Download: RF COMMUNICATIONS PRODUCTS AN1993 High sensitivity applications of low-power RF/IF integrated circuits 1997 Aug 20 Philips Semiconductors

RF COMMUNICATIONS PRODUCTS

AN1993 High sensitivity applications of low-power RF/IF integrated circuits

1997 Aug 20 Philips Semiconductors,

High sensitivity applications of low-power RF/IF

integrated circuits AN1993

ABSTRACT THE BASICS

This paper discusses four high sensitivity receivers and IF First let’s look at why it is relevant to use a 10.7 or 21.4MHz (Intermediate Frequency) strips which utilize intermediate intermediate frequency. 455kHz ceramic filters offer good selectivity frequencies of 10.7MHz or greater. Each circuit utilizes a low-power and small size at a low price. Why use a higher IF? The fundamental VHF mixer and high-performance low-power IF strip. The circuit premise for the answer to this question is that the receiver configurations are architecture is a hetrodyne type as shown in Figure 1. 1. 45 or 49MHz to 10.7MHz narrowband, A pre-selector (bandpass in this case) precedes a mixer and local 2. 90MHz to 21.4MHz narrowband, oscillator. An IF filter follows the mixer. The IF filter is only supposed 3. 100MHz to 10.7MHz wideband, and to pass the difference (or sum) of the local oscillator (LO) frequency 4. 152.2MHz to 10.7MHz narrowband. and the preselector frequency. Each circuit is presented with an explanation of component selection The reality is that there are always two frequencies which can criteria, (to permit adaptation to other frequencies and bandwidths). combine with the LO: The pre-selector frequency and the “image” Optional configurations for local oscillators and data demodulators frequency. Figure 2 shows two hypothetical pre-selection curves. are summarized. Both have 3dB bandwidths of 2MHz. This type of pre-selection is typical of consumer products such as cordless telephone and FM

INTRODUCTION radio. Figure 2A shows the attenuation of a low side image with

Traditionally, the use of 10.7MHz as an intermediate frequency has 10.7MHz. Figure 2B shows the very limited attenuation of the low been an attractive means to accomplish reasonable image rejection side 455kHz image. in VHF/UHF receivers. However, applying significant gain at a high IF has required extensive gain stage isolation to avoid instability and very high current consumption to get adequate amplifier gain

AUDIO

bandwidth. By enlightened application of two relatively new low MXR AND/OR power ICs, Philips Semiconductors SA602 and SA604A, it is DATA possible to build highly producible IF strips and receivers with input frequencies to several hundred megahertz, IF frequencies of 10.7 or 21.4MHz, and sensitivity less than 2µV (in many cases less than PRE SELECT IF FILT IF AMP DEMODFILTER 1µV). The Philips Semiconductors new SA605 combines the

LO

function of the SA602 and the SA604A. All of the circuits described in this paper can also be implemented with the SA605. The SA602 SR00820 andSA604A were utilized for this paper to permit optimum gain Figure 1. Basic Hetrodyne Receiver stage isolation and filter location. PRESELECTOR 10.7MHz IF0 IMAGE 455kHz IF FILTER 0 –10 –10

PRESELECTOR FILTER

–20 –20

DESIRED

–30 LOFREQUENCY –30

LO

–40 –40 IMAGE DESIRED

FREQUENCY

–20 –10 0 +10 +20 ∆ PRESELECTOR FREQ (MHz) –20 –10 0 +10 +20 ∆ PRESELECTOR FREQ (MHz) SR00821 Figure 2. Effects of Preselection on Images 1ST MIXER 2ND MIXER

AUDIO

AND/OR

DATA

PRE SELECT 1ST IF FILTER 2ND IF FILTER IF AMP DEMOD

FILTER

1ST LO 2ND LO SR00822 Figure 3. Dual Conversion 1997 Aug 20 6–2 PRESELECTOR ATTENUATION (dB) PRESELECTOR ATTENUATION (dB),

