TP5700A Telephone Speech Circuit General Description Features The TP5700A is a linear bipolar device which includes all the functions required to build the speech circuit of a telephone. It replaces the hybrid transformer, compensation circuit and sidetone network used in traditional designs. When used with an electret microphone (with integral FET buffer) and dynamic receiver, superior audio linearity, distortion and noise performance are obtained. Loop attenuation compensation is also included. The low voltage design enables the circuit to work over a wide range of operating conditions, including long loops, extension telephones and subscriber carrier applications. Operating power is derived from the telephone line. Y Y Y Y Y Y Y Y Y Y 5 mA – 120 mA loop operation Voltage swing down to 1.0V Electret microphone amplifier Receive amplifier with push-pull outputs Automatic gain compensation for loop length Sidetone impedance independent of input impedance DTMF interface with muting Voltage regulator outputs for DTMF generator etc. Works in parallel with a standard phone on 20 mA loop Available in small outline surface mount package Simplified Block Diagram TL/H/5201 – 1 C1995 National Semiconductor Corporation TL/H/5201 RRD-B30M115/Printed in U. S. A. TP5700A Telephone Speech Circuit December 1989 Absolute Maximum Ratings Operating Temperature, TA If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. V a with Respect to Vb Voltage at Any Other Pin b 25§ C to a 70§ C Power Dissipation (Note 3) 1W b 65§ C to a 150§ C Storage Temperature, TS Junction Temperature 150§ C Lead Temperature (Soldering, 10 seconds) 300§ C 20V V a a 0.3V to Vb b 0.3V DC Electrical Characteristics Unless otherwise specified, all tests based on the test circuits shown in Figure 1 , all limits printed in bold characters are guaranteed at TA e 0§ C to a 60§ C by correlation with 100% testing at TA e 25§ C. All other limits are assured by by correlation with other production tests, and/or product design and characterization. Symbol VT-R VI Parameter Conditions Tip-Ring Voltage including nominal 1.4V polarity guard (See Figure 1 ) ILOOP e 5 mA e 20 mA e 50 mA e 80 mA e 120 mA Minimum Instantaneous Voltage Swing V a to Vb ILOOP e 5mA Min Typ Max 2.8 Units 7 10.5 15 V V V V V 1.0 V 4.5 TRANSMIT AMPLIFIER RXIN Input Resistance From Pin 7 to Vb 15 30 50 kX GXA Gain at 1 kHz RAGC e 0X to Vb ILOOP e 20 mA, TA e 25§ C only 33 35 37 dB g1 dB GXT Gain Variation v. TA GXI Gain Variation v. ILOOP ILOOP e 20 to 100 mA b6 NX Transmit Noise MIC IN1 e 0V 12 18 S/DX Signal/Total Harmonic Distortion ILOOP t 20 mA VL e 800 mVrms 2 10 GXM Gain Change when MUTED MUTE IN t VMON b 55 dB dBrnC % dB DTMF AMPLIFIER RDIN Input Resistance From Pin 8 to Vb GXD Gain at 1 kHz RAGC e 0X to Vb ILOOP e 20 mA, TA e 25§ C only 10 20 55 kX S/DXD Signal/Total Harmonic Distortion ILOOP e 20 mA VL e 1.06 Vrms, TA e 25§ C only 3.5 5.5 7.5 dB 3 10 % GXDT Gain Variation v. TA g1 dB GXDI Gain Variation v. ILOOP ILOOP e 20 to 100 mA b6 dB IMIN Input Current Pin 9 e 1.5V 40 VMOFF MUTE OFF Input Voltage VMON MUTE ON Input Voltage MUTE INPUT mA 0.5 1.5 2 V V DC Electrical Characteristics (Continued) Unless otherwise specified, all tests based on the test circuits shown in Figure 1 , all limits printed in bold characters are guaranteed at TA e 0§ C to a 60§ C by correlation with 100% testing at TA e 25§ C. All other limits are assured by by correlation with other production tests, and/or product design and characterization. Symbol Parameter Conditions Min Typ Max Units 20 35 55 kX b4 b 2.5 dB RECEIVE AMPLIFIER RRIN Input Resistance From Pin 12 to Vb GRA Gain at 1 kHz RAGC e 0X, MUTE IN s VMOFF ILOOP e 20 mA, TA e 25§ C only GRT Gain Variation v. TA GRI Gain Variation v. ILOOP ILOOP e 20 to 100 mA GRM Gain Change when MUTED MUTE IN t VMON NR Receive Noise S/DR Signal/Total Harmonic Distortion VRC Output Clipping Level ILOOP t 20 mA 1 VROS Output Offset Voltage b 5.5 g 0.5 dB b6 b 15 dB b 20 b 23 dB VRCVIN e 0V 0 10 dBrnC VR e 200 mVrms ILOOP t 20 mA 2 10 % Vp-p g 100 mV SIDETONE CHARACTERISTICS STC Sidetone Cancellation at 1kHz 20 mA s ILOOP s 100 mA, (Note 2) 11 15 dB 2 3 3.2 V V 200 2.7 mA mA VOLTAGE REGULATOR OUTPUTS VREG1 Output Voltage, Pin 10 ILOOP t 20 mA MUTE IN s VMOFF MUTE IN t VMON IREG1 Maximum Output Current, Pin 10 MUTE IN s VMOFF MUTE IN t VMON