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features ? high dynamic range for am and fm integrated agc for fm high intercept point 3rd-order for fm fm amplifier adjustable to various cable impedances high intercept point 2nd-order for am low-noise output voltage low power consumption electrostatic sensitive device. observe precautions for handling. 1. description the atr4254 is an integrated low-noise am/fm antenna impedance matching circuit in bicmos technology. the device is design ed specifically for car applications and is suitable for windshield and roof antennas. figure 1-1. block diagram fm agc fmin agc vs amin amout vref1 fmout fmgain gnd1 i agc agcadj gnd2 vref2 vref 1 (14) 2 (15) 4 (2) 3 (16) 5 (3) 7 (5) 8 (6) 10 (7) 14 (11) 12 (9) 13 (10) 15 (13) amout1 11 (8) am () pin numbers in brackets = qfn16 4 4 package low-noise am/fm antenna impedance matching ic atr4254 rev. 4879a?audr?09/05
2 4879a?audr?09/05 atr4254 2. pin configuration figure 2-1. pinning so16 figure 2-2. pinning qfn16 4 4 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 fmgain agc vref2 nc gnd2 amin fmin gnd1 vs agcadj vref1 amout1 amout nc nc fmout nc agc vref2 nc nc vs agcadj vref1 fmgain fmgnd fmin fmout gnd2 amin amout amout1 16 15 14 13 5 6 7 8 1 2 3 4 12 11 10 9 table 2-1. pin description pin sso16 pin qfn16 symbol function 1 14 fmin fm input 2 15 gnd1 ground for fm part 3 16 fmgain fm gain adjustment 42agcagc output 5 3 vref2 reference voltage 2 output 6 1 nc not connected 7 5 gnd2 ground for am part 8 6 amin am input 9 4 nc not connected 10 7 amout am output 11 8 amout1 am output 12 9 vref1 reference voltage 1 output 13 10 agcadj adjustment fm wide-band agc threshold 14 11 vs supply voltage 15 13 fmout fm output 16 12 nc not connected
3 4879a?audr?09/05 atr4254 3. pin description 3.1 fmin the input of the fm amplifier, fmin, is a bipolar transitor?s base. a resistor or a coil is connected between fmin and vref2. if a coil is used, the noise performance is excellent. figure 3-1. internal circuit at pin fmin 3.2 gnd1 to avoid cross-talk between am and fm signal s, the circuit has tw o separate ground pins. gnd1 is the ground for the fm part. 3.3 fmgain the dc current of the fm amplifier transistor is adjusted by an external resistor which is con- nected between fmgain and gnd1. to influence the ac gain of the amplifier, a resistor is connected in series to a capacitor between fm gain and gnd1. the capacitor has to shorten frequencies of 100 mhz. figure 3-2. internal circuit at pin fmgain 3.4 agc dc current flows into the agc pin at high fm antenna input signals. this current has to be amplified via the current gain of an external pn p transistor that feeds a pin diode. this diode dampens the antenna?s input signal and protects the amplifier input against overload. the maxi- mum current which flows into the agc pin is approximately 1 ma. in low-end applications, the agc function is not necessary and the external components can therefore be omitted. esd 1 fmin esd 3 fmgain
4 4879a?audr?09/05 atr4254 figure 3-3. internal circuit at pin agc 3.5 agcadj the threshold of the agc can be adjusted by varying the dc current at pin agcadj. if pin agcadj is connected directly to gnd1, the threshold is set to 96 dbv at the fm amplifier out- put. if a resistor is connected between agcadj and gnd1, the threshold is shifted to higher values with increasing resist ances. if agcadj is open, the threshold is set to 106 dbv. figure 3-4. internal circuit at pin agcadj 3.6 fmout the fm amplifier output is an open collector of a bipolar rf transistor. it should be connected to v s via a coil. figure 3-5. internal circuit at pin fmout esd 4 v s agc esd 13 65 k ? agcadj esd 15 fmout
5 4879a?audr?09/05 atr4254 3.7 amin the am input has an internal bias voltage. the dc voltage at this pin is v ref1/2 . the input resis- tance is about 470 k ? . the input capacitance is less than 10 pf. figure 3-6. internal circuit at pin amin 3.8 amout, amout1 the buffered am amplifier consists of a complementary pair of cmos source followers. the transistor gates are connected to amin. the pin amout is the nmos transistor's source, pin amout1 is the pmos transistor's source. due to the two different dc levels of these pins, they have to be connected together via an external capacitor of about 100 nf. this technique can achieve an excellent dynamic range. figure 3-7. internal circuit at pins amout1 and amout 3.9 vref1 vref1 is the stabilized voltage for the am ampl ifier and the agc block. to achieve excellent noise performance at lw frequencies, it is recommended that this pin be connected to ground via an external capacitor of about 1 f. esd 8 470 k ? vref1/2 amin amout1 esd esd amout 11 10
6 4879a?audr?09/05 atr4254 figure 3-8. internal circuit at pin vref1 3.10 vref2 for the dc biasing of the fm amplifier, a sec ond voltage reference circuit is integrated. since the collector current is temperature independent, the output voltage has a negative temperature coefficient of about ?1 mv/k. to stabilize this voltage, an external capacitor to ground of a few nf is recommended. figure 3-9. internal circuit at pin vref2 3.11 gnd2 gnd2 is the ground for the am amplifier. esd 12 vs gnd1 vref1 esd 5 gnd1 vref2
