefore, the option of time-base multipliers

gives the user enhanced flexibility when programming the

length of the frequency window, because any frequency can be

output for a minimum of 40 ns up to a maximum of 20.5 ms.

The above example shows a fixed number of clock periods.

Note that the same equally applies to fixed numbers of clock

cycles.

Length of Scan Time

The length of time to complete a user-programmed frequency

scan is given by the following equation:

TSCAN = (1 + NINCR) × TBASE

ACTIVATING AND CONTROLLING THE SCAN

After the registers have been programmed, a 0 to 1 transition

on the CTRL pin starts the scan. The scan always starts from

the frequency programmed into the FSTART register. It changes by

the value in the Δf register and increases by the number of steps

in the NINCR register. However, the time interval of each frequency

can be internally controlled using the tINT register or externally

controlled using the CTRL pin. The available options are

• Auto-increment

• External increment

Auto-Increment Control

The value in the tINT register is used to control the scan. The

AD5932 outputs each frequency for the length of time pro-

grammed in the TINT register, before moving on to the next

frequency.

To set up the AD5932 to this mode, INT/EXT INCR (Bit D5)

must be set to 0.

External Increment Control

In this case, the time interval, tINT, is set by the pulse rate on the

CTRL pin. The first 0 to 1 transition on the pin starts the scan.

Each subsequent 0 to 1 transition on the CTRL pin increments

the output frequency by the value programmed into the Δf register.

To set up the AD5932 to this mode, INT/EXT INCR (Bit D5)

must be set to 1.

INTERRUPT Pin

This function is used as an interrupt during a frequency scan.

A low-to-high transition on this pin is sampled by the internal

MCLK, thereby resetting internal state machines, which results

in the output going to midscale.

STANDBY Pin

Sections of the AD5932 that are not in use can be powered

down to minimize power consumption. This is done by using

the STANDBY pin. For optimum power savings, it is recom-

mended to reset the AD5932 before entering standby. Doing so

reduces the power-down current to 20 μA.

When this pin is high, the internal MCLK is disabled, and the

reference, DAC, and regulator are powered down. When in this

state, the DAC output of the AD5932 remains at its present

value, because the NCO is no longer accumulating. When the

device is taken back out of standby mode, the MCLK is re-

activated, and the scan continues. To ensure correct operation

for new data, it is recommended that the device be internally

reset, using a control register write or using the INTERRUPT

pin, and then restarted.

Rev. 0 | Page 18 of 28

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