VREG2 Output Voltage, Pin 11 ILOOP t 20 mA 1.1 1.2 V IREG2 Maximum Output Current, Pin 11 ILOOP t 20 mA 300 500 mA TL/H/5201 – 3 TL/H/5201 – 2 1b. Test Circuit for Receive 1a. Test Circuit for Transmit and Sidetone FIGURE 1. Test Circuits for Electrical Characteristics Note 1. Adjust VDC to set specified ILOOP current. Note 2. To measure Sidetone Cancellation, set oscillator in Fig. 1a for VL e 100 mVrms; measure VS. Then in Fig. 1b set oscillator e 100 mVrms; measure VR. STC e 20log VR/VS. Note 3. For operation above 25§ C, the device must be derated based on a 150§ C maximum junction temperature and a thermal resistance of 70§ C/W junction to ambiant. MICROPHONE AMPLIFIER A single-ended input amplifier on the TP5700A enables a low cost electret microphone to be used. This provides superior distortion, linearity and noise performance compared to a traditional carbon microphone. The electret should be capacitively coupled to the amplifier input. The acoustic sensitivity of the microphone is intended to be in the range of b60 to b70 dBV/mBar. Loss can be inserted if required by adding a resistive potentiometer either at MIC IN1 or the connection between the pre-amp output and driver stage input. The driver stage pro- Functional Description The TP5700A Telephone Speech Circuits are powered from the telephone Tip and Ring terminals via a full-wave rectifier bridge to protect against loop polarity reversals. The devices provide the following functions: LINE REGULATOR A DC regulator sinks current from the loop in order to maintain a DC slope resistance similar to that of a standard phone. RDC provides an adjustment for the slope resistance. 3 DTMF AMPLIFIER Functional Description (Continued) An additional transmit amplifier is included to enable the open-emitter output of a conventional DTMF generator to be connected to the line via the transmit output stage. This path includes the transmit AGC section. When the MUTE input is pulled high, the DTMF input is enabled and the MIC input disabled. When MUTE IN is open-circuit or pulled to Vb the DTMF input is switched off and the MIC input is enabled. vides automatic gain compensation to reduce the gain as loop length decreases. The AGC range can be adjusted by means of RAGC to limit the maximum loss on a short loop from 0 to 6 dB. RECEIVE AMPLIFIER This buffer amplifier provides the necessary gain or loss for the receive signal. RCV IN should be AC coupled to SIDETONE (pin 4). Automatic gain control is built into the amplifier to reduce the gain as loop length decreases. The AGC range is adjusted in common with the transmit AGC range with a range of adjustment for maximum loss from 0 to 6 dB. Push-pull complementary outputs provide balanced direct drive to a dynamic transducer, which may have an impedance as low as 100X. The effective receive gain can be reduced by adding a resistor in series with the transducer. The receive gain is automatically reduced by 20 dB when the MUTE input is pulled high. VOLTAGE REGULATOR OUTPUTS A precision band-gap voltage reference controls a regulator to provide bias for internal circuits. Two auxiliary outputs are also available. VREG1 is provided specifically for powering a low voltage pulse dialer or DTMF generator. In order to protect this output in low voltage situations where the instantaneous voltage across the Speech Circuit may swing below the VREG1 output voltage, an internal switch controls the maximum available output current. In speech mode, MUTE IN is low, VREG1 output will track approximately (/2 the TipRing voltage and the available output current is limited to 200 mA. This is adequate to power a DTMF generator in standby mode. When MUTE IN is pulled high to switch the Speech Circuit to the DTMF dialing mode, VREG1 is switched to a 3V regulated output and up to 2 mA may be drawn from it to power the active DTMF generator. A 1.2V regulated output is also provided at VREG2 to power a low voltage 2-wire electret microphone such as the Primo EM80-PMI2. SIDETONE CIRCUIT The level of Sidetone cancellation may be adjusted by connecting an external balance impedance to SIDETONE (pin 4) and coupling this point to V a . For good sidetone cancellation the balance impedance should be approximately 10 times the subscriber line input impedance. Some typical component values to match a precise 600X termination