AN192 A complete FM radio on a chip

INTEGRATED CIRCUITS<strong>AN192</strong>A <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipAuthors: W.H.A. Van Dooremolen and M. Hufschmidt1991 Dec

Philips SemiconductorsApplication noteA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chip<strong>AN192</strong>Authors: W.H.A.Van Dooremolen, M. HufschmidtUntil now, the almost total integration of an <strong>FM</strong> <strong>radio</strong> has beenprevented by the need for LC tuned circuits in the RF, IF, localoscillator and demodulator stages. An obvious way to eliminate thecoils in the IF and demodulator stages is to reduce the normallyused intermediate frequency of 10.7MHz to a frequency that can betuned by active RC filters, the op amps and resistors of which canbe integrated. An IF of zero deems to be ideal because it eliminatesspurious signals such as repeat spots and image response, but itwould not allow the IF signal to be limited prior to demodulation,resulting in poor signal-to-noise ratio and no AM suppression. Withan IF of 70kHz, these problems are overcome and the imagefrequency occurs about halfway between the desired signal and thecenter of the adjacent channel. However, the IF image signal mustbe suppressed and, in common with conventional <strong>FM</strong> <strong>radio</strong>s, thereis also a need to suppress interstation noise and noise when tunedto a weak signal. Spurious responses above and below the centerfrequency of the desired station (side tunings), and harmonicdistortion in the event of very inaccurate tuning must also beeliminated.We have now developed a mono <strong>FM</strong> reception system which issuitable for almost total integration. It uses an active 70kHz IF filterand a unique correlation muting circuit for suppressing spurioussignals such as side responses caused by the flanks of thedemodulator S-curve. With such a low IF, distortion would occur withthe ±75kHz IF swing due to received signals with maximummodulation. The maximum IF swing is therefore compressed to±15kHz by controlling the local oscillator in a frequency-locked loop(FLL). The combined action of the muting circuit and the FLL alsosuppresses image response.The new circuit is the TDA7000 which integrates a mono <strong>FM</strong> <strong>radio</strong>all the way from the aerial input to the audio output. External to theIC are only one tunable LC circuit for the local oscillator, a fewinexpensive ceramic plate capacitors and one resistor. TheTDA7000 dramatically reduces assembly and post-productionalignment costs because only the oscillator circuit needs adjustmentduring manufacture to set the limits of the tuned frequency band.The <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> can be made small enough to fit inside acalculator, cigarette lighter, key-ring fob or even a slim watch. TheTDA7000 can also be used as receiver in equipment such ascordless telephones, CB <strong>radio</strong>s, <strong>radio</strong>-controlled models, pagingsystems, the sound channel of a TV set or other <strong>FM</strong> demodulatingsystems.Using the TDA7000 results in significant improvements for allclasses of <strong>FM</strong> <strong>radio</strong>. For simpler portables, the small size, lack of IFcoils, easy assembly and low power consumption are not the onlyattractive features. The unique correlation muting system and theFLL make it very easy to tune, even when using a tiny tuning knob.For higher-performance portables and clock <strong>radio</strong>s,variable-capacitance diode tuning and station presetting facilities areoften required. These are easily provided with the TDA7000because there are no variable tuned circuits in the RF signal path.Only the local oscillator needs to be tuned, so tracking and distortionproblems are eliminated.The TDA7000 is available in either an 18-lead plastic DIP package(TDA7000), or in a 16-pin SO package (TDA7010T). Futuredevelopments will include reducing the present supply voltage (4.5Vtyp.), and the introduction of <strong>FM</strong> stereo and AM/<strong>FM</strong> versions.Figure 1. A Laboratory Model of the TDA7000 in a Complete <strong>FM</strong> Radio.Also Shown is the TDA7010T in the SO Package Against a CM Scale.SR01154BRIEF DATASYMBOL DESCRIPTION MIN TYP MAX UNITSV CC Typical supply voltage 4.5 VI CC Typical supply current 8 mAf RF RF input frequency range 1.5 110 MHzV RF–3dB Sensitivity for –3dB limiting EMF with Z S = 75Ω, mute disabled 1.5 µVV RF Maximum signal input for THD < 10%, ∆f = ± 75kHz EMF with Z S = 75Ω 200 mVV O Audio output (RMS) with R L = 22kΩ, ∆f = ± 22.5kHz 75 mV1991 Dec2

