Arizona Microtek, Inc.

AZT71

Programmable Capacitive Tuning IC

www.azmicrotek.com

+1-480-962-5881

6

Request a Sample

May 2012, Rev 1.2

To initially determine the capacitance value for the desired center frequency of the oscillator one should set the

capacitance of the AZT71 directly from the active shift register bits. To accomplish this, the CLK pin is left high after the

last control word bit has been shifted in. Figure 7 shows the control word 11001100100 has been serially entered into the

register. Note that bit0 is the 1

but still must be included in the serial bit stream. For the shift register, capacitors are selected when bits are active HIGH.

t

DA

CLK

bit 0

bit 1

bit 2

bit 3

bit 4

bit 5

bit 6

bit 7

bit 8

bit 9

bit 10

Register data

active when

CLK is high

bit 0

Figure 7 - Shift register programming

Once the desired capacitance value has been determined, the digital control word can be written or re-written into the

EEPROM. By storing the control word in the EEPROM, the customer is prevented from making adjustments from the

factory set programming data. This is accomplished within the AZT71 with internal pull-downs on the DA, PV, and CLK

pins. The detailed sequence for writing data to the EEPROM within the AZT71 is described in Table 6. Note that with

EEPROM, capacitors are selected when bits are active LOW.

Table 6 – Data writing sequence for EEPROM

Step

Action

1

Determine the desired capacitor control word with the operational power supply voltage and

desired oscillator conditions

2

3

If EEPROM is not already erased, erase EEPROM (see

ERASING THE EEPROM

)

4

Read the current state of the EEPROM bits (see READING BACK FROM THE EEPROM)

5

Compare the desired control word to the stored EEPROM control word. Count the number of

differences so as to prevent double/redundant writing

6

One bit at a time, load the first desired control word bit (bit selection for EEPROM is active LOW)

7

Set the PV pin to +6V (≥5.6V, ≤6.1V) with the pulse and idle shown in timing diagram (Figure 10)

8

Progress through all necessary control word bits by repeating steps 5 & 6 until all bits are set to the

desired control word.

9

Verify the correct EEPROM contents by reading back the individual bits