dependency of the external detector diodes is cancelled.

(Adding the temperature correction to the non-inverting ter-

minal is identical to subtracting the temperature correction

from the inverting terminal). The 10µA current sinks con-

nected to the signal paths for VfA, VfB, and TC provide a

bias current for the detector and temperature compensation

diodes. An approximate 200mV deadband for the Ramp

signal is preset.

Ramp Signal

The Ramp signal, which is positive going and ground refer-

enced, is the reference for the closed loop RF output control.

The Ramp signal is smoothed by internal filter with a corner

frequency of approximately 1.6MHz, formed from a 20k

Ω

resistor and 5pF capacitor. This filter eliminates step discon-

tinuities at the baseband DAC’s output. Transconductance

amplifier A2 provides current sinking proportional to the

Ramp signal.

Since the output of A2 connects to the inverting terminal of

A1, A1 draws current from VfA or VfB through the 48.5k

Ω

series resistance previously mentioned. This reduces the

voltage seen at the inverting terminal by the voltage drop

across the 48.5k

Ω series resistance. The transconductance

of A2 is 1/(20k

Ω). The net differential signal between the

non-inverting and inverting terminals of the error amplifier is

2.42 x Ramp-(Vf-TC). This means that the average (Vf-TC)

will be regulated to 2.42 x Ramp and that we want to choose

the RF directional coupler so that the peak RF detector

output at the maximum Ramp satisfies: (Peak Vf)-TC

≤ 2.42

x (maximum Ramp). See “Selecting Coupler/Detector” in the

next section. Note that the recommended maximum Ramp

≤ 2V.

V

HOME

Amplifier A3 and the diode D1 at its output clamp the low

value of the active output to the value set by V

ever the outputs are enabled by Tx_En. V

the inverting input of amplifier A3. The non-inverting input of

amplifier A3 connects to the active output selected by BS,

selection being done by analog switches. Also connecting to

the non-inverting input of amplifier A3 is a voltage divider.

This makes the equation for the minimum output voltage 3.0

xV

Outputs

The output amplifiers A4 and A5 are rail-to-rail complemen-

tary MOS output stages using Class AB control, and capable

of both sourcing and sinking current. The output amplifier not

selected by BS is disabled; both output amplifiers are dis-

abled when Tx_En is low. This conserves power.

The

single

compensation/stabilization

network

across

Comp1 and Comp2 is switched across the correct output

amplifier by analog switches controlled by BS.

Typical LMV248 Configurations:

10137211

FIGURE 3. One Input, One Output (A)

10137212

FIGURE 4. One Input, One Output (B)

10137213

FIGURE 5. One Input, Two Outputs

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