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>V P(+4.5V)C142.2nFC22C18C17C1547pFC23C12C11220pF330pF100nFL2 (2)39pF150pF3.3nF330pF130nHC10AP2+–18 17 16 15 14 13 12 11 101.4V(1)10kΩAP1+–2.7kΩ10kΩ+IF LIMITERAMPLIFIERIF FILTER4.7kΩ 4.7kΩTDA7000M3M2CORRELATOR<strong>FM</strong> DEMODULATOR13.6kΩAF1AM1+1MUTE2.2kΩ 2.2kΩmute controlIF FILTERVCOV LOOPPFILTERLA2NOISESOURCELOCAL OSC1 2 3 (1)4 5 6 7 8 9V P 56nHL1C7C12C2 C3C4R2C19 27pF3.3nFC5C8150nF22kΩ 1.8nF 22nF10nF10nFC21180pFC2056pFa.f. outputNOTES:1. These pins are not used in the SO package version (TDA7010T) AP = All-Pass filter.2. L 2 is printed on the experimental PCB (Figure 13).L 1 = Toko MC108 No. 514 HNE 150013S13.C 20 = Toko No.2A-15BT-R01.LA1Figure 2. The TDA7000 as a Variable Capacitor-Tuned <strong>FM</strong> Broadcast Receiver700Ω700ΩAF1B12kΩ –SR01155CIRCUIT DESCRIPTIONAs shown in Figure 2, the TDA7000 consists of a local oscillator anda mixer, a two-stage active IF filter followed by an IF limiter/amplifier,a quadrature <strong>FM</strong> demodulator, and an audio muting circuit controlledby an IF waveform correlator. The conversion gain of the mixer,together with the high gain of the IF limiter/amplifier, provides AVCaction and effective suppression of AM signals. The RF input to theTDA7000 for –3dB limiting is 1.5µV. In a conventional portable <strong>radio</strong>,limiting at such a low RF input level would cause instability becausehigher harmonics of the clipped IF signal would be radiated to theaerial. With the low IF used with the TDA7000, the radiation isnegligible.To prevent distortion with the low IF used with the TDA7000, it isnecessary to restrict the IF deviation due to heavily modulated RFsignals to ±15kHz. This is achieved with a frequency-locked loop(FLL) in which the output from the <strong>FM</strong> demodulator shifts the localoscillator frequency in inverse proportion to the IF deviation due tomodulation.Active IF FilterThe first section of the IF filter (AF1A) is a second-order low-passSallen-Key circuit with its cut-off frequency determined by internal2.2kΩ resistors and external capacitors C 7 and C 8 . The secondsection (AF1B) consists of a first-order bandpass filter with the lower1991 Dec 3

