AD8364ACPZ-R2 datasheet(22/44 Pages) AD

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AD8364

Data Sheet

Rev. C | Page 22 of 44

MEASUREMENT CHANNEL DIFFERENCE OUTPUT

USING OUT[P, N]

The AD8364 incorporates two operational amplifiers with rail-

to-rail output capability to provide a channel difference output.

As in the case of the output drivers for OUT[A, B], the output

stages have the capability of driving 70 mA. The output noise is

approximately 40 nV/√Hz at 100 kHz. OUTA and OUTB are

internally connected through 1 kΩ resistors to the inputs of each

operational amplifier. The pin VLVL is connected to the positive

terminal of both operational amplifiers through 1 kΩ resistors to

provide level shifting. The negative feedback terminal is also made

available through a 1 kΩ resistor. The input impedance of VLVL

is 1 kΩ and FBK[A, B] is 2 kΩ. See Figure 59 for the

connections of these pins.

CHANNEL A

TruPwr™

CHANNEL B

TruPwr™

VPSA

VPSB

INHB

INLB

COMR

PWDN

INLA

INHA

VSTA

VSTB

OUTB

FBKB

OUTN

OUTP

FBKA

OUTA

BIAS

TEMP

OUTA

OUTB

ISIG2

ITGT2

VGA

CONTROL

VGA

CONTROL

ISIG2

ITGT2

Figure 59. Operational Amplifier Connections (All Resistors are 1 kΩ ± 20%)

If OUTP is connected to FBKA, then OUTP is given as

OUTP = OUTA – OUTB + VLVL

(9)

If OUTN is connected to FBKB, then OUTN is given as

OUTN = OUTB – OUTA + VLVL

(10)

In this configuration, all four measurements, OUT[A, B, P, N],

are made available simultaneously. A differential output can be

taken from OUTP − OUTN, and VLVL can be used to adjust

the common-mode level for an ADC connection.

CONTROLLER MODE

The channel difference outputs can be used for controlling a

feedback loop to the AD8364 RF inputs. A capacitor connected

between FBKA and OUTP forms an integrator, keeping in mind

that the on-chip 1 kΩ feedback resistor forms a zero. (The value

of the on-chip resistors can vary as much as ±20% with manufac-

turing process variation.) If Channel A is driven and Channel B

has a feedback loop from OUTP through a PA, then OUTP

integrates to a voltage value such that

OUTB = (OUTA + VLVL)/2

(11)

The output value from OUTN may or may not be useful. It is

given by

OUTN = 0 V

(12)

For VLVL < OUTA/3,

Otherwise,

OUTN = (3 × VLVL – OUTA)/2

(13)

If VLVL is connected to OUTA, then OUTB is forced to equal

OUTA through the feedback loop. This flexibility provides the

user with the capability to measure one channel operating at a

given power level and frequency while forcing the other channel

to a desired power level at another frequency. ADJA and ADJB

must be set to different voltage levels to reduce the temperature

drift of the output measurement. The temperature drift will be

statistical sum of the drift from Channel A and Channel B. As

stated before, VLVL can be used to force the slaved channel to

operate at a different power than the other channel. If the two

channels are forced to operate at different power levels, then

some static offset occurs due to voltage drops across metal

wiring in the IC.

If an inversion is necessary in the feedback loop, OUTN can be

used as the integrator by placing a capacitor between OUTN

and OUTP. This changes the output equation for OUTB and

OUTP to

OUTB = 2 × OUTA − VLVL

(14)

For VLVL < OUTA/2,

OUTN = 0 V

(15)

Otherwise,

OUTN = 2 × VLVL – OUTA

(16)

The previous equations are valid when Channel A is driven and

Channel B is slaved through a feedback loop. When Channel B

is driven and Channel A is slaved, the above equations can be

altered by changing OUTB to OUTA and OUTN to OUTP.

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