7 4879a?audr?09/05 atr4254 4. functional description the atr4254 is an integrated am/fm antenna impedance matching circuit. it compensates cable losses between the antenna (for example, windshield, roof or bumper antennas) and the car radio, which is usually placed far away from the antenna. the fm amplifier provides excellent noise performance. external components are used to adjust the gain and the input-output matching impedance. therefore, it is possible to adjust the ampli- fier to various cable impedances (usually 50 ? , 75 ? or 150 ? ). to protect the amplifier against input overload, an automatic gain control (agc) is included on the chip. the agc observes the ac voltage at the fm amplifier output, rectifies this signal, and delivers dc current to dampen the input antenna signal via an external pin diode . the threshold for the agc is adjustable. sim- ple and temperature-compensated biasing is possible due to the integrated voltage reference v ref2 . the am part consists of a buffer amplifier. t he voltage gain of this stage is approximately one. the input resistance is 470 k ? , the input capacitance less than 10 pf. the output resistance is 125 ? . an excellent dynamic range is achieved due to the complementary cmos source follower stage. 5. absolute maximum ratings stresses beyond those listed under ?absolute maximum ratings? may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions beyond t hose indicated in the operational sections of this specification is not implied. exposure to absolute maximum rati ng conditions for extended periods may affect device reliability . reference point is ground (pins 2 and 7) parameters symbol value unit supply voltage v s 8.8 v power dissipation, p tot at t amb = 85c p tot 460 mw junction temperature t j 150 c ambient temperature t amb ?40 to +85 c storage temperature t stg ?50 to +150 c electrostatic handling (hbm at esd s.5.1) v esd 1000 v 6. thermal resistance parameters symbol value unit junction ambient r thja 140 k/w
8 4879a?audr?09/05 atr4254 7. electrical characteristics v s = 8v, t amb = 25 c, unless otherwise specified (see figure 7-1 on page 9 ). parameters test conditions pin symbol min. typ. max. unit supply voltage 14 v s 7.2 8 8.8 v supply currents 14 i s 3.5 4.8 5.6 ma reference voltage 1 output (i 12 =0) 12 v ref1 5.1 5.4 5.7 v reference voltage 2 output (i 5 =0) 5 v ref2 2.3 2.6 2.8 v temperature dependence of vref2 5 v ref2 / ? t?1mv/k am amplifier input resistance 8 r amin 470 k ? input capacitance 8 c amin 10 pf output resistance 10 r out 125 ? voltage gain 8, 10 a 0.85 output noise voltage (rms value) s1 switched to 2 b=6khz 150 khz to 300 khz 500 khz to 6.5 khz 10 v n1 v n2 ?2 ?6 dbv dbv 2nd harmonic s2 switched to 1 f amin = 500 khz output voltage = 110 dbv 10 ?65 dbc fm amplifier supply current limit i agc , i agcadj =0a 15 i 15 33 35 ma input resistance f = 100 mhz 1 r fmin 50 ? output resistance f = 100 mhz 15 r fmout 50 ? power gain f = 100 mhz 1, 15 g 5 db output noise voltage f=100mhz b=120khz 15 v n 0dbv 3rd-order output intercept f = 100 mhz 15 132 dbv agc agc input voltage threshold f=100mhz s2 switched to 1; agc threshold dc current is 10 a at pin 4 15 v th1 96 dbv agc input voltage threshold f=100mhz, s2 switched to 2; agc threshold dc current is 10 a at pin 4 15 v th2 106 dbv agc output current agc active i agc 1.2 ma
9 4879a?audr?09/05 atr4254 figure 7-1. test circuit 2 1 2.2 f s1 v s 150 ? 2.2 nf 2.2 nf 51 ? 22 ? 2.2 nf 2.2 h amout 2.2 h 100 nf 2.2 nf fmout 2.2 nf 1 nf 15 pf amin + s2 12 18 9 16 5 k ? i 4 fmin 100 nf v s i 3 i 14 i 15 atr4254
10 4879a?audr?09/05 atr4254 figure 7-2. fm intermodulation distortion 90 95 100 105 mhz input dbv 103 dbv 90 95 100 105 mhz output dbv 108 dbv 58 dbv gain = 5 db agc not active 90 95 100 105 mhz input dbv 118 dbv 90 95 100 105 mhz dbv 100 dbv 50 dbv output agc active
11 4879a?audr?09/05 atr4254 figure 7-3. test circuit for am large signal behavior figure 7-4. am harmonic distortion dut 1 nf f = 500 khz v 0 50 ? lpf amout 115 dbv analyzer f cutoff = 500 khz 100 nf 5 k ? 75 dbv amin r in = 50 ? 100 nf amout1 50 ? 0.5 1.0 1.5 v amout (dbv) 115 dbv 50 70 110 90 55 dbv 45 dbv f (mhz)
12 4879a?audr?09/05 atr4254 figure 7-5. application circuit fm agc am fmin agc amin amout1 vref1 fmout fmgain fmgnd i agc agcadj amgnd vref2 v ref antenna am fm protection circuit output vs pin v s = 8.2v 1 k ? bc558 51 2.2 h r 1 2.2 nf 100 nf 200 nf ba679 2.2 nf 39 pf 2.2 h 2.2 nf 2.2 nf 510 ? 1 f + 2.2 nf v s v 1 nf r 2 100 nf amout r 1 and r 2 depend on used fm cable impedance fm cable impedance r1 ( ? ) 50 75 100 125 150 150 270 390 470 620 22 33 51 86 160 r 2 ( ? )
13 4879a?audr?09/05 atr4254 9. package information 8. ordering information extended type number package remarks atr4254-tbjy so16 ? atr4254-tbqy so16 taping corresponding to ice-286-3 ATR4254-PEPY qfn16 ? atr4254-peqy qfn16 taping corresponding to ice-286-3 technical drawings according to din specifications package so16 dimensions in mm 10.0 9.85 8.89 0.4 1.27 1.4 0.25 0.10 5.2 4.8 3.7 3.8 6.15 5.85 0.2 16 9 18
14 4879a?audr?09/05 atr4254
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