TQ5631 데이터 시트보기 (PDF) - TriQuint Semiconductor

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TQ5631

3V PCS Band CDMA RFA/Mixer IC

TriQuint Semiconductor 

TQ5631

Data Sheet

the ground end of the shunt cap should be as close to the chip

ground as is possible.

Vdd

bypass

GIC PIN

Chip

GND

GIC PIN

Chip

GND

IF

OUT

L

Cseries

50

ohms

Cshunt

Figure 4 IF Output Match

GIC Component Selection

The GIC pin on the TQ5631 is connected internally to the

source of the IF output stage. By adding two resistors and a

capacitor to this pin, it is possible to vary both the IF stage AC

gain, and the IF stage quiescent current. However, there is a

limit to the amount of gain increase that is possible, since there

always exists some package and bond wire inductance back to

the die. Furthermore, although some additional IP3

performance may be gained by increasing the quiescent current,

in practice it makes no sense to increase Idd beyond that which

provides maximum input intercept. At some point IP3 is limited

by the mixer FET, and no further increase in input intercept can

be obtained by adjusting the IF stage.

There are two GIC schemes that are recommended for the

CDMA devices (Figure 5). The first uses a small resistor in

series with a larger bypassed resistor. The AC gain is set by the

unbypassed resistor, while the DC IF current is then set by the

sum of the two resistors.

The second scheme, which is recommended for the high band

device, uses a resistor in parallel with a series combination of

resistor and capacitor. The first resistor sets the DC current,

while the equivalent parallel resistance sets the AC gain. The

presence of a resistor directly from the GIC pin to ground tends

to dampen the Q of any resonance in the 5-10ghz range which

might be formed by the GIC circuitry.

0 to 5 ohms AC degen

Zc bypass

at IF Freq

20 to 60 ohms

sets IF

current

20 to 60 ohms

sets IF

current

0 to 5 ohms

AC degen

Zc bypass

at IF Freq

Minimize Board

Ground

Return Inductance

Figure 5 GIC Pin Networks

Minimize Board

Ground

Return Inductance

The Image Filter to Mixer RF input Path

We recommend evaluating the CDMA downconverter by

considering it and the image filter as a block, since there is a

very complicated non-linear interaction between the mixer and

image filter. Especially in the LG and MG receiver modes, some

LO energy leaks out through the RF input, reflects off the image

filter, and then returns back into the mixer (Figure 6).

The reflection at the filter occurs because most SAW and

dielectric filters look like a short circuit outside of the passband.

Depending on the phase of the reflected signal, noise figure,

gain, and IP3 can be negatively affected. Thus system

simulation can be inaccurate if the downconverter and filter are

treated separately.

LO Leakage

band pass

LO Leakage + φ

LNA in Bypass

Mode

Mixer

IF

LO

Figure 6 Mixer-Filter Interaction

The issue also raises a dilemma with regard to the specification

of SSB noise figure. An image filter is needed for measurement;

yet how does one go about specifying the SSB noise figure (CG

10

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

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