ZI ZI ZI ZI ZI BPF BPF

SR00823 Figure 4. Feedback Paths 8 VCC 1.5k

BUFFER

6 1.5k 1.5k74520k BIAS BIAS 80k BIAS 10k

GND

SR00824 Figure 5. SA602 Equivalent Circuit If the single conversion architecture of Figure 1 were implemented gain. Higher discrete gain was possible if each stage was carefully with a 455kHz IF, any interfering image would be received almost as shielded and bypassed, but this can become a nightmare on a well as the desired frequency. For this reason, dual conversion, as production line. With so little IF gain available, in order to receive shown in Figure 3, has been popular. signals of less than 10µV it was necessary to add RF gain and this, in turn, meant that the mixer must have good large signal handling In the application of Figure 3, the first IF must be high enough to capability. The RF gain added expense, the high level mixer added permit the pre-selector to reject the images of the first mixer and expense, both added to the potential for instabilities, so the multiple must have a narrow enough bandwidth that the second mixer conversion started looking good again. images and the intermod products due to the first mixer can be attenuated. There’s more to it than that, but those are the basics. But why is instability such a problem in a high gain high IF strip? The multiple conversion hetrodyne works well, but, as Figure 3 There are three basic mechanisms. First, ground and the supply line suggests, compared to Figure 2 it is more complicated. Why, then, are potentially feedback mechanisms from stage-to-stage in any don’t we use the approach of Figure 2? amplifier. Second, output pins and external components create fields which radiate back to inputs. Third, layout capacitances become feedback mechanisms. Figure 4 shows the fields and capacitances

THE PROBLEM symbolically.

Historically there has been a problem: Stability! Commercially available integrated IF amplifiers have been limited to about 60dB of 1997 Aug 20 6–3, 16 15 14 13 12 11 10 9

GND

42k 42k 7k 1.6k 1.6k 40k 40k 35k FULL FULL 2k 2k 8k WAVE WAVE 4.5k RECT. RECT. VOLTAGE/

CURRENT CONVERTER

VEE MUTE QUAD VOLT VOLT REG REG

VCC DET BAND

GAP 40k40k

VOLT VCC

80k 55k 55k 80k 80k GND VCC12345678SR00825 Figure 6. SA604A Equivalent Circuit

MIXER

RF IFT IF AMP IF AMP

IFT AUDIO OUT

S1 QUAD

DETECTOR LO

SR00826 Figure 7. Symbolic Circuit If ZF represents the impedance associated with the circuit feedback The layout capacitance is only part of the issue. In order for mechanisms (stray capacitances, inductances and radiated fields), traditional 10.7MHz IF amplifiers to operate with reasonable gain and ZIN is the equivalent input impedance, a divider is created. This bandwidth, the amount of current in the amplifiers needed to be divider must have an attenuation factor greater than the gain of the quite high. The CA3089 operates with 25mA of typical quiescent amplifier if the amplifier is to remain stable. current. Any currents which are not perfectly differential must be • carefully bypassed to ground. The higher the current, the moreIf gain is increased, the input-to-output isolation factor must be difficult the challenge. And limiter outputs and quadrature increased. components make excellent field generators which add to the • As the frequency of the signal or amplifier bandwidth increases, feedback scenario. The higher the current, the larger the field. the impedance of the layout capacitance decreases thereby reducing the attenuation factor. 1997 Aug 20 6–4, with 3pF. This is not an easy match from 50Ω. In each of the LO INPUT PHILIPS examples which follow, an equivalent 50:1.5k match

NSEA602//60044 DEMO BOARD was used. This compromise of noise, loss, and match yielded good

results. It can be improved upon. Match to crystal filters will require special attention, but will not be given focus in this paper. This oscillator is a single transistor with an internal emitter follower driving the mixer. For best mixer performance, the LO level needs to be approximately 220mVRMS at the base of the oscillator transistor (Pin 6). A number of oscillator configurations are presented at the end of this paper. In each of the prototypes for this paper, the LO source was a signal generator. Thus, a 51Ω resistor was used to terminate the signal generator. The LO is then coupled to the mixer through a DC blocking capacitor. The signal generator is set for

GND

OFF 0dBm. The impedance at the LO input (Pin 6) is approximately M RSSI AUDIO 20kΩ. Thus, required power is very low, but 0dBm across 51Ω doesDATA U provide the necessary 220mVRMS.

