KA8503 low voltage speech network introduction the KA8503 is a telephone low voltage speech network which includes mic amp. transmit amp, side-tone amp, receive amp. it handles the voice signal performing the 2/4 wire interface and changing the gain on both sending and receiving amplifiers to compensate for line at- tenuation by sensing the line length through the line current. applica- tion dependent parameters such as amplitude of each amp, sidetone level line balance, and frequency response are controlled by exter- nal components. each gain can be controlled by external component exchange. the receiver output driving capability is adjustable. features adjust sending and receiving attenuation length mute function side tone balance network constitution low voltage operating ac impedance matching uses in inexpensive components (5 capacitors & 10 resistors) uses a minimum of external components block diagram fig. 1
KA8503 low voltage speech network pin configuration fig. 2 pin description 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 KA8503 v + txo txi v dd mute gr st1 st2 st3 rxo3 rxo2 rxo1 rxi v - mic2 mic1 mic0 st0 pin no symbol description 1 v + postive power line and transmit amplifier output. 2 txo transmit amplifier output. the resistor which is connected this pin to v - sets dc resistance of the circuit. the value of resistor is suitable for 47 ~ 100 w . 3 txi transmit amplifier input. input impedance is 17k w 20% 4 v dd dc power supply pin. this pin will be connected to a decoupling capacitor 47 m f~ 100 m f. 5 mute mute active high input. 6 gr gain regulation control input. input impedance is 5.5 k w 20%. 7, 8, 9 st1, st2, st3 seperate amplifier control inputs. 10 sto seperate amplifier output. 11 mic0 microphone amplifier output. 12, 13 mic1, mic2 microphone amplifier inputs. input impedance is 1.7 k w 20% 14 v - negative power line. 15 rxi receive amplifier input. 16 rxo1 receive amplifier output. 17, 18 rxo2, rox3 receive amplifier output. output impedance is 3 w ( typ)
KA8503 low voltage speech network absolute maximum ratings electrical characteristics (refer to the test circuits, i l = 15 ~ 100ma, f = 200 ~ 3.4khz, ta = 25 c, unless otherwise specified) characteristic symbol value unit line voltage (3ms max) forward line current reverse line current power dissipation ( ta = 70 c) operating temperature storage temperature v l i lf i lr p d t opr t stg 22 150 -150 1 - 40 ~ + 70 - 55 ~ + 125 v ma ma w c c characteristic symbol test conditions test fig min typ max unit i l = 15ma 3.3 3.7 4.1 i l = 100ma 11 13 15 i l = 20ma 46 48 50 t x gain g v (tx) i l = 38.5ma 4 43.5 45.5 47.5 db i l = 55ma 41 43 45 t x range of regulation d g tx d g tx = g tx1 - g tx3 3 5 7 db v mi = 5mv f = 200hz - - 1 i l = 20ma f = 3.4khz - - 1 v mi = 5mv f = 200hz - - 1 i l = 80ma f = 3.4khz - - 1 i l = 20ma, f = 200hz ~ 3.4khz - 1.5 - i l = 100ma, f = 200hz ~ 3.4khz - 1.5 - i l = 20ma, f = 200hz ~ 3.4khz - 1.5 - i l = 100ma, f = 200hz ~ 3.4khz - 1.5 - t x input impedance z i (tx) i l = 20ma, f = 200hz ~ 3.4khz - 1.7 - k w mute input current i i (mute) i l = 20ma i m = 0.1ma 0.1 - - ma i l = 20ma -13.5 -11.5 -9.5 r x gain g v (rx) i l = 38.5ma 5 -16 -14 -12 db i l = 55ma -18.5 -16.5 -14.5 r x range of regulation d g rx d g rx = g rx1 - g rx3 3 5 7 db v ri = 0.5v f = 200hz - - 1 i l = 20ma f = 3.4khz - - 1 v ri = 0.5v f = 200hz - - 1 i l = 80ma f = 3.4khz - - 1 f = 200hz 0.3 0.5 - f = 3.4khz 0.3 0.5 - f = 200hz 0.3 0.5 - f = 3.4khz 0.3 0.5 - i l = 20ma f = 200hz - 0.9 - v ri = 10v f = 3.4khz - 0.9 - line voltage t x frequency response t x dynamic output voltage r x frequency response r x dynamic output voltage r x max output voltage v l d g tx (res) v o (tx) t x max output voltage v otx (max) d g rx (res) v o (rx) v orx (max) v 4 4 4 4 5 5 5 vp-p vp-p db db vp-p vp-p v ri = 0.5v f = 1khz i l = 20ma i l = 100ma v mi = 5mv f = 1khz
KA8503 low voltage speech network test circuit fig. 3 fig. 4 fig. 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 KA8503 a i l + line 910 w 470uf 1.5m 12k 62k 47uf 6.2k mute 300 w 20uf 1.7k sw1 v m1 d 47uf 1.5m 1.5m 18k 27k 104 75 w 3.6k 820 w 9.1k 22uf 10 560 w 310 w sw3 v ri 600 w 62k c 350 w sw2 - line 470uf a b c d e f g v mi 470uf v ro v so 560 KA8503 w a b c d e f g 470uf v ro v ri 560 KA8503 w *sw 1 : - *sw 2 : on *sw 3 : - *sw1: off *sw2: on *sw3: ? *g v (rx) = 20 log v ro v mi v so v mi v so v ri *side tone = 20 log * g v(tx) = 20 log
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