Philips SA676DK Datasheet

Philips Semiconductors Product specification

SA676Low-voltage mixer FM IF system

6–129

1993 Dec 15 853-1726 11659

DESCRIPTION

The SA676 is a low-voltage monolithic FM IF system incorporating a
mixer/oscillator, two limiting intermediate frequency amplifiers,
quadrature detector, logarithmic received signal strength indicator
(RSSI), voltage regulator and audio and RSSI op amps. The SA676
is available in a 20-pin SSOP (shrink small outline package).

The SA676 was designed for cordless telephone applications in
which efficient and economic integrated solutions are required and
yet high performance is desirable. Although the product is not
targeted to meet the stringent specifications of high performance
cellular equipment, it will exceed the needs for analog cordless
phones. The minimal amount of external components and absence
of any external adjustments makes for a very economical solution.

FEA TURES

•Low power consumption: 3.5mA typical at 3V

•Mixer input to >100MHz

•Mixer conversion power gain of 17dB at 45MHz

•XTAL oscillator ef fective to 100MHz (L.C. oscillator or external

oscillator can be used at higher frequencies)

•102dB of IF Amp/Limiter gain

•2MHz IF amp/limiter small signal bandwidth

•Temperature compensated logarithmic Received Signal Strength

Indicator (RSSI) with a 70dB dynamic range

•Low external component count; suitable for crystal/ceramic/LC

filters

PIN CONFIGURA TION

RF IN+

RF IN– DECOUPLING

OSC

OUT

OSC

IN

RSSI OUT

7

20 MIXER OUT
19

18 IF AMP IN
17

16 IF AMP OUT
15 GND
14 LIMITER IN

13
12

11 LIMITER OUT

V

CC

DK Package

AUDIO FEEDBACK

8

RSSI FEEDBACK

9

QUADRATURE IN 10

IF AMP DECOUPLING

AUDIO OUT

IF AMP DECOUPLING

LIMITER DECOUPLING

LIMITER DECOUPLING

2

1

3
4

5
6

SR00514

Figure 1. Pin Configuration

•Audio output internal op amp

•RSSI output internal op amp

•Internal op amps with rail-to-rail outputs

•ESD protection: Human Body Model 2kV

Robot Model 200V

APPLICA TION

•Cordless phones

ORDERING INFORMATION

DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG #

20-Pin Plastic Shrink Small Outline Package (Surface-mount) -40 to +85°C SA676DK SOT266-1

BLOCK DIAGRAM

20 19 18 17 16 15 14 13 12 11

10987654321

RSSI

IF
AMP

EB

V

REG

OSCILLATOR

LIMITER

MIXER

QUAD

+–

+–

AUDIO

SR00515

Figure 2. Block Diagram

Philips Semiconductors Product specification

SA676Low-voltage mixer FM IF system

1993 Dec 15

6–130

ABSOLUTE MAXIMUM RATINGS

SYMBOL PARAMETER RATING UNITS

V

CC

Single supply voltage 7 V

T

STG

Storage temperature range –65 to +150 °C

T

A

Operating ambient temperature range –40 to +85 °C

θ

JA

Thermal impedance DK package 117 °C/W

DC ELECTRICAL CHARACTERISTICS

VCC = +3V, TA = 25°C; unless otherwise stated.

LIMITS

SYMBOL PARAMETER TEST CONDITIONS SA676 UNITS

MIN TYP MAX

V

CC

Power supply voltage range 2.7 7.0 V

I

CC

DC current drain 3.5 5.0 mA

AC ELECTRICAL CHARACTERISTICS

TA = 25°C; VCC = +3V , unless otherwise stated. RF frequency = 45MHz; +14.5dBV RF input step-up; IF frequency = 455kHz; R17 = 2.4kΩ
and R18 = 3.3kΩ; RF level = –45dBm; FM modulation = 1kHz with ±5kHz peak deviation. Audio output with de-emphasis filter and C-message
weighted filter. Test circuit Figure 3. The parameters listed below are tested using automatic test equipment to assure consistent electrical
characteristics. 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