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>limit of the passband determined by an internal 4.7kΩ resistor andexternal capacitor C 11 . The upper limit of the passband isdetermined by an internal 4.7kΩ resistor and external capacitor C 10 .The final section of the IF filter consists of a first-order low-passnetwork comprising an internal 12kΩ resistor and external capacitorC 12 . The overall IF filter therefore consists of a fourth-order low-passsection and a first-order high-pass section. Design equations for thefilter are given in Figure 3. Figure 4 shows the measured responsefor the filter.V o /V i(dB)+100–10–20–30–40R12.2kΩ7R12.2kΩ8C8AF1Ag1C7g1 = 0.99R24.7kΩ 10 +C10R2 11 –4.7kΩC11AF1BR312kΩ12C12–50–60–700 100 200 300 400 500f (kHz)Figure 4. Measured Response of the IF FilterSR01157Sallen-Key Filter BP LPSallen-Key circuitgA SK1 j a 2 b1C 7With f Oand Q 0.5 C8A SK2 R 1 C7 C 8g1 jO 1 Q 2 2 OFor C 7 = 3.3nF, C 8 = 180pF; Q = 2.1 and f O = 94kHzBandpass circuitA BPFor f LP1j C 11R 21 j C 10R 2j C 10R 21 j C 11R 21 j C 10R 211and f2 R 2C HP102 R 2C 11f LP1A BP f HPff1 jf HP LP 1 jf 1For C 10 = 330pF, C 11 = 3.3nF, f LP = 103kHz, f HP = 10.3kHzLow-Pass circuit1A LP1 j C 12R 3for f LPA LP 1j LP12 C 12R 3<strong>FM</strong> DemodulatorThe quadrature <strong>FM</strong> demodulator M2 converts the IF variations dueto modulation into an audio frequency voltage. It has a conversiongain of –3.6V/MHz and requires phase quadrature inputs from the IFlimiter/amplifier. As shown in Figure 5, the 90° phase shift isprovided by an active all-pass filter which has about unity gain at allfrequencies but can provide a variable phase shift, dependent on thevalue of external capacitor C 17 .V if– φR1V af+10kΩM2R22.7kΩto correlator17C17With R 2 = 0φ = –2tan –1 ωR 1 C 17for fi 90 o , C 17 1 227pF R 1for f L = 70kHzTo improve the performance of the all-pass filter with theamplitude-limited IF waveform, R 2 has been added.Since this influences the phase angle by 45%, i.e., to 330pFfor f IF = 70kHz.SR01158Figure 5. <strong>FM</strong> Demodulator Phase Shift Circuit (All-Pass Filter)For C 12 = 150pF, f LP = 88.4kHzFigure 3. IF Filter of the TDA7000SR011561991 Dec 4

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>IF Swing Compression With the FLLWith a nominal IF as low as 70kHz, severe harmonic distortion ofthe audio output would occur with an IF deviation of ±75kHz due tofull modulation of a received <strong>FM</strong> broadcast signal. The FLL of theTDA7000 is therefore used to compress the IF swing by using theaudio output from the <strong>FM</strong> demodulator to shift the local oscillatorfrequency in opposition to the IF deviation. The principle is illustratedin Figure 6, which shows how an IF deviation of 75kHz iscompressed to about 15kHz. The THD is thus limited to 0.7% with±22.5kHz modulation, and to 2.3% with ±75kHz modulation.there are two side responses due to the flanks of the demodulatorS-curve. Because the flanks of the S-curve are non-linear, the sideresponses have increased harmonic distortion. In Figure 7, thefrequency and intensity of the side responses are functions of thesignal strength, and they are separated from the correct tuning pointby amplitude minima. However, in practice, the amplitude minimaare not well defined because the modulation frequency and indexare not constant and, moreover, the side response of adjacentchannels often overlap.V af200kHzV rf = 10mVf rfMIXER ANDI.F. AMPLIFIERf ifF.M.DEMODULATOR(CONVERSIONGAIN D =–3.6V/MHz)V afV af1mVfoscC17330pFVOLTAGE–LOOP AMPLIFIER56nHCextCONTROLLEDLOCAL OSC.Cdiode (SLOPE S =–1.14pF/V)A L = –1.06V af 100µVC O = C EXT + C STRAY + C DIODE with open loop = 49pF at f O = 96MHzA LSf OFeedback factor 2 C OOpen-loop conversion gain = D = –3.6V/MHzClosed loop conversion gain D1 D 0.68VMHz for f O 96MHzV af 10µVModulation compression factor k f OSC f RF 1 1K open loop gainclosed loop gain 3.6VMHz0.684VMHz f RF f IF Kfor f RF 75kHz, f 60kHz, f OSC IF 15kHz∆f if = 85 – 70 = 15kHz 5V af 3µVV af1.5µVf OSC = f Of’ OSC f rf∆f OSC = 60kHzf if = 70kHzf’ rf∆f rf = 75kHzf’ rf = 85kHzV af 1µV95.9 95.93 95.99 96 96.075 96.1f rf (kHz)SR01159Figure 6. IF Swing Compression with the FLLV afenlarged invertical direction0.7µVCorrelation Muting System With Open FLLA well-known difference between <strong>FM</strong> and AM is that, for <strong>FM</strong>, eachstation is received in at least three tuning positions. Figure 7 showsthe frequency spectrum of the output from the demodulator of atypical portable <strong>FM</strong> <strong>radio</strong> receiving an RF carrier frequency-modulatedwith a tone of constant frequency and amplitude. In addition to theaudio response at the correct tuning point in the center of Figure 7,SR01160Figure 7. Audio Signal of a Typical Portable Radio as aFunction of Tuned Frequency With RF Input as a Parameter.The Modulation and Amplitude are Both Constant.1991 Dec 5

