SA600 Datasheet, PDF (12/17 Pages) NXP Semiconductors – 1GHz LNA and mixer

Philips Semiconductors
1GHz LNA and mixer
Product specification
NE/SA600
loss (and any other matching required). Typically, VG_C is 10.4dB for
the NE/SA600 mixer with the net IF impedance equal to 500Ω.
It is more common to express the conversion gain in terms of power,
so we have the Power Conversion Gain,
ǒ Ǔ PG_C
+
10 log
P_A
P_I
* 3dB
where P_A = V_A2 / R_IF and P_I = V_I2 / R_RF. R_IF is the net resistance at
the IF frequency at the IF port, and R_RF is the input impedance at
the mixer RF port. With a 500Ω IF impedance and a 50Ω RF input
impedance, the conversion gain works out to –2.6dB typically. The
power delivered to the load is down 3dB with respect to the available
power because of loss in R_L1.
THEORY OF OPERATION
The NE/SA600 is fabricated on the Philips Semiconductors
advanced QUBiC technology that features 1µm channel length
MOSFETs and 13GHz FT bipolar transistors.
LNA
The Low Noise Amplifier (LNA) is a two stage design incorporating
feedback to stablize the amplifier. An external bypass capacitor of
(typically) 0.01µF is used. The inputs and outputs are matched to
50Ω. The amplifier has two gain states: when the ENABLE pin is
taken high, the amplifier draws 9mA of current and has 16dB of gain
at 900MHz. When the ENABLE pin is low, the amplifier current goes
to zero, and the amplifier is replaced by a thru. Typical loss for the
thru is 7dB. This dual-gain state approach can be used in
bang-bang control systems to achieve a low gain, high overload
front-end as well as the more usual high gain, low overload
front-end.
The amplifier has gain to frequencies past 2GHz, but a practical
upper end is 1.6-1.7GHz. Both the input match and the noise figure
(NF) can be improved with a shunt 15-18nH inductor at the input.
Typically, the gain increases 0.4dB, the match improves to 13-16dB,
and the noise figure drops to 1.95-2dB. Variations of any of the RF
parameters with V_CC is negliglible, and variation with temperature is
minimal.
Mixer
The mixer is a single-balanced topology designed to draw very low
current, typically 4mA, and provide a very high input third-order
intermodulation intercept point , typically IP3=+6dBm. The RF and
LO ports impedances are nearly 50Ω resistive, and the IF output is
an open collector. The open-collector output allows direct
interfacing with high impedance IF filters, such as surface acoustic
wave (SAW) filters without the need for external step-up
transformers (which are needed for 50Ω output mixers).
The basic mixer is functional from DC to well over 2.5GHz, but RF
and LO return losses degrade below 100MHz. The IF output can be
used from DC to 500MHz or more, although typically the
intermediate frequency is in the range 45-120MHz in many 900MHz
receivers. To achieve the lowest noise, the LO drive level should be
increased as high as possible, consistent with power dissipation
limitations.
POWER SUPPLY ISSUES
V_CC bypassing is important, but not extremely critical because of
the internal supply regulation of the NE/SA600. The Pin 1 V_CC
supplies the LNA and powers overhead circuitry. Typical current
draw is 9.8mA while enable is high (1mA powered down). The Pin
14 V_CCMX powers the mixer and typically has 3.2mA of current
(assuming an inductor biasing the IFout back to V_CCMX). Care must
be taken to avoid bringing any IC pin above V_CC by more than 0.3V,
or below any ground by more than 0.3V. For example, this can
occur if the enable pin is fed from a microcontroller that is powered
up quicker than the NE/SA600. In this condition the internal
electrostatic discharge (ESD) protection network may turn-on,
possibly causing a part misfunction. Generally this condition is
reversible, so long as the source creating the overstress is current
limited to less than 100mA. To avoid the problem, make sure both
V_CC pins are tied together near the IC, and install a 1kΩ resistor in
series with the enable pin if it is likely to go above V_CC.
BOARD LAYOUT CONSIDERATIONS
The LNA is sensitive to mutual inductance from the input to ground.
Therefore long narrow input traces will degrade the input match.
Ideally, a top side ground-plane should be employed to maximize
LNA gain and minimize stray coupling (such as LO to antenna). To
avoid amplifier peaking, the output and input grounds should not be
run together. Attach both grounds to a solid ground plane. A solid
ground plane beneath the package will maximize gain. Top side to
back side ground through holes are highly recommended.
The mixer is relatively insensitive to grounding. Care should be
taken to minimize the capacitance on the RF port (Pin 11) for best
noise figure. Also, the capacitance on the IFout pin must be kept
small to avoid conversion gain rolloff when using high IF
frequencies. The purpose of the inductor from IFout to V_CC is to set
the midpoint of the IF swing to be V_CC. Without this inductor the
part is sensitive to output overload under low V_CC (V_CC = 4.5V) and
hot temperature conditions. The V_CCMX pin must be kept at the
same potential as the V_CC pin.
APPLICATIONS INFORMATION
The NE/SA600 is a high performance, wide-band, low power, low
noise amplifier (LNA) and mixer circuit integrated in a BiCMOS
technology. It is ideally suited for RF receiver front-ends for both
analog and digital communications systems.
There are several advantages to using the NE/SA600 as a high
frequency front-end block instead of a discrete implementation. First
is the simplicity of use. The NE/SA600 does not need any external
biasing components. Due to the higher level of integration and
small footprint (SO14) package it occupies less space on the printed
circuit board and reduces the manufacturing cost of the system.
Also the higher level of integration improves the reliability of the LNA
and mixer over a discrete implementation with several components.
The LNA thru mode in NE/SA600 helps reduce power consumption
in applications where the amplifiers can be disabled due to higher
received signal strength (RSSI). Other advantages of this feature
are described later in this section.
The mixer is an active mixer with excellent conversion gain at low
LO input levels, so LO levels as low as -5dBm to -10dBm can be
used depending on the applications requirement for mixer gain,
mixer noise figure and mixer third order intercept point. This
reduces the LO drive requirements from the VCO buffer, thus
reducing its current consumption. Also, due to lower LO levels, the
shielding requirements can be minimized or eliminated, resulting in
substantial cost savings and weight and space reduction.
1993 Dec 15
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