MIN TYP MAX

UNITS

Mixer/Osc section (ext LO = 220mV

RMS

)

f

IN

Input signal frequency 100 MHz

f

OSC

Crystal oscillator frequency 100 MHz
Noise figure at 45MHz 7.0 dB
Third–order input intercept point (50Ω

source)

f1 = 45.0; f2 = 45.06MHz
Input RF level = –52dBm

–10 dBm

Conversion power gain Matched 14.5dBV step–up 10 17 dB

50Ω source +2.5 dB
RF input resistance Single–ended input 8 kΩ
RF input capacitance 3.0 4.0 pF
Mixer output resistance (Pin 20) 1.25 1.5 kΩ

IF section

IF amp gain 50Ω source 44 dB
Limiter gain 50Ω source 58 dB
AM rejection 30% AM 1kHz 50 dB
Audio level Gain of two 60 120 mV
SINAD sensitivity IF level –110dBm 17 dB

THD T otal harmonic distortion –55 dB

S/N Signal–to–noise ratio No modulation for noise 60 dB

IF RSSI output, R9 = 2kΩ

1

IF level = –110dBm 0.5 .90 V

IF level = –50dBm 1.7 2.2 V
RSSI range 70 dB
IF input impedance Pin 18 1.3 1.5 kΩ
IF output impedance Pin 16 0.3 kΩ
Limiter input impedance Pin 14 1.3 1.5 kΩ
Limiter output impedance Pin 11 0.3 kΩ
Limiter output voltage Pin 11 130 mV

RMS

Philips Semiconductors Product specification

SA676Low-voltage mixer FM IF system

1993 Dec 15

6–131

AC ELECTRICAL CHARACTERISTICS (Continued)

SYMBOL

PARAMETER TEST CONDITIONS LIMITS UNITS

MIN TYP MAX

RF/IF section (int LO)

System SINAD sensitivity RF level = –114dBm 12 dB

NOTE:

1. The generator source impedance is 50Ω, but the SA676 input impedance at Pin 18 is 1500Ω. As a result, IF level refers to the actual signal
that enters the SA676 input (Pin 18) which is about 21dB less than the “available power” at the generator.

CIRCUIT DESCRIPTION

The SA676 is an IF signal processing system suitable for second IF
systems with input frequency as high as 100MHz. The bandwidth of
the IF amplifier and limiter is at least 2MHz with 90dB of gain. The
gain/bandwidth distribution is optimized for 455kHz, 1.5kΩ source
applications. The overall system is well-suited to battery operation
as well as and high quality products of all types.

The input stage is a Gilbert cell mixer with oscillator. Typical mixer
characteristics include a noise figure of 7.0dB, conversion gain of
17dB, and input third-order intercept of –10dBm. The oscillator will
operate in excess of 100MHz in L/C tank configurations. Hartley or
Colpitts circuits can be used up to 100MHz for xtal configurations.

The output impedance of the mixer is a 1.5kΩ resistor permitting
direct connection to a 455kHz ceramic filter. The input resistance of
the limiting IF amplifiers is also 1.5kΩ. With most 455kHz ceramic
filters and many crystal filters, no impedance matching network is
necessary. The IF amplifier has 44dB of gain and 5.5MHz
bandwidth. The IF limiter has 58dB of gain and 4.5MHz bandwidth.
To achieve optimum linearity of the log signal strength indicator,
there must be a 12dB(v) insertion loss between the first and second
IF stages. If the IF filter or interstage network does not cause
12dB(v) insertion loss, a fixed or variable resistor or an L pad for

simultaneous loss and impedance matching can be added between
the first IF output (Pin 16) and the interstage network. The overall
gain will then be 90dB with 2MHz bandwidth.

The signal from the second limiting amplifier goes to a Gilbert cell
quadrature detector . One port of the Gilbert cell is internally driven
by the IF. The other output of the IF is AC-coupled to a tuned
quadrature network. This signal, which now has a 90° phase
relationship to the internal signal, drives the other port of the
multiplier cell.

The demodulated output of the quadrature drives an internal op
amp. This op amp can be configured as a unity gain buffer, or for
simultaneous gain, filtering, and 2nd-order temperature
compensation if needed. It can drive an AC load as low as 10kΩ
with a rail-to-rail output.

A log signal strength indicator completes the circuitry. The output
range is greater than 70dB and is temperature compensated. This
signal drives an internal op amp. The op amp is capable of
rail-to-rail output. It can be used for gain, filtering, or 2nd-order
temperature compensation of the RSSI, if needed.

NOTE: dB(v) = 20log V

OUT/VIN