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>High performance <strong>FM</strong> <strong>radio</strong>s incorporate squelch systems such assignal strength-dependent muting and tuning deviation-dependentmuting to suppress side responses. They also have a tuning meterto facilitate correct tuning. Although the TDA7000 is mainly intendedfor use in portables and clock <strong>radio</strong>s, it incorporates a very effectivenew correlation muting system which suppresses interstation noiseand spurious responses due to detuning to the flanks of thedemodulator S-curve. The muting system is controlled by a circuitwhich determines the correlation between the waveform of the IFsignal and an inverted version of it which is delayed (phase-shifted)by half the period of the nominal IF (180°). A noise generator worksin conjunction with the muting system to give an audible indicationHigh performance <strong>FM</strong> <strong>radio</strong>s incorporate squelch systems such assignal strength-dependent muting and tuning deviation-dependentmuting to suppress side responses. They also have a tuning meterto facilitate correct tuning. Although the TDA7000 is mainly intendedfor use in portables and clock <strong>radio</strong>s, it incorporates a very effectivenew correlation muting system which suppresses interstation noiseand spurious responses due to detuning to the flanks of thedemodulator S-curve. The muting system is controlled by a circuitwhich determines the correlation between the waveform of the IFsignal and an inverted version of it which is delayed (phase-shifted)by half the period of the nominal IF (180°). A noise generator worksin conjunction with the muting system to give an audible indication ofincorrect tuning.Figure 8 illustrates the function of the muting system. Signal IF’ isderived by delaying the IF signal by half the period of the nominal IFand inverting it. With correct tuning as shown in Figure 8a, thewaveforms of the two signals are identical, resulting in largecorrelation. In this situation, the audio signal is not muted. Withdetuning as shown in Figure 8b, signal IF ’ is phase-shifted withrespect to the IF signal. The correlation between the two waveformsis therefore small and the audio output is muted. Figure 8c showsthat, because of the low Q of the IF filter, noise causes considerablefluctuations of the period of the IF signal waveform. There is thensmall correlation between the two waveforms and the audio ismuted. The correlation muting system thus suppresses noise andside responses due to detuning to the flanks of the demodulatorS-curve. Since the mute threshold is much lower than that obtainedwith most other currently-used muting systems, this muting systemis ideal for portable <strong>radio</strong>s which must often receive signals with alevel only slightly above the input noise.largecorrelationwithcorrecttuningI.F.I.F.’(a)As shown in Figure 9, the correlation muting circuit consists ofall-pass filter AP2 connected in series with <strong>FM</strong> demodulator all-passfilter AP1 and adjusted by an external capacitor to provide a totalphase shift of 180°. The output from AP2 is applied to mixer M3which determines the correlation between the undelayed limited IFsignal at one of its inputs and the delayed and inverted version of itat its other input. The output from mixer M3 controls a muting circuitwhich feeds the demodulated audio signal to the output when thecorrelation is high, or feeds the output from a noise source to theoutput to give an audible indication of incorrect tuning when thecorrelation is low. The switching of the muting circuit is progressive(soft muting) to prevent the generation of annoying audio transients.The output from mixer M3 is available externally at Pin 1 and canalso used to drive a detuning indicator.V if<strong>FM</strong>DEMODULATORV ifALL-PASSFILTER(Fig 4)φ 1 =–90°– φR1+ φ 2 =10kΩ–180°18C18 2 2 tan 1 R 1C 18 1for 2 180 o C 18 1 R 1for f if 70kHz,C 18 227pFFigure 9. Correlator of the TDA7000M3mutecontrol1C1SR01162Figure 10 shows that there are two regions where the demodulatedaudio signal is fed to the output because the muting is inactive. Oneregion is centered on the correct tuning point f L . The other iscentered on the image frequency –f L . The image response istherefore not suppressed by the muting system when thefrequency-locked loop is open. When the loop is closed, the timeconstant of the muting system, which is determined by externalcapacitor C 1 , prevents the image response being passed to theaudio output. This is described under the next heading.smallcorrelationdue todetuningI.F.I.F.’(b)very smallcorrelationdue tonoiseI.F.I.F.’(c)SR01161Figure 8. Function of the Correlation Muting System1991 Dec 6

