ADMV1455BBCZ-R7 datasheet(73/141 Pages) AD

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Data Sheet

ADMV1455

THEORY OF OPERATION

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GAIN LUT

The digital logic contains a gain LUT with 67 indices that can be

used to determine the state of the DSAs and the GPO_G logic

outputs. This LUT can be beneficial for fast frequency hopping

applications, where it may be necessary to quickly change the chip

configuration states.

To use the LUT, set Register 0x285 to 1 and setup the LUT from

There are three potential sources for the LUT index (pointer), as

determined by Register 0x286. The pointer can be set by using the

parallel logic input ADD_G balls, by using Register 0x282, or by

using the internal state machine. Set Register 0x286 to 0 to use

ADD_G balls as the pointer, set Register 0x286 to 1 to use Register

0x282 as the pointer, and set Register 0x286 to 2 to use the internal

state machine.

Regardless of LUT pointer source, use Register 0x298 to read back

the pointer value.

The LUT output values can be read from Register 0x28F to Regis-

ter 0x290. The values in these registers represent the DSA values

prior to the mux controlled by Register 0x285 and the LOAD

feature.

Gain State Machine

The internal state machine can be used to sequence through many

states, using the ADD_G5 input to advance and ADD_G4 to reset.

The state machine has several input parameters from the SPI, such

as offset value, stop value, step size, and reset.

At power up, the state machine output is zero, and it can be reset to

zero using either the ADD_G4 ball or Register 0x287. Set ADD_G4

to logic high to hold the state machine in reset and then bring to

logic low to re-enter normal operation. Alternatively, set Register

0x287 to 0 to hold the state machine in reset and then set it back to

1 to re-enter normal operation.

The step size is a 8-bit twos complement value, with a range

of −128 to +127, where −128 is represented by 0x80, +127 is

represented by 0x7F, and −1 is represented by 0xFF. A step size of

zero is invalid.

The state machine increments or decrements on each rising edge

of ADD_G5 based upon the step size value programmed. The

state machine is always bound by zero and the stop value. Once

it has reached one of these bounds, it remains there. When the

state machine value is equal to the stop value, changing the step

size from a positive number to a negative number allows the state

machine to be decremented back to zero.

The offset value is a 8-bit twos complement value, with a range

of −128 to +127, where −128 is represented by 0x80, +127 is

represented by 0x7F, and −1 is represented by 0xFF.

The pointer value is equal to the state machine value plus the offset

value. Use Register 0x288 to read back the current value of the

pointer.

Both the state machine value and the pointer value are bound by

zero and the stop value. If the state machine is left at a particular

value and the stop value or offset value is changed, then the pointer

may update provided it is within these bounds. The minimum

pointer value is bound by the offset value or zero, which ever is

greater.

Refer to Table 19 for the applicable registers and example state

machine behavior. The sequences shown in Table 19 continue do

not continue indefinitely for each rising edge on ADD_G5. The state

machine must be reset, the step size changed, or the stop value

changed to allow additional sequencing after it has reached the end

of a sequence.

Table 19. Gain State Machine Example Behavior

Example

Step1

Offset2

Stop3

State Machine Sequence

0, 1, 2, 3, 4, 5, 6

0, 2, 4, 6

0, 4, 6

0, 6

1, 2, 3, 4, 5, 6

1, 3, 5, 6

1, 4, 6

-1

6, 5, 4, 3, 2, 1, 0

1 The step size is determined by Register 0x283, Bits[7:0].

2 The offset is determined by Register 0x284, Bits[7:0].

3 The stop is determined by Register 0x289, Bits[6:0].

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