TDA7338 STEREO DECODER INTEGRATED 19KHz SC NOTCH FILTER FOR PILOT CANCELLATION ON CHIP FILTER FOR PILOT DETECTOR AND PLL ADJUSTMENT FREE VOLTAGE CONTROLLED OSCILLATOR AUTOMATIC PILOT DEPENDENT MONO/ STEREO SWITCHING NOISE BLANKING WITH PROGRAMMABLE THRESHOLD HIGH CUT CONTROL AND STEREO BLEND INTEGRATED HIGH PASS FILTER FOR INTERFERENCE DETECTOR LEVEL INPUT FOR ADDITIONAL SPIKE DETECTION ON FIELDSTRENGHT SIGNAL VERY HIGH SUPPRESSION OF HARMONIC AND INTERFERENCE SIGNALS DESCRIPTION The TDA7338 is a new concept of monolithic integrated stereo decoder with noise blanking for FM car radio applications. With the used BICMOS technique, the 19KHz Notch Filter, the PLL Filter and Phase Filter is re- SO20 DIP20 ORDERING NUMBER: TDA7338(DIP20) TDA7338D( SO20) alized on the chip with a Switched Capacitor concept. Avoiding the use of multipliers and non linear circuits a very high performance in terms of noise suppression and total harmonic distortion is reached. PIN CONNECTION (Top view) December 1996 1/11 TDA7338 ABSOLUTE MAXIMUM RATINGS Symbol Parameter V CC DC Supply Voltage ICC Supply Current Tstg Tamb Value Unit 10.5 V 20 mA Storage temperature -55 to 150 °C Operating ambient temperature -40 to 85 °C THERMAL DATA Symbol Description Thermal resistance junction-pins R thj-pins Typ DIP 20 SO 20 Unit 100 200 °C/W ESD All pins are protected against ESD according to the MIL883 standard. BLOCK DIAGRAM AND TEST CIRCUIT 40.2K 1µF MPX PILOT IND. MONO MPX IN 20 1nF 19 VR 18 VSB 17 VHCC 16 1nF HCL 15 HCR 14 13 12 70K IN R 40.2K AMP PILOT DETECTOR 20K LEVEL CONTROL 11 AMP OUT R HIGH CUT CONTROL 80KHz LPF DEMODULATOR 25KHz LPF 19KHz SC NOTCH 20K NOISE BLANKER 10 OUT L AMP 40.2K 9 IN L PLL SC PHASE DETECTOR & PHASE FILTER PEAK DETECTOR AMP DIVIDERS VCO 2 VCO 140KHz LPF 120KHz LPF TRIGGER THRESHOLD 4 REFERENCE CREF 4.7µF 6 1 LEVEL PROG CSB456F11 7 TBLANK 470pF VCO OFF 2/11 PULSE FORMER 8 3 PEAK GND 5 VS 47nF MUTE D95AU364C TDA7338 ELECTRICAL CHARACTERISTICS (VCC = 9V; modulation frequency: 1KHz; de-emphasis time: T = 50µs; nominal MPX input voltage: VMPX = 1.5VPP; m 100% (75KHz deviation, fmod = 1KHz); RIN = 40.2kΩ, ROUT = 40.2kΩ; Tamb = 27°C; CREF = 4.7µF; unless otherwise specified) Symbol VCC ICC Parameter Supply Voltage Supply Current Test Condition Min. 7.5 5 VIN VORMS MPX Input Level (peak to peak) A.F. Output Voltage (mono) SVRR VL/VR Supply Voltage Ripple Rejection Difference of Output Voltage Levels fm = 1KHz pin 10 and 11VIN = 0.5VRMS MONO; VRIPPLE = 200mV; f = 1KHz pin 10 and 11- mono Vo/Vi RO VO Gain Output Resistance DC Output Voltage V10/V20 pin 10 and 11 pin 10 and 11 4.2 α THD S+N N Channel Separation Total Harmonic distortion Signal plus noise to noise ratio VR - VSB = -50mVDC 30 αM VDC Muting Attenuation Mute DC Steps at pins 10, 11 Typ. 9 10 Max. 10.2 15 1.5 1.5 V V 40 -0.8 55 8.5 9.5 10 4.5 10.5 50 4.8 45 0.02 91 0.3 f = 20Hz to 16KHz; S = 2Vrms V7 and V8 < 0.6V Mute at pin 8 0.8 100 0 Unit V mA 4 dB dB dB Ω V dB % dB dB mV CARRIER AND HARMONIC SUPPRESSION AT THE OUTPUT α19 α38 α57 α76 Pilot Signal f = 19KHz Subcarrier f = 38KHz Subcarrier f = 57KHz 55 Subcarrier f = 76KHz 70 75 62 dB dB dB 90 dB INTERMODULATION (note 1) α2 fmod = 10KHz; fspur = 1KHz 65 dB α3 fmod = 13KHz; fspur = 1KHz 75 dB 70 dB 75 dB TRAFFIC RADIO (note 2) α57 Signal f = 57KHz SCA - SUBSIDIARY COMMUNICATIONS AUTHORIZATION (note 3) α67 Signal f = 67KHz ACI - ADJACENT CHANNEL INTERFERENCE (note4) α114 Signal f = 114KHz 95 dB α190 Signal f = 190KHz 84 dB MONO/ STEREO SWITCH VINTH Pilot Threshold Voltage for stereo ”ON” 12 20 28 mVRMS VINTH VPI IPI