T

E The outputs of the SA602 are loaded with 1.5kΩ internal resistors. RF INPUT ON VCC GND GND This makes interface to 455kHz ceramic filters very easy. Other filter types will be addressed in the examples.

THE IF STRIP

The basic functions of the SA604A are ordinary at first glance: Limiting IF, quadrature detector, signal strength meter, and mute switch. However, the performance of each of these blocks is superb. The IF has 100dB of gain and 25MHz bandwidth. This feature will be exploited in the examples. The signal strength indicator has a 90dB log output characteristic with very good linearity. There are two audio outputs with greater than 300kHz bandwidth (one can be muted greater than 70dB). The total supply current is typically 3.5mA. This is the other factor which permits high gain and high IF. Figure 6 shows an equivalent circuit of the SA604A. Each of the IF amplifiers has a 1.6kΩ input impedance. The input impedance is achieved by splitting a DC feedback bias resistor. The input impedance will be manipulated in each of the examples to aid stability. SR00827 BASIC CONSIDERATIONS Figure 8. Circuit Board Layout In each of the circuits presented, a common layout and system methodology is used. The basic circuit is shown symbolically in Figure 7.

THE SOLUTION

The SA602 is a double balanced mixer suitable for input frequencies At the input, a frequency selective transformation from 50Ω to 1.5kΩ in excess of 500MHz. It draws 2.5mA of current. The SA604A is an permits analysis of the circuit with an RF signal generator. A second IF strip with over 100dB of gain and a 25MHz small signal generator provides LO. This generator second generator provides bandwidth. It draws 3.5mA of current. The circuits in this paper will LO. This generator is terminated with a 51Ω resistor. The output of demonstrate ways to take advantage of this low current and 75dB or the mixer and the input of the first limiter are both high impedance more of the SA604A gain in receivers and IF strips that would not be (1.5Ω nominal). As indicated previously, the input impedance of the possible with traditional integrated circuits. No special tricks are limiter must be low enough to attenuate feedback signals. So, the used, only good layout, impedance planning and gain distribution. input impedance of the first limiter is modified with an external resistor. In most of the examples, a 430Ω external resistor was used

THE MIXER to create a 330Ω input impedance (430//1.5kΩ). The first IF filter isthus designed to present 1.5kΩ to the mixer and 330Ω to the first

The SA602 is a low power VHF mixer with built-in oscillator. The limiter. equivalent circuit is shown in Figure 5. The basic attributes of this mixer include conversion gain to frequencies greater than 500MHz, The same basic treatment was used between the first and second a noise figure of 4.6dB @ 45MHz, and a built-in oscillator which can limiters. However, in each of the 10.7MHz examples, this interstage be used up to 200MHz. LO can be injected. filter is not an L/C tank; it is a ceramic filter. This will be explained in the first example. For best performance with any mixer, the interface must be correct. The input impedance of the SA602 is high, typically 3kΩ in parallel 1997 Aug 20 6–5, After the second limiter, a conventional quadrature detector simple low pass filter completes the demodulation process at the demodulates the FM or FSK information from the carrier and a audio outputs. 10.7MHz LO INPUT CERAMIC 0.1µF FILTER 430 51Ω 10.7MHz

CRYSTAL FILTER

10M15A 0.1µF 0.1µF +6V 1pF 1.1µH180pF 10µF 0.1µF876516 15 14 13 12 11 10 9 SA602 0.1µF SA604A1234123456781.5k RF INPUT 47pF 150pF 0.1µF 0.28µH 220pF 430 18pF 15nF 0.1µF 1nF 91k 3.9pF 12µH 56pF

RSSI

MUTE +6V AUDIO DATA SR00828 Figure 9. SA602/604A Demonstration Circuit with RF Input of 45MHz and IF of 10.7MHz ±7.5kHz

CRYSTAL FILTER

0 CERAMIC

FILTER

3– 10.5 10.7 10.9 FREQ|UENCY (MHz) SR00829 Figure 10. Passband Relationship 1997 Aug 20 6–6 RELATIVE FILTER ATTENUATION (dB), 0.7µV 7µV 70µV 0.7mV 7mV 70mV 5.0

