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ATR0797

4665D–SIGE–08/04

Product Description

Atmel’s ATR0797 is a variable gain I-Q demodulator designed for use in receiver IF sec-

tions, that are typically existing in superheterodyne RF architectures.

The ATR0797 has two gain stages that are independent of each other. These gain

stages are broadband differential amplifiers each with a digital control pin to set the

gain. Since the amplifiers have approximately the same gain, setting GC1 high and GC2

low results in approximately the same gain as setting GC1 low and GC2 high. Former

setting offers better noise figures.

The IF input is a differential input that has internal bias circuitry to set the common mode

voltage. The use of blocking capacitors to facilitate AC coupling is highly recommended

to avoid changing the common mode voltage. Either input may be driven single ended if

the other input is connected to ground through an AC short such as a 1000 pF capacitor.

This typically results in slightly lower input P1dB.

The two matched mixers are configured with the quadrature LO generator to provide in-

phase and quadrature baseband outputs.

The LO and IF ports offer a differential 50

Ω impedance. The passives at these ports

(parallel L-R network) and the package itself adds inductance that tends to degrade

return loss.

The ATR0797 features immunity from changes in LO power. The gain features change

by less than 0.6 dB over a 6 dB range of LO power. Also note the excellent I/Q balance,

which typically falls within 0.1 dB and 1 degree from 65 MHz to 300 MHz, and varies

less than 0.05 dB and 0.5 degree over temperature (-40°C to +85°C).

The frequency response of the IF and LO ports is dominated by the L-R network on the

input. When de-embedded, the gain and P1dB response is within 0.5 dB from 65 MHz to

300 MHz.

The figures in the datasheet illustrate a typical ATR0797’s performance with respect to

temperature. Note that these numbers include the effect of the R-L network in the IF

port.

Evaluation board design and equipment constraints:

Please take into account that the evaluation board uses baluns on the I/Q outputs, and

these baluns limit the low frequency response of the device. For true baseband opera-

tion, the baluns should be removed, and the differential signals used directly.

The 27 pF capacitor on the evaluation board is appropriate for lower frequencies.