Philips Semiconductors

Product specification

NE/SA600

1GHz LNA and mixer

1993 Dec 15

58

the NE/SA600 mixer with the net IF impedance equal to 500

Ω.

It is more common to express the conversion gain in terms of power,

so we have the Power Conversion Gain,

PG

P

A

P

I

* 3dB

the mixer RF port. With a 500

Ω 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

THEORY OF OPERATION

The NE/SA600 is fabricated on the Philips Semiconductors

advanced QUBiC technology that features 1

µm 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) 0.01

µF is used. The inputs and outputs are matched to

50

Ω. 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

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 50

Ω 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 50

Ω 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

supplies the LNA and powers overhead circuitry. Typical current

draw is 9.8mA while enable is high (1mA powered down). The Pin

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

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

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.