AUDIO

0 4.5 -10 4.0 -20 3.5

RSSI

-30 3.0 THD+NOISE -40 2.5 -50 2.0 -60 1.5

NOISE

-70 1.0 -80 0.5 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 RF INPUT (dBm) (50Ω) • 45MHz RF input • 10.7MHz IF • 55.7MHz LO • 15kHz IF BW (odBm) • 7kHz deviation SR00830 Figure 11. VHF or UHF 2nd Conversion (Narrow Band) As mentioned, a single layout was used for each of the examples. shunt path to ground for any stray signal which might feed back to The board artwork is shown in Figure 8. Special attention was given an input; (3) leads were kept short and relatively wide to minimize to: (1) Creating a maximum amount of ground plane with connection the potential for them to radiate or pick up stray signals; finally (and of the component side and solder side ground at locations all over very important), (4) RF bypass was done as close as possible to the board; (2) careful attention was given to keeping a ground ring supply pins and inputs, with a good (10µF) tantalum capacitor around each of the gain stages. The objective was to provide a completing the system bypass. LO INPUT 220pF 0.1µF 430 21.4MHz .33µH CRYSTAL 15pF 0.1µF

FILTER

51Ω 0.1µF 390pF 47pF 0.1µF 0.82pF +6V 0.1µF 0.3µH 10µF 0.1µF 180pF8765.33µH 16 15 14 13 12 11 10 9TANT 270pF 0.1µF SA602 0.1µF SA604A123412345678RF INPUT 56pF 150pF 0.1µF C34 0.06µH 330pF 15nF 0.1µF 1nF 91k

RSSI

MUTE +6V AUDIO DATA SR00831 Figure 12. SA602/604A Demonstration Circuit with RF Input of 90MHz and IF of 21.4MHz ±7.5kHz 1997 Aug 20 6–7 ‘C’ MESSAGE WEIGHTED 0dB REF = RECOVERED AUDIO(VOLTS), 0.7µV 7µV 70µV 0.7mV 7mV 70mV 5.0

AUDIO

0 4.5 -10 4.0 -20 3.5 -30 RSSI 3.0 THD+NOISE -40 2.5 -50 NOISE 2.0 -60 1.5 -70 1.0 -80 0.5 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 RF INPUT (dBm) (50Ω) • 90MHz RF input • 21.4MHz IF • 68.6MHz LO • 15kHz IF BW (odBm) • 7kHz deviation SR00832 Figure 13. UHF Second Conversion (Narrow Band) or VHF Single Conversion (Narrow Band)

EXAMPLE: 45MHZ TO 10.7MHZ NARROWBAND input of the second limiter. Ceramic filters act much like ceramic