for test purposes are shown in Figure 2. Use the component values shown in the Applications Section for better results over a wide range of telephone line impedances. TL/H/5201 – 4 * See Figure 3 Note: ZBAL circuit shown is for test purposes with a resistive line termination. See Applications Information for suggested component values for normal reactive line applications. FIGURE 2. TP5700A Telephone Speech Circuits 4 Connection Diagram Dual-In-Line Package TL/H/5201 – 5 Top View Order Number TP5700AM or TP5700AN See NS Package M16B or N16A Pin Descriptions Pin 12 RCV IN The receive AGC amplifier input. Pin 13 V a Pins 1, 2 RCV0 a and RCV0b The push-pull complementary outputs of the receive amplifier. Dynamic transducers with a minimum impedance of 100 X can be directly driven by these outputs. Pin 3 Vb This is the positive supply input to the device and should be connected to the positive output of the polarity guard. The current through this pin is modulated by the transmit signal. Pin 14 RDC This is the negative supply input to the device and should be connected to the negative output of the polarity guard. All other voltages on the device are referred to this pin. Pin 4 S/T This is the output of the Sidetone cancellation signal, which requires a balance impedance of approximately 10 times the subscriber’s line impedance to be connected from this pin to V a (pin 13). Pin 5 XDI The input to the line output driver amplifier. Transmit AGC is applied in this stage. Pin 6 XPO This is the transmit pre-amp output which is normally capacitively coupled to pin 5. Pin 7 MIC IN1 An external 1W resistor is required from this pin to Vb to control the DC input impedance of the circuit. The nominal value is 56X for low voltage operation. Values up to 82X may be used to increase the available transmit output voltage swing at the expense of low voltage operation. Pin 15 VBIAS This internal voltage bias line must be connected to V a via an external resistor, Ro, and decoupled to Vb with a 22 mF capacitor. Ro dominates the AC input impedance of the circuit and should be 620X for a 600X input impedance or 910X for a 900X input impedance. Pin 16 RAGC The range of transmit and receive gain variations between short and long loops may be adjusted by connecting a resistor from this pin to Vb (pin 3). Figure 3 shows the relationship between the resistor value and the AGC range. This pin may be left open-circuit to defeat AGC action. This is the inverting input to the transmit pre-amplifier and is intended to be capacitively coupled to an FET-buffered electret microphone. Pin 8 DTMF IN The DTMF input which has an internal resistor to Vb to provide the emitter load resistor for a CMOS DTMF generator. This input is only active when MUTE IN (pin 9) is pulled high. Pin 9 MUTE IN The MUTE Input, which must be pulled at least 1.5V higher than Vb to mute MIC IN and enable DTMF IN. Pin 10 VREG1 The regulated output for biasing a pulse dialer or DTMF generator. A 4.7 mF decoupling capacitor to Vb should be fitted if this output is used. Pin 11 VREG2 TL/H/5201 – 7 A 1.2V regulated output suitable for powering a low-voltage electret microphone. A 1mF decoupling capacitor to Vb should be fitted if this output is used. FIGURE 3 5 Applications Information erating voltage ranges. There are four methods of powering the microphone. The TP5700A and TP5700 are flexible circuits designed with several user adjustments to enable the performance to be optimized for different applications. The choice of transducer types and the cavities in which they are mounted will also greatly influence the acoustic performance of the telephone. Some of the consequences of circuit adjustments are as follows: 1. The 1.2V VREG2 output provides the lowest voltage method for microphones rated down to 1V. VREG2 must be decoupled with a 1 mF capacitor to ground. (See Figure 5 .) 2. If VREG1 is not required for DTMF generator operation, it may be used to provide up to 200 mA for microphone power. 3. VBIAS (pin 15) may be used as a decoupled, but unregulated, supply for electrets requiring a higher operating voltage than VREG1 or VREG2. The additional current drawn through Ro will, however, raise the minimum operating voltage of the Speech Circuit. If this method is used the decoupling capacitor must be increased to at least 100 mF to maintain good low frequency return loss. (See Figure 4 .) 