Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

853-0594 18663

DESCRIPTION

The SA614A is an improved monolithic low-power FM IF system
incorporating two limiting intermediate frequency amplifiers,
quadrature detector, muting, logarithmic received signal strength
indicator, and voltage regulator. The SA614A features higher IF
bandwidth (25MHz) and temperature compensated RSSI and
limiters permitting higher performance application compared with the
SA604. The SA614A is available in a 16-lead dual-in-line plastic
and 16-lead SO (surface-mounted miniature) package.

FEATURES

Low power consumption: 3.3mA typical

Temperature compensated logarithmic Received Signal Strength
Indicator (RSSI) with a dynamic range in excess of 90dB

Two audio outputs - muted and unmuted

Low external component count; suitable for crystal/ceramic filters

Excellent sensitivity: 1.5

V across input pins (0.22

V into 50

matching network) for 12dB SINAD (Signal to Noise and Distortion
ratio) at 455kHz

SA614A meets cellular radio specifications

PIN CONFIGURATION

D and N Packages

IF AMP DECOUPLING 1

GND

MUTE INPUT

RSSI OUTPUT

MUTE AUDIO OUTPUT

UNMUTE AUDIO OUTPUT

QUADRATURE INPUT

IF AMP INPUT

IF AMP DECOUPLING

IF AMP OUTPUT

GND

LIMITER INPUT

LIMITER DECOUPLING

LIMITER

VCC

SR00323

Figure 1. Pin Configuration

APPLICATIONS

Cellular radio FM IF

High performance communications receivers

Intermediate frequency amplification and detection up to 25MHz

RF level meter

Spectrum analyzer

Instrumentation

FSK and ASK data receivers

ORDERING INFORMATION

DESCRIPTION

TEMPERATURE RANGE

ORDER CODE

DWG #

16-Pin Plastic Dual In-Line Package (DIP)

-40 to +85

SA614AN

SOT38-4

16-Pin Plastic Small Outline (SO) package (Surface-mount)

-40 to +85

SA614AD

SOT109-1

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

AC ELECTRICAL CHARACTERISTICS

Typical reading at T

= 25

C; V

= +6V, unless otherwise stated. IF frequency = 455kHz; IF level = -47dBm; FM modulation = 1kHz with

+8kHz peak deviation. Audio output with C-message weighted filter and de-emphasis capacitor. Test circuit Figure 3. The parameters listed
below are tested using automatic test equipment to assure consistent electrical characterristics. The limits do not represent the ultimate
performance limits of the device. Use of an optimized RF layout will improve many of the listed parameters.

LIMITS

SYMBOL

PARAMETER

TEST CONDITIONS

SA614A

UNITS

MIN

TYP

MAX

Input limiting -3dB

Test at Pin 16

-92

dBm/50

AM rejection

80% AM 1kHz

Recovered audio level

15nF de-emphasis

175

260

RMS

Recovered audio level

150pF de-emphasis

530

RMS

THD

Total harmonic distortion

-30

-42

S/N

Signal-to-noise ratio

No modulation for noise

RF level = -118dBm

160

800

RSSI output

RF level = -68dBm

1.7

2.50

3.3

RF level = -18dBm

3.6

4.80

5.8

RSSI range

= 100k (Pin 5)

RSSI accuracy

= 100k (Pin 5)

+2.0

IF input impedance

1.4

1.6

IF output impedance

0.85

1.0

Limiter input impedance

1.4

1.6

Unmuted audio output resistance

Muted audio output resistance

NOTE:
1. SA614A data sheets refer to power at 50

input termination; about 21dB less power actually enters the internal 1.5k input.

SA614A (50)

SA614A (1.5k)/SA615 (1.5k)

-97dBm

-118dBm

-47dBm

-68dBm

+3dBm

-18dBm

The SA615 and SA614A are both derived from the same basic die. The SA615 performance plots are directly applicable to the SA614A.

