TQ9222 데이터 시트보기 (PDF) - TriQuint Semiconductor

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TQ9222

Dual-Band TDMA LNA/Downconverter IC

TriQuint Semiconductor 

10pF

Mx IF

Pin 14

8.2pF out

180nH

Vdd

0.01uF 10Ω

Note: These values assume ideal components and neglect board parasitics.

The discrepancy between these values and those of the typical application

circuit are the board and component parasitics

TQ9222

Data Sheet

that the length of the transmission line in the filter input also has

an effect on Half-IF performance.

700 mils from pin

to filter input

Fig. 8 Suggested IF Match

Half-IF Application

When the intermediate frequency is less than twice the

bandwidth of the receiver, Half-IF intermodulation spurs will fall

within the frequency of operation. The image filter and mixer are

the main circuit blocks that influence Half-IF spur suppression.

However, it was shown experimentally that the preselector filter

plays an important role as well in suppressing half-IF and image

spurious signals. The preselector filter eliminates out of band

spurs that could get amplified and degrade the performance.

A narrow band pass filter and a high IF frequency are best to

eliminate Half-IF problems. The other major contribution is mixer

balance which is affected by two factors. First, the LO signal that

leaks into the mixer inputs via parasitics. The second major

contribution is the source impedance presented at the mixer RF

input port. Depending on the board layout, the optimum mixer

source impedance may shift which will degrade the Half-IF

performance.

It is possible to optimize mixer source impedance for Half-IF

rejection at the LO frequency only. This will avoid affecting the

desired signal to a large degree. Experience with the TQ9222,

has shown that optimum mixer source impedance results in a

significant mismatch causing gain reduction. Therefore, a trade-

off has to be made between optimum Half-IF performance and

conversion gain.

The standard TQ9222 evaluation board uses a Toko TDFM1B-

1960L-11 dielectric filter in the high band. It was found that an L-

network, comprised of a series 1.8 nH inductor and a shunt 1.8

pF capacitor on the mixer input, produces the best Half-IF

rejection and conversion gain. To a lesser extent, it was found

23

22

1.8pF

21

1.8nH

Fig. 9 Image and Half-IF circuit

Note that if the final board layout is significantly different from

our evaluation board, the network shown will only be useful as a

guideline for development or to show what performance is

possible with the TQ9222. A SAW filter will probably require a

totally different type of network; and network component values

vary widely between SAW filter models.

Usually only a portion of the frequency band will be of concern

for half-IF interference. It will depend on the injection mode of

the LO signal and the IF frequency being used. For example If

the LO is a high side injection such as the case of the TQ9222

and the IF = 110 MHz then (theoretically) we worry about the

first 5 MHz of the band (1930-1935) only if we have ideal filters.

Unfortunately most of the image stripping filters roll-off around

2000 MHz or higher hence the need to optimize performance up

to 1945 MHz. The opposite occurs for low side LO.

Since the frequency response of the preselector and image

stripping filter help the performance at the high end of the band,

the TQ9222 was tuned to give good half-IF rejection at the low

end of the band over a wide temperature range (-40 °C to +85

°C). That was accomplished with a Pi-network* (between the

filter output and the mixer input) comprise of a series L = 2.2

nH, shunt C = 1.0 and 0.5 pF. As expected this tuning network

degraded the half-IF performance from 1970 to 1990 MHz

specially at the extremes temperatures. However, once the

For additional information and latest specifications, see our website: www.triquint.com

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