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>Vlock transient A during the short interval while the IF traverses from–f 2 to –f 1 . Since the image response occurs halfway between –f 1and –f 2 , it is also suppressed.<strong>FM</strong> demodulatoroutput voltagelocal oscillatorcontrol voltagecorrelatoroutput voltageONmute functionOFFsidetuningimageresponse0V0V0V0correcttuning(a)f f rf osc(b)f f rf osc(c)f f rf osc(d)f f rf oscFigure 12 shows the audio output from the TDA7000 <strong>radio</strong> as afunction of tuned frequency with aerial signal level as a parameter.Compared with the similar diagram for a typical conventionalportable <strong>radio</strong> (Figure 7), there are three important improvements:1. There are no side responses due to the flanks of the demodulatorS-curve. This is due to the action of the correlation muting system(soft mute) which combines the function of a detuning-dependentmuting system with that of a signal strength-dependent mutingsystem.2. The correct tuning frequency band is wide, even with weak aerialsignals. This is due to the AFC action of the FLL which reduces alarge variation of aerial input frequency (equivalent to detuning) to asmall variation of the IF. There is no audio distortion when the <strong>radio</strong>is slightly detuned.3. Although the soft muting system remains operative with low levelaerial signals, there is no degradation of the audio signal underthese conditions. This is due to the high gain of the IFlimiter/amplifier which provides –3dB limiting of the IF signal with anaerial input level of 1.5µV. However, the soft muting action doesreduce the audio output level with low level aerial signals.audiooutput voltagewith‘soft’ mutingimageside tuningsuppressedcorrecttuning f 1 f 2f 1f 2SR01163f rf f osc(e)∆f OSC≈ ∆ V Of rf f oscFigure 10. Operation of the Correlation Muting System withOpen-Loop FLLCorrelation Muting System With Closed FLLThe closed-loop response of the FLL is shown in Figure 11, in whichthe point of origin is the nominal IF (f RF –f OSC =f L ). With correcttuning, the muting is inactive and the audio signal is fed to theoutput. Spurious responses due to the flanks of the demodulatorS-curve which occur outside the IF band –f 2 to f 2 are suppressedbecause the muting is active. Fast transients of the audio signal dueto locking of the loop (A and B), and to loss of lock (C and D) aresuppressed in two ways.Lock and loss of lock transients B and D occur when the IF isgreater than f 2 and are therefore suppressed because the muting isactive. The situation is different during loss of lock transient Cbecause the muting is only active for the last part of the transient. To<strong>complete</strong>ly suppress this transient, capacitor C 1 in Figure 2 holdsthe muting control line positive (muting active) during the shortinterval while the IF traverses from –f 1 to –f 2 . The same applies forincorrectside tuningsuppressedCAholding rangecapture rangeB= area of correct tuningD∆f rfSR01164Figure 11. Closed-Loop Response of the FLL1991 Dec 7

