AD8342

Rev. 0 | Page 18 of 20

HIGH IF APPLICATIONS

In some applications it may be desirable to use the AD8342 as

an up-converting mixer. The AD8342 is a broadband mixer

capable of both up and down conversion. Unlike other mixers

that rely on on-chip reactive circuitry to optimize performance

over a specific band, the AD8342 is a versatile general-purpose

device that can be used from arbitrarily low frequencies to sev-

eral GHz. In general, the following considerations help to en-

sure optimum performance:

• Minimize ac loading impedance of IF port bias network.

• Maximize power transfer to the desired ac load.

•

For maximum conversion gain and the lowest noise per-

formance reactively match the input as described in the

IF Port section.

• For maximum input compression point and input intercept

points resistively terminate the input as described in the

IF Port section.

As an example, Figure 51 shows the AD8342 as an up-

converting mixer for a WCDMA single-carrier transmitter de-

sign. For this application, it was desirable to achieve −65 dBc

adjacent channel power ratio (ACPR) at a −13 dBm output

power level. The ACPR is a measure of both distortion and

noise carried into an adjacent frequency channel due to the

finite intercept points and noise figure of an active device.

8

7

6

13

15

16

COMM

IFOP

IFOM

5

COMM

14

2

1

3

4

COMM

RFCM

RFIN

VPMX

VPDC

PWDN

EXRB

COMM

11

12

10

9

VPLO

LOCM

LOIN

COMM

AD8342

VPOS

VPOS

34nH

34nH

100pF

100pF

1nF

1nF

ETC1-1-13

100pF

100pF

0.1

µF

VPOS

1nF

1nF

1970MHz

OSC

1.82k

Ω

100pF

4.7pF

170MHz

INPUT

100nH

1nF

499

Ω

VPOS

100pF

0.1pF

2140MHz OUT

1nF

Figure 51. WCDMA Tx Up-Conversion Application Circuit

Because a WCDMA channel encompasses a bandwidth of

almost 5 MHz, it is necessary to keep the Q of the matching

circuit low enough so that phase and magnitude variations are

below an acceptable level over the 5 MHz band. It is possible

to use purely reactive matching to transform a 50 Ω source

to match the raw ~1 kΩ input impedance of the AD8342.

However, the L and C component variations could present

production concerns due to the sensitivity of the match. For

this application, it is advantageous to shunt down the ~1 kΩ

input impedance using an external shunt termination resistor

to allow for a lower Q reactive matching network. The input is

terminated across the RFIN and RFCM pins using a 499 Ω

termination. The termination should be as close to the device as

possible to minimize standing wave concerns. The RFCM is

bypassed to ground using a 1 nF capacitor. A dc blocking ca-

pacitor of 1 nF is used to isolate the dc input voltage present on

the RFIN pin from the source. A step-up impedance transfor-

mation is realized using a series L shunt C reactive network.

The actual values used need to accommodate for the series L

and stray C parasitics of the connecting transmission line seg-

ments. When using the customer evaluation board with the

components specified in Figure 51, the return loss over a 5 MHz

band centered at 170 MHz was better than 10 dB.

External pull-up choke inductors are used to feed dc bias into

the open-collector outputs. It is desirable to select pull-up choke

inductors that present high loading reactance at the output

frequency. Coilcraft 0302CS series inductors were selected due

to their very high self-resonant frequency and Q. A 1:1 balun

was ac-coupled to the output to convert the differential output

to a single-ended signal and present the output with a 50 Ω

ac loading impedance.

The performance of the circuit is shown in Figure 52. The aver-

age ACPR of the adjacent and alternate channels is presented

vs. output power. The circuit provides a 65 dBc ACPR at

−13 dBm output power. The optimum ACPR power level can be

shifted to the right or left by adjusting the output loading and

the loss of the input match.

–60

–70

–25

0

OUTPUT POWER (dBm)

–62

–64

–66

–68

–20

–15

–10

–5

ADJACENT

CHANNELS

ALTERNATE

CHANNELS

Figure 52. Single Carrier WCDMA ACPR Performance of Tx Up-Conversion

Circuit (Test Model 1_64)