As a first example, consider conversion from 45MHz to 10.7MHz. capacitors, so direct connection between two circuit nodes with There are commercially available filters for both frequencies so this different DC levels is acceptable. At the input to the second limiter, is a realistic combination for a second IF in a UHF receiver. This the impedance is again reduced by the addition of a 430Ω external circuit can also be applied to cordless telephone or short range resistor in parallel with the internal 1.6kΩ input load resistor. This communications at 46 or 49MHz. The circuit is shown in Figure 9. presents the 330Ω termination to the ceramic filter which the manufacturers recommend. The 10.7MHz filter chosen is a type commonly available for 25kHz channel spacing. It has a 3dB bandwidth of 15kHz and a termination On the input side of the ceramic filter, no attempt was made to requirement of 3kΩ/2pF. To present 3kΩ to the input side of the filter, create a match. The output impedance of the first limiter is nominally a 1.5kΩ resistor was used between the SA602 output (which has a 1kΩ. Crystal filters are tremendously sensitive to correct match. 1.5kΩ impedance) and the filter. Layout capacitance was close Ceramic filters are relatively forgiving. A review of the enough to 2pF that no adjustment was necessary. This manufacturers’ data shows that the attenuation factor in the series-resistance approach introduces an insertion loss which passband is affected with improper match, but the degree of change degrades the sensitivity, but it has the benefit of simplicity. is small and the passband stays centered. Since the principal selectivity for this application is from the crystal filter at the input of The secondary side of the crystal filter is terminated with a 10.7MHz the first limiter, the interstage ceramic filter only has to suppress tuned tank. The capacitor of the tank is tapped to create a wideband noise. The first filter’s passband is right in the center of transformer with the ratio for 3k:330. With the addition of the 430Ω the ceramic filter passband. (The crystal filter passband is less than resistor in parallel with the SA604A 1.6kΩ internal input resistor, the 10% of the ceramic filter passband). This passband relationship is correct component of resistive termination is presented to the crystal illustrated in Figure 10. filter. The inductor of the tuned load is adjusted off resonance enough to provide the 2pF capacitance needed. (Actual means of After the second limiter, demodulation is accomplished in the adjustment was for best audio during alignment). quadrature detector. Quadrature criteria is not the topic of this paper, but it is noteworthy that the choice of loaded Q will affect If appropriate or necessary for sensitivity, the same type of tuned performance. The SA604A is specified at 455kHz using a termination used for the secondary side of the crystal filter can also quadrature capacitor of 10pF and a tuning capacitor of 180pF. be used between the SA602 and the filter. If this is desired, the (180pF gives a loaded Q of 20 at 455kHz). A careful look at the capacitors should be ratioed for 1.5k:3k. Alignment is more complex quadrature equations (Ref 3.) suggests that at 10.7MHz a value of with tuned termination on both sides of the filter. This approach is about 1pF should be substituted for the 10pF at 455kHz. demonstrated in the fourth example. The performance of this circuit is presented in Figure 11. The –12dB A ceramic filter is used between the first and second limiters. It is SINAD (ratio of Signal to Noise And Distortion) was achieved with a directly connected between the output of the first limiter and the 0.6µV input. 1997 Aug 20 6–8 ‘C’ MESSAGE WEIGHTED 0dB REF = RECOVERED AUDIO (VOLTS), 10.7MHz LO INPUT CERAMIC 0.1µF FILTER 430 0.1µF 51Ω 10.7MHz

CERAMIC FILTER

0.1µF 0.1µF +6V 1pF 1.1µH 10µF 0.1µF 180pF876516 15 14 13 12 11 10 9 SA602 0.1µF SA604A123443012345678RF INPUT 47pF 150pF 0.28µH 220pF 15nF 0.1µF 1nF 91k MUTE +6V RSSI AUDIO DATA SR00833 Figure 14. SA602/604A Demonstration Circuit with RF Input of ~100MHz and IF of 10.7MHz ±140kHz

EXAMPLE: 90MHZ TO 21.4MHZ NARROWBAND but the performance is good nonetheless. The output of the crystal

This second example, like the first, used two frequencies which filter is terminated with a tuned impedance-step-down transformer could represent the intermediate frequencies of a UHF receiver. This as in the previous example. Interstage filtering is accomplished with circuit can also be applied to VHF single conversion receivers if the a 1kΩ:330 step-down ratio. (Remember, the output of the first limiter sensitivity is appropriate. The circuit is shown in Figure 12. is 1kΩ and a 430Ω resistor has been added to make the second limiter input 330Ω). A DC blocking capacitor is needed from the Most of the fundamentals are the same as explained in the first output of the first limiter. The board was not laid out for an interstage example. The 21.4MHz crystal filter has a 1.5kΩ/2pF termination transformer, so an “XACTO” knife was used to make some minor requirement so direct connection to the output of the SA602 is mods. Figure 13 shows the performance. The +12dB SINAD was possible. With strays there is probably more than 2pF in this circuit, with 1.6µV input. 0.7µV 7µV 70µV 0.7mV 7mV 70mV 5.0

