U2514B

U2514B AM/FM Receiver for Digital Tuning with FM-Stereo Decoder Description The U2514B is an integrated bipolar radio suitable for digital tuning systems. It contains a FM front end with pre-amplifier and FM-stereo decoder as well as a complete AM receiver and demodulator. Stop-signal generation is implemented for FM and AM mode. This circuit is designed for use in small radios, power packs and multimedia applications Features D FM wideband AGC D LO-buffer for digital tuning D Integrated stop signal generation with true AM/ FM discriminators D High cut D Mute function D Pilot canceller D Supply voltage range 3 to 12 V D Package: SSO28 D Adjustable stop signal sensitivity D Automatic stereo-mono-blend Block Diagram FMOSCE FMOSCB FMRF 6 28 FMIN 2 FMAGC 8 OSCOUT GNDRF 4 AM FM stop signal detect 20 Pilot PLL 23 CTRLB 27 1 AMIN AM front end AM IF + demodulator Control unit VS V Ref GND 16 7 AMOSC IFOUT 10 12 FMIFIN AMIFIN 13 17 METER 9 22 26 AMFM 14 VREF 12305 AFSM FMDET 15 11 MPXOUT 25 MPXIN 24 Matrix decoder + HCC 18 OUTR 19 OUTL 21 LPF 5 3 FM front end FM IF + demodulator CERES CTRLA AMSADJ Figure 1. TELEFUNKEN Semiconductors Rev. A2, 04-Nov-96 1 (15) Preliminary Information U2514B Pin Description Pin 1 2 3 4 5 6 7 8 9 FMOSCB 6 AMOSC 7 OSCOUT 8 AMSADJ 9 IFOUT 10 AFSM 11 23 CTRLB 22 CTRLA 21 LPF 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Function AM antenna input FM-AGC time constant FM RF tank Ground RF FM oscillator emitter FM oscillator basis AM oscillator Buffered AM/FM oscillator output AMSADJ Current-input for AM stop signal adjust IFOUT AM/FM IF output AFSM AF smoothing voltage FMIFIN FM IF amplifier input AMIFIN AM IF amplifier input VREF Reference voltage FMDET FM discriminator output GND Ground METER Fieldstrength voltage output OUTR AF output right OUTL AF output left CERES Resonator 456 kHz LPF Low pass filter for Pilot-PLL CTRLA Control input for mute, search mode and search sensitivity CTRLB Control input for forced mono, control output for stop function and stereo information MPXIN Stereo decoder MPX input MPXOUT AM/FM MPX output AMFM AM/FM switch and pilot canceller time constant VS Supply voltage FMIN FM antenna input Symbol AMIN FMAGC FMRF GNDRF FMOSCE FMOSCB AMOSC OSCOUT AMIN 1 FMAGC 2 FMRF GNDRF FMOSCE 3 4 5 28 FMIN 27 VS 26 AMFM 25 MPXOUT 24 MPXIN 20 CERES 19 18 17 16 15 10547 OUTL OUTR METER GND FMDET FMIFIN 12 AMIFIN 13 VREF 14 24 25 26 27 28 Figure 2. Pinning Ordering and Package Information Extended Type Number U2514B-AFN U2514B-AFNG3 Package SSO28 SSO28 Remarks Taping according to ICE-286-3 2 (15) Preliminary Information TELEFUNKEN Semiconductors Rev. A2, 04-Nov-96 U2514B Pin Description FMIN, FMAGC, FMRF FMOSCE, FMOSCB FMOSCB 3 VREF FMRF MIXER 6 FMOSCE 5 FMAGC 1.2 k FMON T1 T2 2 I AGC GNDRF Figure 4. 12415 FMIN 28 1.5 k FMON GNDRF 12414 Figure 3. The FM local oscillator consists of a transistor in grounded collector configuration. The negative resistance at the base of the transistor is generated by an external capacitor connected between emitter FMOSCE (Pin 5) and GNDRF (Pin 4) An other external capacitor is connected between base FMOSCB (Pin 6) and emitter FMOSCE (Pin 5) which increases the resistance at the emitter and leads to a higher oscillator swing. The negative resistance at FMOSCB is approximately 250 W. Therefore, the resonant LO tank resistance of approximately 5 kW (depends on Q-factor of the coil) is transformed to this magnitude via a capacitor. OSCOUT 8 The FM pre-amplifier input FMIN (Pin 28) consists of a transistor grounded base circuit (T2) which provides excellent noise performance and large signal behavior. It is recommended to connect a source impedance of 100 W in order to achieve optimal performance. The dc current through the amplifying transitor is reduced by the internal AGC. This means in the case of large input signals, the input ac current is bypassed via the wideband AGC transistor T1. A capacitor is connected between FMAGC (Pin 2) and GNDRF (Pin 4). It shortens the transistor