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

INPUT

GND

RSSI

AUDIO

DA
T

GND

OFF

SIGNETICS

NE614 TEST CKT

100nF + 80 20% 63V K1000025V Ceramic

455kHz Ceramic Filter Murata SFG455A3

100nF +10% 50V

455kHz (Ce = 180pF) TOKO RMC 2A6597H

+1% 1/4W Metal Film

150pF +2% 100V N1500 Ceramic

6.8

F +20% 25V Tantalum

1nF +10% 100V K2000-Y5P Ceramic

15nF +10% 50V

100nF +10% 50V

C1
C2
C3

C10

C11

C12

100nF +10% 50V

10pF +2% 100V NPO Ceramic

1500

+1% 1/4W Metal Film

1500

+5% 1/8W Carbon Composition

100k

+1% 1/4W Metal Film

NE614A TEST CIRCUIT

SA614A

INPUT

Q = 20 LOADED

MUTE

INPUT

RSSI

OUTPUT

AUDIO

OUTPUT

DATA

OUTPUT

C10

C12

C11

INPUT

GND

RSSI

AUDIO

DA
T

GND

OFF

SIGNETICS

NE614 TEST CKT

SR00325

Figure 3. SA614A Test Circuit

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

NE604A TEST CIRCUIT

SA604A

MUTE

AUDIO

RSSI

DATA

SA602

+6V

100nF

10nF

47pF

22pF

100nF

5.6pF

44.545
3rd OVERTURE
XTAL

SFG455A3

OUT

CMSG

FILTER

455kHz

Q=20

SFG455A3

+6V

10pF

20

40

60

80

100

10k

100k

120

100

80

60

40

20

AUDIO OUT `C'

MESSAGE

WEIGHTED

614A IF INPUT (

V) (1500

)

(0dB REF = RECOVERED

AUDIO FOR

+8kHz PEAK DEVIA

TION

(dB)

AUDIO

RSSI (VOLTS)

THD + NOISE

AM (80% MOD)

NOISE

602 RF INPUT (dBm) (50

)

0.1

22pF

1nF

0.5

1.3

5.5

6.8

0.21

0.28

100k

0.1

SR00327

Figure 5. Typical Application Cellular Radio (45MHz to 455kHz)

CIRCUIT DESCRIPTION

The SA614A is a very high gain, high frequency device. Correct
operation is not possible if good RF layout and gain stage practices
are not used. The SA614A cannot be evaluated independent of
circuit, components, and board layout. A physical layout which
correlates to the electrical limits is shown in Figure 3. This
configuration can be used as the basis for production layout.

The SA614A is an IF signal processing system suitable for IF
frequencies as high as 21.4MHz. The device consists of two limiting
amplifiers, quadrature detector, direct audio output, muted audio
output, and signal strength indicator (with log output characteristic).
The sub-systems are shown in Figure 4. A typical application with
45MHz input and 455kHz IF is shown in Figure 5.

IF Amplifiers

The IF amplifier section consists of two log-limiting stages. The first
consists of two differential amplifiers with 39dB of gain and a small
signal bandwidth of 41MHz (when driven from a 50

source). The

output of the first limiter is a low impedance emitter follower with
1k

of equivalent series resistance. The second limiting stage

consists of three differential amplifiers with a gain of 62dB and a

small signal AC bandwidth of 28MHz. The outputs of the final
differential stage are buffered to the internal quadrature detector.
One of the outputs is available at Pin 9 to drive an external
quadrature capacitor and L/C quadrature tank.

Both of the limiting amplifier stages are DC biased using feedback.
The buffered output of the final differential amplifier is fed back to the
input through 42k

resistors. As shown in Figure 4, the input

impedance is established for each stage by tapping one of the
feedback resistors 1.6k

from the input. This requires one

additional decoupling capacitor from the tap point to ground.

42k

1.6k

40k

V+

70014

SR00328

Figure 6. First Limiter Bias

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

40k

80k

40k

V+

42k

SR00329

Figure 7. Second Limiter and Quadrature Detector

BPF

SR00330

Figure 8. Feedback Paths

a. Terminating High Impedance Filters with Transformation to Low Impedance

b. Low Impedance Termination and Gain Reduction

BPF

HIGH IMPEDANCE

LOW IMPEDANCE

HIGH IMPEDANCE

BPF

RESISTIVE LOSS INTO BPF

BPF

SR00331

Figure 9. Practical Termination

614A

430

SR00332

Figure 10. Crystal Input Filter with Ceramic Interstage Filter

Because of the very high gain, bandwidth and input impedance of
the limiters, there is a very real potential for instability at IF
frequencies above 455kHz. The basic phenomenon is shown in
Figure 8. Distributed feedback (capacitance, inductance and
radiated fields) forms a divider from the output of the limiters back to
the inputs (including RF input). If this feedback divider does not

cause attenuation greater than the gain of the forward path, then
oscillation or low level regeneration is likely. If regeneration occurs,
two symptoms may be present: (1)The RSSI output will be high with
no signal input (should nominally be 250mV or lower), and (2) the
demodulated output will demonstrate a threshold. Above a certain

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

input level, the limited signal will begin to dominate the regeneration,
and the demodulator will begin to operate in a "normal" manner.