Pilot Threshold Voltage Pilot Indicator Saturation Voltage Pilot Indicator Leakage Current for stereo ”OFF” I = 1mA V = 9V 7 14 0.2 21 0.5 10 mVRMS V V 19 Control Voltage for forced mono α = < 3dB 0.8 µA V -0.23 V -30 mV STEREO BLEND V16-17 V16-17 Control Voltage for Channel Separation Control Voltage for Channel Separation α = 6dB; VR = 3.6V (note 5) α = 26dB; -0.31 -85 -0.27 -55 3/11 TDA7338 ELECTRICAL CHARACTERISTICS (continued) HIGH CUT CONTROL Symbol Test Condition Min. Typ. Max. Unit τdeemp De-Emphasis Time Constant Parameter C 13, C14 = 1nF; V15-17 = 50mV 43 50 57 µs R15 -17 High Cut Control Resistance V15 - 17 = 50mV 43 50 57 KΩ R15 -17 High Cut Control Resistance V15 - 17 = -0.5V (note 5) 115 150 185 KΩ fosc Oscillator Frequency with Murata CSB456F11 ∆f/f Capture and Holding Range VCO VVCO VCO OFF 456 KHz ±1 Pin 7 % 0.6 V NOISE INTERFACE DETECTOR (test condition: VSB > VR + 50mV) V TR V TR Trigger Threshold (note 6) Trigger Threshold TS Suppression Pulse Duration IOS Input Offset Current during suppression time VPEAK = 1.3V; PROG = GND 180 mV VPEAK = 1.3V; PROG = OPEN/VDD 250 mV VPEAK = 1.5V; PROG = GND 260 mV VPEAK = 1.5V; PROG = OPEN/VDD 340 mV C BLANK = 470pF 50 µs 10 pA V N1 VPEAK (pin 8) VIN = 0mVRMS 0.7 1.0 1.3 V N2 VPEAK (pin 8) VIN = 50mVRMS; f = 150KHz 1.1 1.5 2 V V N3 VPEAK (pin 8) VIN = 100mVRMS; f = 150KHz 1.7 2.3 2.8 V NOTES TO THE CHARACTERISTICS 1 INTERMODULATION SUPPRESSION α2 = VO (signal) (at1KHz) ; fs = (2 x 10KHz) - 19KHz VO (spurious) (at1KHZ) α3 = VO (signal) (at1KHz) ; fs = (3 x 13KHz) - 38KHz VO (spurious) (at1KHZ) measured with : 91% mono signal; 9% pilot signal; fm=10KHz or 13KHz 2. TRAFFIC RADIO (V.F.) suppression α57 (V.W.F.) = VO(signal) (at1KHz) VO (spurious) (at1KHZ ±23Hz) measured with : 91% stereo signal; 9% pilot signal; fm=1KHz; 5% subcarrier (f=57KHz, fm = 23Hz AM, m = 60%) 3. SCA (SUBSIDIARY COMMUNICATIONS AUTHORIZATION) α67 = VO(signal) (at1KHz) ; fs = (2 x 38KHz) - 67KHz VO (spurious) (at9KHZ) measured with : 81% mono signal; 9% pilot signal; fm=1KHz; 10% SCA - subcarrier (fs = 67KHz, unmodulated) 4/11 V TDA7338 NOTES TO THE CHZARACTERISTICS (continued) 4. ACI (ADJACENT CHANNEL INTERFERENCE) α114 = VO (signal) (at1KHz) ; fs = 110KHz - (3 x 38KHz) VO (spurious) (at4KHZ) α190 = VO (signal) (at1KHz) ; fs = 186KHz - (5 x 38KHz) VO (spurious) (at4KHZ) measured with : 90% mono signal; 9% pilot signal; fm=1KHz; 1% spurious signal (fs = 110KHz or 186KHz, unmodulated) 5. Control range typ 11% of VR (see figure 1 and figure2) 6. MEASUREMENT OF TRIGGER THRESHOLDS All thresholds are measured by using a pulse with TR = 2µs, THIGH = 2µs, and TF = 10µs. The repetition rate must not increase the PEAK voltage. Vin V TR DC D95AU365 TR THIGH Time TF FUNCTIONAL DESCRIPTION Signal Path The TDA7338 Stereodecoder contains all necessary functions for processing the MPX signal. Due to the external input resistance (Pin 20) the circuit can be adapted to different MPX input levels. Behind a 80kHz lowpass filter the adjustment free PLL for the pilot Tone is placed. The only external component needed for the PLL is the ceramic resonator for the oscillator which runs at 456kHz. The pilot detector output is designed as an open collector output, therefore an external pullup resistor is needed. To force the decoder to ”MONO” Pin 19 has to be clamped to a voltage below 0.8V. The voltage level (signal strength from the IF part) applied to Pin 15 (VHCC) allows to control the time constant of the deemphasis (nom. = 50µs, see fig. 1). If the RF-signal is weak, the corner Figure 1: High Cut Control Figure 