base to GNDRF and it also serves for smoothing of the AGC voltage. A tuned RF circuit is connected between FMRF (Pin 3) and VS (Pin 27). The amplified RF signal is fed internally to the mixer input. OSCOUT FM AM 12416 Figure 5. A resistor is connected between OSCOUT (Pin 8) and VREF (Pin 14). It determines the amplitude of oscillator voltage which is fed to the PLL circuit. The TEMIC PLL familiy U428xBM is recommended because it offers high signal to noise ratio and low current consumption. TELEFUNKEN Semiconductors Rev. A2, 04-Nov-96 3 (15) Preliminary Information U2514B AMIN VREF AMSADJ 12418 9 AMSADJ AMIN 1 GND I AGC GNDRF Figure 6. Figure 8. 12417 The AM antenna coil is connected between AMIN (Pin 1) and VREF (Pin 14). In order to ensure that the AGC operates correctly, a coil impedance of approximately 25 kW is necessary. AMOSC 7 AMOSC The ceramic resonator of the stereo decoder PLL circuit is used as a stop signal detector for AM signals. For this purpose, the parallel resonance frequency of the resonator, which is unloaded about 456 kHz, is reduced by an internal load capacitor down to 455 kHz. Therefore, the AM IF must be 455 kHz. The internal loading capacitor is defined by the current through AMSADJ (Pin 9) to GND. An external resistor is connected between AMSADJ (Pin 9) and GND. It allows the alignment of the stop signal center frequency. The width of the stop window is typicaly 800 Hz. If AM searchmode is not activated, the pin is internally pulled to ground. VREF IFOUT 6k AMON FM 12419 10 IFOUT AM GNDRF Figure 7. Figure 9. 12420 The AM oscillator has to be loaded by an external tank referred to VREF (Pin 14). If reduction of the oscillator voltage is necessary, this may be achieved by a parallel resistor. The IF output (IFOUT Pin 10) of both the FM and the AM mixer has to be loaded into external IF-tank circuits refered to VREF (Pin 14). Q-factor of IF coils must not be lower than 50. 4 (15) Preliminary Information TELEFUNKEN Semiconductors Rev. A2, 04-Nov-96 U2514B AMIFIN FMDET VREF VREF 3.3 k 13 AMIFIN 12421 15 FMDET 150 mA 12422 Figure 10. Figure 12. The input impedance of the AM IF amplifier is 3.3 kW according to the required impedance of most ceramic filters. The input refers to VREF (Pin 14). The discriminator allows the connection of a ceramic resonator or LC tank. A minimization of THD and adjustment of center frequency versus temperature can only be achieved by using a LC tank. This performs a temperature independent stop signal. FMIFIN AFSM 25 40 mA 100 k 12 MPXOUT 11 AFSM FMIFIN 12423 GND Figure 13. Figure 11. 12424 The input impedance of the FM IF amplifier is 330 W according to the required impedance of most FM ceramic filters. The input referes to GND (Pin 16). A capacitor is connected between AFSM (Pin 11) and GND for smoothing of the FM-AF. This is necessary to generate a modulation independent stop signal. (Because the deviation of the FM signal (75 kHz) can be greater than the stop signal window (25 kHz)). In the AM-search-mode, the external capacitor smoothes the demodulated AM-IF-signal. TELEFUNKEN Semiconductors Rev. A2, 04-Nov-96 5 (15) Preliminary Information U2514B METER VREF 12425 CTRLB VS 30 k 23 1.2 V CTRLB FM AM 12447 17 METER GND Figure 16. Figure 14. This pin is driven by a current corresponding to the level of the FM or AM-IF-signal. The required external load consists of a resistor (100 to 150 kW) in parallel with an external capacitor (e.g., 10 mF necessary to achieve a good THD in AM mode and to supress AF influence in FM mode). The voltage at this pin controls the high cut and mono/ stereo blend function in the case of reception mode. These functions can be affected by the designer by choosing different values of the load resistor. The signal at the output CTRLB (Pin 23) shows stereo or mono reception. The stereo reception is indicated if the voltage is higher than 1.2 V, otherwise it is mono. Furthermore there is the possibility to force the receiver circuit to mono by applying an external control voltage