There are three primary ways to deal with regeneration: (1)
Minimize the feedback by gain stage isolation, (2) lower the stage
input impedances, thus increasing the feedback attenuation factor,
and (3) reduce the gain. Gain reduction can effectively be
accomplished by adding attenuation between stages. This can also
lower the input impedance if well planned. Examples of
impedance/gain adjustment are shown in Figure 9. Reduced gain
will result in reduced limiting sensitivity.

A feature of the SA614A IF amplifiers, which is not specified, is low
phase shift. The SA614A is fabricated with a 10GHz process with
very small collector capacitance. It is advantageous in some
applications that the phase shift changes only a few degrees over a
wide range of signal input amplitudes.

Stability Considerations

The high gain and bandwidth of the SA614A in combination with its
very low currents permit circuit implementation with superior
performance. However, stability must be maintained and, to do that,
every possible feedback mechanism must be addressed. These
mechanisms are: 1) Supply lines and ground, 2) stray layout
inductances and capacitances, 3) radiated fields, and 4) phase shift.
As the system IF increases, so must the attention to fields and
strays. However, ground and supply loops cannot be overlooked,
especially at lower frequencies. Even at 455kHz, using the test
layout in Figure 3, instability will occur if the supply line is not
decoupled with two high quality RF capacitors, a 0.1

F monolithic

right at the V

pin, and a 6.8

F tantalum on the supply line. An

electrolytic is not an adequate substitute. At 10.7MHz, a 1

tantalum has proven acceptable with this layout. Every layout must
be evaluated on its own merit, but don't underestimate the
importance of good supply bypass.

At 455kHz, if the layout of Figure 3 or one substantially similar is
used, it is possible to directly connect ceramic filters to the input and
between limiter stages with no special consideration. At frequencies
above 2MHz, some input impedance reduction is usually necessary.
Figure 9 demonstrates a practical means.

As illustrated in Figure 10, 430

external resistors are applied in

parallel to the internal 1.6k

load resistors, thus presenting

approximately 330

to the filters. The input filter is a crystal type for

narrowband selectivity. The filter is terminated with a tank which
transforms to 330

. The interstage filter is a ceramic type which

doesn't contribute to system selectivity, but does suppress wideband
noise and stray signal pickup. In wideband 10.7MHz IFs the input
filter can also be ceramic, directly connected to Pin 16.

In some products it may be impractical to utilize shielding, but this
mechanism may be appropriate to 10.7MHz and 21.4MHz IF. One
of the benefits of low current is lower radiated field strength, but
lower does not mean non-existent. A spectrum analyzer with an
active probe will clearly show IF energy with the probe held in the
proximity of the second limiter output or quadrature coil. No specific
recommendations are provided, but mechanical shielding should be
considered if layout, bypass, and input impedance reduction do not
solve a stubborn instability.

The final stability consideration is phase shift. The phase shift of the
limiters is very low, but there is phase shift contribution from the

quadrature tank and the filters. Most filters demonstrate a large
phase shift across their passband (especially at the edges). If the
quadrature detector is tuned to the edge of the filter passband, the
combined filter and quadrature phase shift can aggravate stability.
This is not usually a problem, but should be kept in mind.

Quadrature Detector

Figure 7 shows an equivalent circuit of the SA614A quadrature
detector. It is a multiplier cell similar to a mixer stage. Instead of
mixing two different frequencies, it mixes two signals of common
frequency but different phase. Internal to the device, a constant
amplitude (limited) signal is differentially applied to the lower port of
the multiplier. The same signal is applied single-ended to an

external capacitor at Pin 9. There is a 90

phase shift across the

plates of this capacitor, with the phase shifted signal applied to the
upper port of the multiplier at Pin 8. A quadrature tank (parallel L/C
network) permits frequency selective phase shifting at the IF
frequency. This quadrature tank must be returned to ground through
a DC blocking capacitor.