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>V afV afV afV afV af200kHzV rf = 10mV1mV100µV10µV3µVtuned frequencySL01165Figure 12. Audio Signal of the TDA7000 as a Function of theTuned Frequency with RF Input as a ParameterRECEIVER CIRCUITSCircuits With Variable Capacitor TuningThe circuit diagram of the <strong>complete</strong> mono <strong>FM</strong> <strong>radio</strong> is given inFigure 2. An experimental printed-wiring board layout is given inFigure 13. Special attention has been paid to supply lines and thepositioning of large-signal decoupling capacitors.The functions of the peripheral components of Figure 2 not alreadydescribed are as follows:C 1 – Determines the time constant required to ensure muting ofaudio transients due to the operation of the FLL.C 2 – Together with R 2 determines the time constant for audiode-emphasis (e.g., R 2 C 2 = 40µs.C 3 – The output level from the noise generator during mutingincreases with increasing value of C 3 . If silent mute is required, C 3can be omitted.C 4 – Capacitor for the FLL filter. It eliminates IF harmonics at theoutput of the <strong>FM</strong> demodulator. It also determines the time constantfor locking the FLL and influences the frequency response.C 5 – Supply decoupling capacitor which must be connected as closeas possible to Pin 5 of the TDA7000.C 7 to C 12 , C 17 and C 18 – Filter and demodulator capacitors. Thevalues shown are for an IF of 70kHz. For other intermediatefrequencies, the values of these capacitors must be changed ininverse proportion to the IF change.C 14 – Decouples the reverse RF input. It must be connected to thecommon return via a good quality short connection to ensure alow-impedance path. Inductive or capacitive coupling between C 14and the local oscillator circuit or IF output components must beavoided.C 15 – Decouples the DC feedback for IF limiter/amplifier LA 1 .C 19 and C 21 – Local oscillator tuning capacitors. Their valuesdepend on the required tuning range and on the value of tuningcapacitor C 20 .C 22 , C 23 , L 1 , L 2 – The values given are for an RF bandpass filterwith Q = 4 for the European and USA domestic <strong>FM</strong> broadcast band(87.5MHz to 108MHz). For reception of the Japanese <strong>FM</strong> broadcastband (76MHz to 91MHz), L 1 must be increased to 78nH and L 2must be increased to 150nH. If stopband attenuation for high levelAM or TV signals is not required, L 2 and C 22 can be omitted and C 23changed to 220pF.R 2 – The load for the audio output current source. It determines theaudio output level, but its value must not exceed 22kΩ for V CC =4.5V, or 47kΩ for V CC = 9V.1991 Dec 8

Philips SemiconductorsApplication noteA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chip<strong>AN192</strong>V O(dB)(75mV) 0S + N–20221V rf75Ω220pF220pF1314TDA7000–401NOISETHDTHD(%)105–6010 –6 10 –5 10 –4 10 –3 10 –2 10 –1 1V rf (e.m.f.)0NOTES:The curves numbered 1 were measured with the muting system active. The curves numbered 2 were measured with the muting system disabled by injecting about 20µA intoPin 1 of the TDA7000. The input frequency was 96MHz modulated with 1kHz with a deviation of ±75kHz for the distortion curve.Figure 13. Audio Output as a Function of Input EMFSR01166PERFORMANCE OF THE CIRCUITV CC =4.5V, T A =25°C f RF =96MHz, V RF =0.2mV EMF from a 75Ω source, modulated with ∆f=±22.5kHz, f M =1kHz. Noise voltagemeasured unweighted over the bandwidth 300Hz to 20kHz, unless otherwise specified.SYMBOL PARAMETER TYP MAXEMFEMFEMFEMFSensitivity (EMF voltage)for –3dB limiting:muting disabledfor –3dB mutingfor (S+N)/N=26dBSignal handling (EMF voltage)for THD

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>Circuit With Variable-Capacitance Diode TuningSince it is only necessary to tune the local oscillator coil, it is verysimple to modify the circuit of Figure 2 for variable-capacitancediode tuning. The modifications are shown in Figure 14. A circuitboard layout for the modified receiver and a photograph of a<strong>complete</strong> laboratory model are shown in Figure 15.V P(4.5V)100kΩ82ΩBZX793VO5.6kΩ10nF3.3nFPIN 5BC558V tune100kΩ(log)10kΩ56nHTDA7000(Figure 2)300kΩ1.5kΩBB809PIN 60VPIN 16Figure 14. Variable-Capacitance Diode Tuning for the Local Oscillator.Additional Measures Must be Taken to Ensure Temperature Stability.SR01167100kΩ1.5kΩ300kΩ10nFBZX795.6kΩ10kΩBC55882kΩBB809L13.3nF56nHC8 C7C19C5 C4 C3C109TDA7000110 18L2C12 C22C11 C23 C14C15C17C1C2C18100kΩR2a.f. output+0VL2Figure 15. Circuit Board Layout and Complete Model of a TDA7000 Radio With Variable-Capacitance Diode TuningSL011681991 Dec 10