4. An electret type with a good power supply rejection ratio can be powered from V a , or a regulated and decoupled supply dropped from V a . RDC ADJUSTMENT 56X is the recommended value for RDC if it is required to meet a maximum Tip-Ring voltage of 4.5V on a 20 mA loop (assuming no more than 1.4V is dropped across the polarity guard). If a higher Tip-Ring voltage is acceptable, RDC may be increased, which will provide a small increase in the available transmit output voltage swing before clipping occurs. RDC should be less than 82X to avoid exceeding the maximum rated voltage on a short loop. RAGC ADJUSTMENT The available AGC range is more than adequate to compensate for the loss of most loops. RAGC should be chosen only to partly compensate for the anticipated maximum loop loss, as over-compensation may tend to exaggerate the variations of sidetone with loop length. TONE DIALING TELEPHONE Figure 4 shows the TP5700 directly interfacing to a low voltage DTMF generator. VREG1 supplies the necessary 2V minimum bias to enable the low voltage tone dialer to sense key closures and pull its MUTE output high. VREG1 then switches to a 3V regulated output to sustain the Tone Dialer during tone generation. The TP5700A DTMF input incorporates the necessary load resistor to Vb and provides gain plus AGC action to compensate for loop length. A muted tone level is heard in the receiver. For DTMF generators with a higher output level, a resistive potentiometer should SIDETONE ADJUSTMENT The component values used for ZBAL should be selected to provide a clear sidetone sound without excessive ‘‘hollowness.’’ The capacitor value and ratio of the two resistors will fix the pole location. To avoid reducing the low voltage performance of the circuit the sum of the two resistors should not exceed 10 kX. POWERING ELECTRET MICROPHONES Electret microphones with integral FET buffers are available in both two-wire and three-wire versions and a range of op- TL/H/5201 – 8 FIGURE 4. Typical Tone Dialing Telephone 6 Applications Information (Continued) VREG1 is used in its non-regulated mode and its output voltage may fall to 2V on a 20 mA loop. A 100 mF decoupling capacitor is required to hold up the pulse dialer supply voltage during dialing. This capacitor will take about one second to charge up when the telephone is first connected to the line, but thereafter the 20 MX resistor required to retain the last-number dialed memory will keep this capacitor charged. Partial muting is obtained by directly connecting the N-channel open-drain MUTE output of the pulse dialer to the RCV IN pin on the Speech Circuit. A fully muted pulse dialer design requires the use of a shuntmode dialer. be added to reduce the level at the speech circuit DTMF Input. For application requiring higher DTMF level, the signal swing across the device can be raised by using 620X in series with 270X for RO. The 270X has to be bypassed by a 10 mf capacitor in order to maintain same AC off hook impedance. PULSE DIALING TELEPHONE The TP5700A can reduce the number of components required to build a pulse dialing telephone, as shown in Figure 5 . The usual current source can be eliminated by using the VREG1 output to power a low-voltage (1.7V) series mode pulse dialer via a blocking diode. A low forward-voltage drop diode such as a Schottky type is necessary because TL/H/5201 – 9 *Low voltage drop diode (e.g. Schottky) ² Low leakage type Ý Indicates National Semiconductor discrete transistor process number FIGURE 5. Typical Pulse Dialing Telephone 7 TP5700A Telephone Speech Circuit Physical Dimensions inches (millimeters) Lit. Ý113984 Order Number TP5700AM NS Package Number M16B Molded Dual-in-Line Package (N) Order Number TP5700AN NS Package Number N16A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Europe Fax: (a49) 0-180-530 85 86 Email: cnjwge @ tevm2.nsc.com Deutsch Tel: (a49) 0-180-530 85 85 English Tel: (a49) 0-180-532 78 32 Fran3ais Tel: (a49) 0-180-532 93 58 Italiano Tel: (a49) 0-180-534 16 80 National Semiconductor Hong Kong Ltd. 13th Floor, Straight Block, Ocean Centre, 5 Canton Rd. Tsimshatsui, Kowloon Hong Kong Tel: (852) 2737-1600 Fax: (852) 2736-9960 National Semiconductor Japan Ltd. Tel: 81-043-299-2309 Fax: 81-043-299-2408 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.