PIN diode Vector Modulators -

Fundamentals and Drive Requirements

Rev. V4

Application Note

AN3001

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2

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Amplitude Ripple: This is one half of the peak-to-peak

ripple in the specified frequency band. For example, if

the minimum loss is 11.8 dB, and the maximum loss

is 12.2 dB, the peak to peak ripple is 0.4 dB, so the

Amplitude Ripple would be 0.2 dB.

Deviation from Linear Phase:

This is a test to see

how linear the phase of the vector modulator is. To

find Deviation from Linear Phase, a line that best

approximates the measured data points by using the

method of least squares must be found.

The

deviation from linear phase is the difference between

the calculated and measured line.

Drive Requirements for a Vector Modulator

Driving

a

vector

modulator

requires

a

solid

understanding of the transfer function from the Bias1

and Bias2 inputs to the amplitude and phase change

of the vector modulator. It should be noted that vector

modulators are driven by current, due to the PIN

diode construction.

The following description will

focus on how PIN diode vector modulators are driven

by dual linearizers. A chart of the drive characteristics

when driven by current will also be provided.

M/A-COM

has

designed

a

dual

linearizer,

MADRCC0002, so that the amplitude and phase of

the vector modulators is linearized relative to the

control voltages at the inputs of the linearizer. See

the

circuit

in

Figure

3

for

the

schematic

of

MADRCC0002

driving

the

SA90-0001

vector

modulator.

This same schematic also holds when

driving the MAMDCC0002 and MAMDCC0005 vector

modulators.

The first step is to determine the reference loss of the

vector modulator. See Figure 4, which provides the

transfer function of the test.

Figure 1. Block Diagram

Figure 2. Summation of Vectors

0°

A

180°

A

90°

B

-90°

B

1

1

1* 2

The four outer curves are found by sweeping the bi-

ases as follows:

1.

Set Bias2 to 0.0V. Sweep Bias1 from 0.0 to 5.0V

in 0.1V increments.

2.

Keep Bias1 at 5.0V.

Sweep Bias2 from 0.0 to

5.0V in 0.1V increments.

3.

Keep Bias2 at 5.0V.

Sweep Bias1 from 5.0 to

0.0V in 0.1V increments.

4.

Keep Bias1 at 0.0V.

Sweep Bias2 from 5.0 to

0.0V in 0.1V increments.

The circle that is tangent to the inside of the plot is the

reference loss circle, which is about 12 dB in this ex-

ample. Note that the plots in Figures 4 and 5 are the

same, but the lines of different bias voltages were

removed to clarify the curves that are used to find

reference loss. Figures 5 and 6 use the same axes

and scales. The tick marks on the axes are reflection

coefficients in steps of 0.1. The equation that calcu-

lates loss from reflection coefficient is:

Mag = 10^(loss_in_dB/20)

Figure 5 provides a plot of insertion loss (in magni-

tude) and phase as the control inputs are varied in

0.5V increments from 0.0V to 5.0V. This gives a good

representation of the loss and phase.

However, it

should be noted that this plot will vary lot to lot. The

primary reason for the variation is that the resistance

vs. current of PIN diodes had some lot to lot variation.

Both graphs in Figure 5 have the same data. Due to

the number of labels, the plot was repeated to ensure

legibility.

Figure 6 is similar to Figure 5, but is a plot of insertion

loss (in magnitude) and phase vs. control current.