AD9736BBC datasheet(28/42 Pages) AD

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AD9736/AD9735/AD9734

Preliminary Technical Data

Rev. PrJ | Page 28 of 42

AD9736 ANALOG CONTROL REGISTER

The AD9736 includes some registers for optimizing its analog

performance. These registers include temperature trim for the

bandgap, noise reduction in the output current mirror and output

current mirror headroom adjustments.

BANDGAP TEMPERATURE CHARACTERISTIC TRIM BITS

Using TRMBG<2:0> (REG14, bits 2:0) the temperature

characteristic of the internal bandgap can be trimmed to minimize

the drift over temperature as shown in Figure 31.

Figure 31. BANDGAP Temperature Characteristic for Various TRMBG Values

It is important to note that the temperature changes are sensitive to

process variations and the above plot may not be representative of

all fabrication lots. Optimum adjustment requires measurement of

the device operation at two temperatures and development of a

trim algorithm to program the correct TRMBG<2:0> values in

external non-volatile memory.

MIRROR ROLL OFF FREQUENCY CONTROL

With MSEL<1:0> (REG14, bits 7:6) the user can adjust the noise

contribution of the internal current mirror to optimize the 1/F

noise. Figure 32 shows MSEL vs. the 1/F noise with 20mA Full-

Scale current into a 50ohm resistor.

Figure 32. 1/F Noise With Respect to MSEL Bits

HEADROOM BITS

HDRM<7:0> (REG15, bits 7:0) is for internal evaluation and it is

not recommended to change them from their default reset values.

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