AUDIO

0 4.5 -10 4.0 -20 3.5 -30 RSSI 3.0 THD+NOISE -40 2.5 -50 NOISE 2.0 -60 1.5 -70 1.0 -80 0.5 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 RF INPUT (dBm) (50Ω) • 94.7MHz RF input • 10.7MHz IF • 84MHz LO • 280kHz IF BW (odBm) • 75kHz deviation SR00834 Figure 15. FM Broadcast Receiver (Wide Band) 1997 Aug 20 6–9 ‘C’ MESSAGE WEIGHTED 0dB REF = RECOVERED AUDIO (VOLTS), 10.7MHz

CERAMIC

LO INPUT FILTER 430 0.1µF 0.1µF 51Ω 0.1µF 0.1µF +6V 1pF 1.1µH 10µF 0.1µF 180pF876516 15 14 13 12 11 10 9 SA602 0.1µF 10.7MHz SA604A

CERAMIC FILTER

12341234567810M15A RF INPUT 47pF 150pF 0.28µH 220pF 15nF 0.1µF 1nF 91k

RSSI

MUTE +6V AUDIO DATA SR00835 Figure 16. SA602/604A Demonstration Circuit with RF Input of 152.2MHz and IF of 10.7MHz ±7.5kHz the output of the first IF limiter. The secondary sides of both filters 3.50 were terminated with 330Ω as in the two previous examples. While the filter bandpass skew of this simple single conversion receiver VCC = 5.0V might not be tolerable in some applications, to a first order the 3.46 results are excellent. (Please note that sensitivity is measured at +20dB in this wideband example.) Performance is illustrated in 3.42 Figure 15. +20dB SINAD was measured with 1.8µV input. PIN 14 3.38 PIN 12 EXAMPLE: 152.2MHZ TO 10.7MHZ NARROWBAND In this example (see Figure 16) a simple, effective, and relatively 3.34 sensitive single conversion VHF receiver has been implemented. All of the circuit philosophy has been described in previous examples. 3.30 In this circuit, tuned-transformed termination was used on the input -10 0 10 20 30 40 50 60 70 80 AMBIENT TEMPERATURE (°C) and output sides of the crystal filter. Performance is shown in Figure 17. The +12dB SINAD sensitivity was 0.9µV. • 152.2MHz RF input • 10.7MHz IF • 141.5MHz LO • 15kHz IF BW (odBm) • 7kHz deviation OSCILLATORS SR00836 The SA602 contains an oscillator transistor which can be used to Figure 17. VHF Single Conversion (Narrow Band) frequencies greater than 200MHz. Some of the possible configurations are shown in Figures 18 and 19.

EXAMPLE: 100MHZ TO 10.7MHZ WIDEBAND L/C

This example represents three possible applications: (1) low cost, When using a synthesizer, the LO must be externally buffered. sensitive FM broadcast receivers, (2) SCA (Subsidiary Perhaps the simplest approach is an emitter follower with the base Communications Authorization) receivers and (3) data receivers. connected to Pin 7 of the SA602. The use of a dual-gate MOSFET The circuit schematic is shown in Figure 14. While this example has will improve performance because it presents a fairly constant the greatest diversity of application, it is also the simplest. Two capacitance at its gate and because it has very high reverse 10.7MHz ceramic filters were used. The first was directly connected isolation. to the output of the SA602. The second was directly connected to 1997 Aug 20 6–10 OUTPUT BIAS VOLTAGE (V), 4 3 a. Fundamental b. Overtone c. Overtone Colpitts Crystal Colpitts Crystal Butler Crystal 636 3 d. Hartley e. Colpitts L/C Tank L/C Tank SR00837 Figure 18. Oscillator Configurations

