uaa1570hl NXP Semiconductors, uaa1570hl Datasheet - Page 22

• Manufacturer Part Number: uaa1570hl
• Description: Global Positioning System Gps Front-end Receiver Circuit
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.3
The 1st mixer (the RF mixer) consists of an RF
preamplifier followed by a Gilbert cell mixer. The RF
preamplifier consists of the same unbalanced common
emitter and cascode stage as used in the LNAs, but
without the compound feedback bootstrap output stage.
The cascode output is AC-coupled into one side of the
lower tree of the Gilbert cell mixer. The other side is
internally AC-coupled to mixer ground via a 20 pF
decoupling capacitor. The Gilbert mixer RF input is
degenerated with low loss inductive emitter feedback to
increase the effective 1 dB compression point and
intercept points. Referenced to the preamplifier input, the
1999 May 10
important first mixer parameter is its 2nd-order input
intercept point, which will extrapolate to approximately
1.38 V (peak value) differential or +12.8 dBm in the 50
mixer input environment.
The differential output of the Gilbert cell mixer is
open-collector to allow optimization of conversion gain and
matching to the first IF filter over a wide range of
frequencies and filter options. The total conversion gain is
therefore determined by the real part of the effective output
load, which is given by the IF filter input impedance and
loss and/or fixed filter input matching networks, if present.
The voltage conversion gain can be estimated by
multiplying the effective single-ended to differential
transconductance value for the first mixer (0.0531 A/V) by
the total effective differential output resistance. The total
power conversion gain to a differential load can be
estimated from the voltage conversion gain by subtracting
the output resistance is distributed between the fixed
output termination, the IF filter input impedance, as well as
equivalent loss impedances associated with the finite Q of
filter components. The assumption has also been made
that the output impedance which the mixer sees is real, at
least in the IF band.
Note: The open-collector outputs of the first mixer each
include internal 4 pF capacitors to ground. These
capacitors should be included in the design of the first IF
filter by removing 2 pF from the differential input
capacitance for balanced filters and 4 pF from
single-ended designs.
10
1 dB compression point and 3rd-order intercept point are
25.4 dBm and 16.3 dBm, respectively. Another
Global Positioning System (GPS) front-end
receiver circuit
log
diff_load
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RF mixer with preamplifier
50
. The total power delivered by the mixer to
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Therefore, the test circuit voltage conversion gain is
estimated at 0.0531 A/V times the effective differential
loading of approximately 440 . This results in a voltage
conversion gain of approximately 27.4 dBV. Subtracting
9.4 dB to convert from power in a 50
power into 440 , we see that the first mixer delivers a
total power conversion gain of approximately 18.0 dB in
the test circuit. It is important to note that approximately
3 dB of this available power gain is lost in the test circuit
output transformer termination and that much of this power
can be recovered in application circuits.
The peak differential output voltage swing of the mixer
should be limited to less than approximately
1 V (peak value) or 2 V (p-p) differential or
0.5 V (peak value) single-ended to prevent clipping by the
internal output ESD protection diodes and to prevent mixer
output saturation. This implies that effective differential
output loads of approximately 2.5 k could result in
clipping at the output of the mixer.
The first mixer output structure also supports single-ended
first IF filter applications. By taking one of the mixer outputs
to the supply rail, the other can drive a single-ended first IF
filter, thereby reducing external component cost in some
applications. Maintaining the same single-ended loading
impedance, as in the differential case (i.e. double the
effective single-ended load) results in the same peak
voltage across the same load, even with only half the
transconductance
same power is delivered to the same filter load and the
conversion gain remains the same. However, an effective
load of 1.25 k would also bring this single-ended mixer
output to the same clipping point as the full differential
equivalent load of 2.5 k . The maximum recommended
first mixer single-sided voltage conversion gain (input to
one output) is therefore approximately 32 for both
single-ended and differential output applications.
The power matched Double-Side Band (DSB) noise figure
of the RF mixer with preamplifier is approximately 12 dB at
1.57542 GHz from a 3 V supply.
1
2
(0.0531 A/V) available. Therefore the
UAA1570HL
Product specification
environment to