AD831

REV. B

–10–

The RF input to the AD831 is shown connected by an imped-

ance matching network for an assumed source impedance of

50

Ω. Figure 15 shows the input impedance of the AD831 plot-

ted vs. frequency. The input circuit can be modeled as a resis-

connected from IFN and IFP to VP provide a low-pass filter

with a cutoff frequency of approximately 140 MHz in down-

conversion applications (see the Theory of Operation section of

this data sheet for more details). The LO input is connected

single-ended because the limiting amplifier provides a symmet-

ric drive to the mixer. To minimize intermodulation distortion,

connect pins OUT and VFB by the shortest possible path. The

connections shown are for unity-gain operation.

At LO frequencies less than 100 MHz, the AD831’s LO power

may be as low as –20 dBm for satisfactory operation. Above

100 MHz, the specified LO power of –10 dBm must be used.

51.1

Ω

110

Ω

IF

OUTPUT

BPF

NC

–5V

0.1µF

0.1µF

+5V

51.1

Ω

0.1µF

+5V

–5V

0.1µF

–5V

0.1µF

C2

L1

C1

RF

INPUT

82pF

82pF

0.1µF

+5V

IFN

VP

IFP

AP

GND

VN

RFP

RFN

VN

VP

LON

LOP

VP

GND

BIAS

VN

AD831

Top View

50

Ω

50

Ω

6

7

8

4

5

9

10

11

12

13

AN

VFB

COM

OUT

14

15

16

17

18

1

2

3

19

20

LO INPUT

–10 dBm

Figure 25. Connections for

±5 V Dual-Supply Operation Showing Impedance

Matching Network and Gain of 2 for Driving Reverse-Terminated IF Filter

APPLICATIONS

Careful component selection, circuit layout, power supply

decoupling, and shielding are needed to minimize the AD831’s

susceptibility to interference from radio and TV stations, etc. In

bench evaluation, we recommend placing all of the components

in a shielded box and using feedthrough decoupling networks

for the supply voltage.

Circuit layout and construction are also critical, since stray ca-

pacitances and lead inductances can form resonant circuits and

are a potential source of circuit peaking, oscillation, or both.

Dual-Supply Operation

Figure 25 shows the connections for dual supply operation.

Supplies may be as low as

±4.5 V but should be no higher than

±5.5 V due to power dissipation.