The loaded Q of the quadrature tank impacts three fundamental
aspects of the detector: Distortion, maximum modulated peak
deviation, and audio output amplitude. Typical quadrature curves
are illustrated in Figure 12. The phase angle translates to a shift in
the multiplier output voltage.

Thus a small deviation gives a large output with a high Q tank.
However, as the deviation from resonance increases, the
non-linearity of the curve increases (distortion), and, with too much
deviation, the signal will be outside the quadrature region (limiting
the peak deviation which can be demodulated). If the same peak
deviation is applied to a lower Q tank, the deviation will remain in a
region of the curve which is more linear (less distortion), but creates
a smaller phase angle (smaller output amplitude). Thus the Q of the
quadrature tank must be tailored to the design. Basic equations and
an example for determining Q are shown below. This explanation
includes first-order effects only.

Frequency Discriminator Design Equations for
SA614A

VOUT

SR00333

Figure 11.

+ C

1 +

(

)

(1a)

L(C

+ C

)

where

(1b)

= R (C

+ C

)

(1c)

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

From the above equation, the phase shift between nodes 1 and 2, or
the phase across C

will be:

(2)

-1

(

)

Figure 12 is the plot of

vs.

(

)

It is notable that at

, the phase shift is

and the response is close to a straight

line with a slope of

The signal V

would have a phase shift of

with respect to the V

Sin

(3)

If V

= A Sin

= A

t +

Multiplying the two signals in the mixer, and

low pass filtering yields:

Sin

(4)

= A

Sin

t +

after low pass filtering

Cos

(5)

OUT

= 1

Sin

(

)

(6)

OUT

(

)

For

Which is discriminated FM output. (Note that

is the deviation

frequency from the carrier

Ref. Krauss, Raab, Bastian; Solid State Radio Eng.; Wiley, 1980, p.
311. Example: At 455kHz IF, with +5kHz FM deviation. The
maximum normalized frequency will be

455 +5kHz

455

= 1.010 or 0.990

Go to the f vs. normalized frequency curves (Figure 12) and draw a
vertical straight line at

= 1.01.

The curves with Q = 100, Q = 40 are not linear, but Q = 20 and less
shows better linearity for this application. Too small Q decreases

the amplitude of the discriminated FM signal. (Eq. 6)

Choose a

Q = 20

The internal R of the 614A is 40k. From Eq. 1c, and then 1b, it
results that

+ C

= 174pF and L = 0.7mH.

A more exact analysis including the source resistance of the
previous stage shows that there is a series and a parallel resonance
in the phase detector tank. To make the parallel and series
resonances close, and to get maximum attenuation of higher
harmonics at 455kHz IF, we have found that a C

= 10pF and C

164pF (commercial values of 150pF or 180pF may be practical), will
give the best results. A variable inductor which can be adjusted
around 0.7mH should be chosen and optimized for minimum
distortion. (For 10.7MHz, a value of C

= 1pF is recommended.)

Audio Outputs

Two audio outputs are provided. Both are PNP current-to-voltage

converters with 55k

nominal internal loads. The unmuted output

is always active to permit the use of signaling tones in systems such
as cellular radio. The other output can be muted with 70dB typical

attenuation. The two outputs have an internal 180

phase

difference.

The nominal frequency response of the audio outputs is 300kHz.
this response can be increased with the addition of external
resistors from the output pins to ground in parallel with the internal
55k resistors, thus lowering the output time constant. Singe the
output structure is a current-to-voltage converter (current is driven
into the resistance, creating a voltage drop), adding external parallel
resistance also has the effect of lowering the output audio amplitude
and DC level.

This technique of audio bandwidth expansion can be effective in
many applications such as SCA receivers and data transceivers.

Because the two outputs have a 180

phase relationship, FSK

demodulation can be accomplished by applying the two output
differentially across the inputs of an op amp or comparator. Once
the threshold of the reference frequency (or "no-signal" condition)
has been established, the two outputs will shift in opposite directions
(higher or lower output voltage) as the input frequency shifts. The
output of the comparator will be logic output. The choice of op amp
or comparator will depend on the data rate. With high IF frequency
(10MHz and above), and wide IF bandwidth (L/C filters) data rates in
excess of 4Mbaud are possible.

RSSI

The "received signal strength indicator", or RSSI, of the SA614A
demonstrates monotonic logarithmic output over a range of 90dB.
The signal strength output is derived from the summed stage
currents in the limiting amplifiers. It is essentially independent of the
IF frequency. Thus, unfiltered signals at the limiter inputs, spurious
products, or regenerated signals will manifest themselves as RSSI
outputs. An RSSI output of greater than 250mV with no signal (or a
very small signal) applied, is an indication of possible regeneration
or oscillation.

