AD8361

–10–

REV. A

With the 100 pF capacitor shown in Figures 32–34, the high-

pass corner frequency is about 8 MHz.

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

100pF

R1

75

CFLTR

1

2

3

45

6

7

8

0.01 F

100pF

RFIN

V rms

Figure 32. Basic Connections for Ground Referenced Mode

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

100pF

R1

75

CFLTR

1

2

3

45

6

7

8

0.01 F

100pF

RFIN

V rms

Figure 33. Basic Connections for Internal Reference Mode

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

100pF

R1

75

CFLTR

1

2

3

45

6

7

8

0.01 F

100pF

RFIN

V rms

Figure 34. Basic Connections for Supply Referenced Mode

The output voltage is nominally 7.5 times the input rms voltage

(a conversion gain of 7.5 V/V rms). Three different modes of

operation are set by the pins SREF and IREF. In addition to the

ground referenced mode shown in Figure 32, where the output

voltage swings from around near ground to 4.9 V on a 5.0 V

supply, two additional modes allow an offset voltage to be added to

the output. In the internal reference mode, (Figure 33), the

output voltage swing is shifted upward by an internal reference

voltage of 350 mV. In supply referenced mode (Figure 34), an

summarizes the connections, output transfer function and mini-

mum output voltage (i.e., zero signal) for each mode.

Output Swing

Figure 35 shows the output swing of the AD8361 for a 5 V supply

voltage for each of the three modes. It is clear from Figure 35,

that operating the device in either internal reference mode or

supply referenced mode, will reduce the effective dynamic range as

the output headroom decreases. The response for lower supply

voltages is similar (in the supply referenced mode, the offset is

smaller), but the dynamic range will be reduced further, as head-

room decreases. Figure 36 shows the response of the AD8361 to

a CW input for various supply voltages.

INPUT – V rms

5.0

4.5

0.0

0

0.5

0.1

0.2

0.3

0.4

3.0

1.5

1.0

0.5

4.0

3.5

2.0

2.5

SUPPLY REF

INTERNAL REF

GROUND REF

0.6

0.7

0.8

Figure 35. Output Swing for Ground, Internal and Supply

Referenced Mode. VPOS = 5 V (micro_SOIC Only)

INPUT – V rms

5.5

1.5

0

0.5

0.1

0.2

0.3

0.4

4.0

3.0

2.5

2.0

5.0

4.5

3.5

1.0

0.5

0.0

5.5V

5.0V

3.0V

2.7V

0.6

0.7

0.8

Figure 36. Output Swing for Supply Voltages of 2.7 V,

3.0 V, 5.0 V and 5.5 V (micro_SOIC Only)

Dynamic Range

Because the AD8361 is a linear responding device with a nomi-

nal transfer function of 7.5 V/V rms, the dynamic range in dB is

not clear from plots such as Figure 35. As the input level is

increased in constant dB steps, the output step size (per dB)

will also increase. Figure 37 shows the relationship between the

output step size (i.e., mV/dB) and input voltage for a nominal

transfer function of 7.5 V/V rms.

Table I. Connections and Nominal Transfer Function for

Ground, Internal, and Supply Reference Modes

Output

Reference

Intercept

Mode

IREF

SREF

(No Signal)

Output

Ground

VPOS

COMM

Zero

Internal

OPEN

COMM

0.350 V

Supply

VPOS

VPOS