TQ5135 データシートの表示（PDF） - TriQuint Semiconductor

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TQ5135

3V Cellular CDMA/AMPS LNA/Mixer Receiver IC

TriQuint Semiconductor 

TQ5135

Data Sheet

GND

RF In TQ5135

GND

LNA

Bias

MXR

In

GND

VDD

LO

In

Vdd

IFout

Vdd

Minimize These

Lengths

Figure 2. Critical signal Paths

Mixer – Filter Interaction:

Before attempting a new TQ5135 application, it is important to

understand the nonlinear interaction between the image filter

and the mixer. The device IP3 is a strong function of this

interaction. For this reason it is helpful to consider the filter

and mixer as one nonlinear block.

Figure 3 shows a much simplified block diagram of the LNA,

image filter, and mixer. The RF signal is amplified by the

LNA, passes through the image filter, and is converted down

to the IF where it is amplified by the IF output FET. The

quiescent current in the IF amplifier is set by the GIC network.

Both the filter and the mixer terminate the RF signal with

50ohms.

However, the situation is much different with the LO signal. At

the LO frequency the image filter looks like a short circuit.

Some LO energy leaks out of the mixer input, bounces back

off of the image filter and returns back into the mixer with

some phase or delay. The delayed LO signal mixes with the

normal LO to create a DC offset which is fed into the IF

amplifier and changes the quiescent current. Depending on

the phase of the reflected LO, the IF stage current may be

higher or lower.

The DC offset also affects the passive mixer FET to some

degree as well. It has been found empirically that varying the

delay between the filter and mixer can have positive or

negative consequences on IP3, CG, and NF. It is for this

reason that an LC network is useful between the SAW and

mixer input, even though the mixer input can have an

adequate match at the RF frequency without any external

components.

25-100 ohms at RF-

short circuit at LO

Mixer Portion

of TQ5135

RF in

2

LNA Portion

of TQ5135

LNA Out

14

band pass

LO Leakage

Mixer

IF Output

FET IF Output

12

7

LO Leakage ( φ )

Mixer in

IF + DC

Offset

Idd + Idd Offset

LO

to GIC

9

8

(LO Leakage( φ)+ LO) = DC Offset

at Mixer IF Output

Figure 3. Non-linear filter-Mixer Interaction

10

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