In order to achieve optimum RSSI linearity, there must be a 12dB
insertion loss between the first and second limiting amplifiers. With
a typical 455kHz ceramic filter, there is a nominal 4dB insertion loss
in the filter. An additional 6dB is lost in the interface between the
filter and the input of the second limiter. A small amount of
additional loss must be introduced with a typical ceramic filter. In the
test circuit used for cellular radio applications (Figure 5) the optimum

linearity was achieved with a 5.1k

resistor from the output of the

first limiter (Pin 14) to the input of the interstage filter. With this

resistor from Pin 14 to the filter, sensitivity of 0.25

V for 12dB

SINAD was achieved. With the 3.6k

resistor, sensitivity was

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

optimized at 0.22

V for 12dB SINAD with minor change in the RSSI

linearity.

Any application which requires optimized RSSI linearity, such as
spectrum analyzers, cellular radio, and certain types of telemetry,
will require careful attention to limiter interstage component
selection. This will be especially true with high IF frequencies which
require insertion loss or impedance reduction for stability.

At low frequencies the RSSI makes an excellent logarithmic AC
voltmeter.

For data applications the RSSI is effective as an amplitude shift
keyed (ASK) data slicer. If a comparator is applied to the RSSI and
the threshold set slightly above the no signal level, when an in-band
signal is received the comparator will be sliced. Unlike FSK

demodulation, the maximum data rate is somewhat limited. An
internal capacitor limits the RSSI frequency response to about
100kHz. At high data rates the rise and fall times will not be
symmetrical.

The RSSI output is a current-to-voltage converter similar to the
audio outputs. However, an external resistor is required. With a

91k

resistor, the output characteristic is 0.5V for a 10dB change in

the input amplitude.

Additional Circuitry

Internal to the SA614A are voltage and current regulators which
have been temperature compensated to maintain the performance
of the device over a wide temperature range. These regulators are
not accessible to the user.

200

175

150

125

100

0.95

0.975

1.0

1.025

1.05

Q = 100

Q = 80

Q = 60

Q = 20

Q = 10

SR00334

Figure 12. Phase vs Normalized IF Frequency

) Dw

Philips Semiconductors

Product specification

SA614A

Low power FM IF system

1997 Nov 07

Philips Semiconductors and Philips Electronics North America Corporation reserve the right to make changes, without notice, in the products,
including circuits, standard cells, and/or software, described or contained herein in order to improve design and/or performance. Philips
Semiconductors assumes no responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright,
or mask work right to these products, and makes no representations or warranties that these products are free from patent, copyright, or mask
work right infringement, unless otherwise specified. Applications that are described herein for any of these products are for illustrative purposes
only. Philips Semiconductors makes no representation or warranty that such applications will be suitable for the specified use without further testing
or modification.

LIFE SUPPORT APPLICATIONS
Philips Semiconductors and Philips Electronics North America Corporation Products are not designed for use in life support appliances, devices,
or systems where malfunction of a Philips Semiconductors and Philips Electronics North America Corporation Product can reasonably be expected
to result in a personal injury. Philips Semiconductors and Philips Electronics North America Corporation customers using or selling Philips
Semiconductors and Philips Electronics North America Corporation Products for use in such applications do so at their own risk and agree to fully
indemnify Philips Semiconductors and Philips Electronics North America Corporation for any damages resulting from such improper use or sale.

This data sheet contains preliminary data, and supplementary data will be published at a later date. Philips
Semiconductors reserves the right to make changes at any time without notice in order to improve design
and supply the best possible product.

Philips Semiconductors
811 East Arques Avenue
P.O. Box 3409
Sunnyvale, California 940883409
Telephone 800-234-7381

DEFINITIONS

Data Sheet Identification

Product Status

Definition

Objective Specification

Preliminary Specification

Product Specification

Formative or in Design

Preproduction Product

Full Production

This data sheet contains the design target or goal specifications for product development. Specifications
may change in any manner without notice.

This data sheet contains Final Specifications. Philips Semiconductors reserves the right to make changes
at any time without notice, in order to improve design and supply the best possible product.

Philips

Semiconductors

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: SA614AN

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: SA614AN