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>Narrow-Band <strong>FM</strong> ReceiverThe TDA7000 can also be used for reception of narrowband <strong>FM</strong>signals. In this case, the local oscillator is crystal-controlled (asshown in Figure 16) and there is therefore hardly any compressionof the IF swing by the FLL. The deviation of the transmitted carrierfrequency due to modulation must therefore be limited to preventsevere distortion of the demodulated audio signal.The component values in Figure 17 result in an IF of 4.5kHz and anIF bandwidth of 5kHz (Figure 17). If the IF is multiplied by N, thevalues of capacitors C 17 and C 18 in the all-pass filters and thevalues of filter capacitors C 7 , C 8 , C 10 , C 11 , and C 12 must bemultiplied by 1/N. For improved IF selectivity to achieve greateradjacent channel attenuation, second-order networks can be used inplace of C 10 and C 11 .In this circuit the detuning noise generator is not used. Since thecircuit is mainly for reception of audio signals, the audio output mustbe passed through a low-pass Chebyshev filter to suppress IFharmonics.r.f. input+4.5VC183.9nFC174.7nFC154.7µFC23220pFC123.3nFC11100nFC10C144.7nF220pF18 17 16 15 14 13 12 11 10TDA7000(see Fig. 1)9 8 7 6 5 4 3 2 1C1150nFR222kΩC22.7nFC44.7nFC5100nFC7100nFC82.2nFa.f. output200mV RMSSR01169Figure 16. A Narrowband <strong>FM</strong> Receiver With a Crystal-Controlled Local OscillatorV+20i20 logV o +10(dB)0–105kHz3dB25dB–20–30–40–50–600 5 10 15 20f (kHz)SR01170Figure 17. IF Selectivity for the Narrowband <strong>FM</strong> Receiver1991 Dec 11

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>AUDIO AMPLIFIER AND DETUNING INDICATORCIRCUITSAudio output stages suitable for use with the TDA7000 are shown inFigures 18 and 19. Figure 20 shows how the muting signal can beused to operate an LED to give an indication of detuning.+3V220kΩ1nF65Ωearpiecefrom Pin 2TDA70000V1) 1)22kΩ4.7nFBC550BP O = 0.4mW, d = 10%quiescent current = 4mASR01171Figure 18. A 0.4mW Transistor Audio Output Stage WithoutVolume Control for Driving an Earpiece+4.5Vto Pin 5TDA700022Ω220µF+85 3TDA1011APREAMPPOWERAMP42V A+220µFfrom Pin 2TDA70001)1)22kΩ95.6kΩ7100nF614.7Ω8Ω0V4.7nF(log)1.8nF0.1µFNOTE:1. These components replace C2 and R2 in Figure 2. P O = 250mW, d = 10% quiescent current = 8mA.Figure 19. An Integrated 250mW Audio Output StageSR01172+3Vfrom Pin 1of theTDA7000(Fig. 1)0V470kΩBC558SR01173Figure 20. A Detuning Indicator Driven by the Mute SignalFrom the TDA7000ACKNOWLEDGEMENTSThe authors wish to acknowledge the information provided byD. Kasperkovitz and H.v. Rumpt for incorporation in this article.REFERENCENOW, W. and SIEWERT, I., ”Integrated circuitsfor hi-fi <strong>radio</strong>s andtuners’, Electronic Componentsand Applications, Vol. 4, No. 1,November 1981,pp. 11 to 27.1991 Dec 12

Philips SemiconductorsA <strong>complete</strong> <strong>FM</strong> <strong>radio</strong> on a chipApplication note<strong>AN192</strong>NOTES1991 Dec 13