2: Stereo Blend D95AU366 fc (KHz) D95AU367 SEP (dB) 50 3.18 (=50µs) 40 VR=3.6V V R=3.6V 30 2 20 1 10 0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 VHCC-VR(V) 0 -0.40 -0.32 -0.24 -0.16 -0.08 VSB-VR(V) 5/11 TDA7338 frequency is reduced down to 1kHz to improve the signal to noise ratio. Furthermore the conditions of the stereo separation (see fig.2) can be controlled through the signal applied to Pin 16 (VSB). Both signal levels (VSB and VHCC) are referred to Pin 17 (VR), with the characteristic that the control range is 11% of VR. By modifying the feedback resistor value of the output stages (Pin 9 - 10, Pin 11 - 12) the total gain of the stereodecoder can be modified. Pin 7 and Pin 8 have an additional function. By pulling them to ground the VCO-OFF (Pin 7) and the MUTE (Pin 8) function are activated. The MUTE signal disconnects the MPX-signal from the circuit, while in combination with VCO-OFF also the output buffers are disconnected from the circuit. In this mode the output buffers can be used for AM-stereo, cassette play back and other purposes. AM Mono Mode By selecting VCO-OFF (Pin 7 to GND) the VCO is switched off and the SB and HCC are disabled. The deemphasis time constant is changed to 40µs (fc = 4KHz). DESCRIPTION OF THE NOISE BLANKER In the normal automotive environment the MPX signal is disturbed by ignition spikes, motors and high frequency switches etc. The aim of the noise blanker part is to cancel the influence of the spikes produced by these components. Therefore the output of the stereodecoder is switched off for a time of 40µs (average spike duration). In a first stage the spikes must be detected but to avoid a wrong triggering on high frequency noise a complex trigger control is implemented. Behind the trigger stage a pulse former generates the 40µs ”blanking” pulse. This duration of 40µs can be varied by changing the capacitor at pin 7. 1.1 Trigger Path The incoming MPX signal is highpass-filtered, amplified and rectified (block RECT-PEAK). The second order highpass-filter has a corner-frequency of 140KHz. The rectifier signal, RECT, is used to generate by peak-rectification a signal called PEAK, which is available at the PEAK pin 8. Also noise with a frequency >100KHz increases the PEAK voltage. The value of the PEAK voltage influences the trigger threshold voltage Vth (block ATC). The higher the noise level the higher the threshold. Both signals, RECT and PEAK+Vth are fed to a comparator (block PEAK-COMP) which outputs a 6/11 sawtooth-shaped waveform at the TBLANK pin 7. A second comparator (block BLANK-COMP) forms the internal blanking duration of 40µs. The noise blanker is supplied by his own biasing circuit (block BIAS-MONO) to avoid any cross talk to the signal path (block BIAS-MONO). 1.2 Noise Controlled Threshold Adjustment (ATC) The behaviour of the noise controlled threshold adjustment is shown in fig. 4. It can be influenced slightly by adding a resistor in parallel to the PEAK capacitor at Pin 8 either to GND or VDD. A resistor to GND will decrease the threshold whereas a resistor to VDD will increase it. But it is recommended to choose one of the internal thresholds by use of the PROG pin (see table 1) 1.3 Automatic Threshold Control by the Stereoblend voltage (ATC-SB) Besides the noise controlled threshold adjustment there is an additional possibility for influencing the trigger. It is controlled by the difference between Vsb and Vr, similar to the Stereoblend. The reason for implementing such a second control will be explained in the following: The point where the MPX signal