CRYSTAL decoding is accomplished by applying a comparator across the

With both of the Colpitts crystal configurations, the load capacitance received signal strength indicator (RSSI). The RSSI will track IF must be specified. In the overtone mode, this can become a level down to below the limits of the demodulator (–120dBm RF sensitive issue since the capacitance from the emitter to ground is input in most of the examples). When an in-band signal is above the actually the equivalent capacitive reactance of the harmonic comparator threshold, the output logic level will change. selection network. The Butler oscillator uses an overtone crystal FSK demodulation takes advantage of the two audio outputs of the specified for series mode operation (no parallel capacitance). It may SA604A. Each is a PNP current source type output with 180° phase require an extra inductor (Lo) to null out Co of the crystal, but relationship. With no signal present, the quad tank tuned for the otherwise is fairly easy to implement (see references). center of the IF passband, and both outputs loaded with the same The oscillator transistor is biased with only 220µA. In order to assure value of capacitance, if a signal is received which is frequency oscillation in some configurations, it may be necessary to increase shifted from the transconductance with an external resistor from the emitter to IF passband, and both outputs loaded with the same value of ground. 10kΩ to 20kΩ are acceptable values. Too small a resistance capacitance, if a signal is received which is frequency shifted from can upset DC bias (see references). the IF center, one output voltage will increase and the other will decrease by a corresponding absolute value. Thus, if a comparator is differentially connected across the two outputs, a frequency shift

DATA DEMODULATION in one direction will drive the comparator output to one supply rail,

It is possible to change any of the examples from an audio receiver and a frequency shift in the opposite direction will cause the to an amplitude shift keyed (ASK) or frequency shift keyed (FSK) comparator output to swing to the opposite rail. Using this technique, receiver or both with the addition of an external op amp(s) or and L/C filtering for a wide IF bandwidth, NRZ data at rates greater comparator(s). A simple example is shown in Figure 20. ASK than 4Mb have been processed with the new SA605. 1997 Aug 20 6–11,

VCC

0.001 MV2105 OR EQUIV 0.8 0.08µH 100k 2k 22k 18k

TO PRESCALER

11pF 0.001 0.001 0.01 V 3SK126 OR EQUIVALENTCC 2pF 6.8µF 100nF 9pF 330Ω876547k 100k 0.01 0.01 10nF SA602123410.7MHz 12pF* K&L 38780 IF OR EQUIV ** 0.01 0.01 2-10pF 0.09µH 2-10pF0.001 11µH 11µH 18k 2-10pF MV2105 OR EQUIV FROM SYNTH LOOP

FILTER

*PERMITS IMPEDANCE MATCH OF NE602 OUTPUT OF 1.8k/8pF TO 3.0k FILTER IMPEDANCE **CHOOSE FOR IMPEDANCE MATCH TO SR00838 Figure 19. Typical Varactor Tuned Application 10.7MHz LO INPUT CERAMIC 0.1µF FILTER 430 0.1µF 51Ω 10.7MHz

CERAMIC FILTER

0.1µF 0.1µF +6V 1pF 3.3µH68pF 10µF 0.1µF876516 15 14 13 12 11 10 9

TANT

0.1µF SA602 0.1µF SA604A123443012345678RF INPUT 0.1µF 91k 100nF FSK OUTPUT

MUTE

+6V ASK OUTPUT SR00839 Figure 20. Basic SA602/604A Data Receiver 1997 Aug 20 6–12,

SUMMARY REFERENCES

The SA602, SA604A and SA605 provide the RF system designer 1) Anderson, D.: “Low Power ICs for RF Data Communications”, with the opportunity for excellent receiver or IF system sensitivity Machine Design , pp 126-128, July 23, 1987. with very simple circuitry. IFs at 455kHz, 10.7MHz and 21.4MHz 2) Krauss, Raab, Bastian: Solid State Radio Engineering , p. 311, with 75 to 90dB gain are possible without special shielding. The Wiley, 1980. flexible configuration of the built-in oscillator of the SA602/605 add to ease of implementation. Either data or audio can be recovered 3) Matthys, R.: “Survey of VHF Crystal Oscillator Circuits,” RF from the SA604A/605 outputs. Technology Expo Proceedings, pp 371-382, February, 1987. 4) Philips Semiconductors: “SA604A High Performance Low Power FM IF System”, Linear Data and Applications Manual, Philips Semiconductors, 1987. 5) Philips Semiconductors; “SA602 Double Balanced Mixer and Oscillator”, Linear Data and Applications Manual, Philips Semiconductors, 1985. 6) Philips Semiconductors: “AN1982–Applying the Oscillator of the SA602 in Low Power Mixer Applications”, Linear Data and Applications Manual, Philips Semiconductors, 1985. 1997 Aug 20 6–13]

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