AD8361ART datasheet(12/24 Pages) AD

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AD8361

Rev. C | Page 12 of 24

APPLICATIONS

Basic Connections

Figure 36 through Figure 38 show the basic connections for the

AD8361’s MSOP version in its three operating modes. In all

modes, the device is powered by a single supply of between

2.7 V and 5.5 V. The VPOS pin is decoupled using 100 pF and

0.01 µF capacitors. The quiescent current of 1.1 mA in

operating mode can be reduced to 1 µA by pulling the PWDN

pin up to VPOS.

A 75 Ω external shunt resistance combines with the ac-coupled

input to give an overall broadband input impedance near 50 Ω.

Note that the coupling capacitor must be placed between the

input and the shunt impedance. Input impedance and input

coupling are discussed in more detail below.

The input coupling capacitor combines with the internal input

resistance (Figure 37) to provide a high-pass corner frequency

given by the equation

With the 100 pF capacitor shown in Figure 36 through Figure 38,

the high-pass corner frequency is about 8 MHz.

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

Ω

0.01

µF

100pF

CFLTR

100pF

+VS 2.7V – 5.5V

RFIN

V rms

Figure 36. Basic Connections for Ground Reference Mode

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

Ω

0.01

µF

100pF

CFLTR

100pF

+VS 2.7V – 5.5V

RFIN

V rms

Figure 37. Basic Connections for Internal Reference Mode

AD8361

VPOS

IREF

RFIN

PWDN

SREF

VRMS

FLTR

COMM

Ω

0.01

µF

100pF

CFLTR

100pF

+VS 2.7V – 5.5V

RFIN

V rms

Figure 38. 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 modes of operation

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

reference mode shown in Figure 36, 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 37), the output

voltage swing is shifted upward by an internal reference voltage

of 350 mV. In supply referenced mode (Figure 38), an offset

voltage of VS/7.5 is added to the output voltage. Table 4

summarizes the connections, output transfer function, and

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

Output Swing

Figure 39 shows the output swing of the AD8361 for a 5 V

supply voltage for each of the three modes. It is clear from

Figure 39 that operating the device in either internal reference

mode or supply referenced mode reduces 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 reduces further as

headroom decreases. Figure 40 shows the response of the

AD8361 to a CW input for various supply voltages.

INPUT (V rms)

5.0

4.5

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 39. Output Swing for Ground, Internal, and

Supply Referenced Mode, VPOS = 5 V (MSOP Only)

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