starts to become noisy is fixed by the RF part. Therefore also the starting point of the normal noise controlled trigger adjustment is fixed (fig.5). But in some cases the behaviour of the noiseblanker can be improved by increasing the threshold even in a region of higher fieldstrength, for the MPX signal often shows distortion in this range, which leads to an undesired triggering. Because of the overlap of this range and the range of the stereo/mono transition it can be controlled by Vsb and Vr. This threshold increase is programmable(see fig. 5). 1.4 Blend Mode Another possibility to avoid a disturbing triggering on modulation is to use the spikes on the fieldstrength signal (LEVEL pin). But in the range of higher fieldstrength the signal saturates and no more spike detection is possible. For this reason the TDA7338 offers the ”BLEND MODE”. When ”BLEND MODE” is activated a smooth transition between the LEVEL- and the MPX-signal is used to detect the spikes either on LEVEL or on MPX. In the lower fieldstrength range mainly the LEVEL-signal is used whereas in the higher range mainly the MPX is used. This switching is controlled also by the normal Stereoblend signal to avoid additional pins. ”BLEND MODE OFF” is activated by connecting the LEVEL pin to GND (LEVEL must be also connected to GND if not used). TDA7338 Figure 3: Block Diagram of the Noise Blanker LEFT 80KHz LP SIGNAL PATH BLANK COMP PEAK COMP REF. + + RECT 140KHz HP MPX IN AMP PEAK BUF AUTOMATIC THRESHOLD CONTROL ATC 120KHz HP LEVEL to OUTPUTS RIGHT PEAK+VTH 40µs 2V VS THRESHOLD L/H RECT-PEAK PROG BLEND CONTROL BLEND ON/OFF 0.1V ADDITIONAL THRESHOLD CONTROL on/off + - ADDITIONAL THRESHOLD CONTROL (ATC-SB) 7V VR VSB CPEAK 47nF CBLANK 330pF D95AU368 Table 1: Programming of the Noiseblanker PIN 1 (PROG) Trigger Threshold Peak Voltage Control By Fieldstrength ON GND LOW OPEN HIGH ON VDD HIGH OFF Figure 4: Trigger Threshold vs. VPEAK VTH 300mV 180mV MIN. TRIG. THRESHOLD NOISE ADJUSTED TRIG. THRESHOLD 100mV 60mV 0.9V D95AU369 1.5V VPEAK(V) 7/11 TDA7338 Figure 5: Behaviour of the Field Strength Controlled Threshold Adiustment VPEAK MONO STEREO ≈3V 2.2V TRIG. THRESHOLD 0.9V NOISE ATC_SB OFF (PROG=VS) noisy signal good signal D95AU370 E’ Figure 6: Application Diagram 1nF 2) 68K 1) SIGNAL STRENGTH 15 14 47K 13 47K 1) 16 1nF 2) 47K VR 12 17 PILOT_IND 18 19 TDA7338 100K MONO 68K 470nF IN R 47K 11 OUT 6 LEVEL (SIGNAL STRENGTH) 9 IN L 47K 33K 56pF 3) 56pF 3) 10K 20 MPX 10 OUT 4) 1 100K VCO_OFF (FM ENABLE) 7 8 680pF 2 4 5 3 10K MUTE 100K 330pF 456KHz 10µF 100nF 47nF 10K D95AU371A VS 9V 1) 2) 3) 4) 8/11 has to be adapted to the signal strength for deemphasis = 50µs not absolutely necessary roll off: to be adjusted to the tuner part TDA7338 SO20 PACKAGE MECHANICAL DATA mm DIM. MIN. TYP. A a1 inch MAX. MIN. TYP. 2.65 0.1 0.104 0.3 a2 MAX. 0.004 0.012 2.45 0.096 b 0.35 0.49 0.014 0.019 b1 0.23 0.32 0.009 0.013 C 0.5 0.020 c1 45 (typ.) D 12.6 13.0 0.496 0.512 E 10 10.65 0.394 0.419 e 1.27 0.050 e3 11.43 0.450 F 7.4 7.6 0.291 0.299 L 0.5 1.27 0.020 0.050 M S 0.75 0.030 8 (max.) 9/11 TDA7338 DIP20 PACKAGE MECHANICAL DATA mm DIM. MIN. a1 0.254 B 1.39 TYP. MAX. MIN. TYP. MAX. 0.010 1.65 0.055 0.065 b 0.45 0.018 b1 0.25 0.010 D 25.4 1.000 E 8.5 0.335 e 2.54 0.100 e3 22.86 0.900 F 7.1 0.280 I 3.93 0.155 L Z 10/11 inch 3.3 0.130 1.34 0.053 TDA7338 Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGSTHOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics. 1996 SGS-THOMSON Microelectronics – Printed in Italy – All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. 11/11