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APPLICATION NOTE
ST75C52/ST75C520 - SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
CONTENTS
I II II.1 II.2 II.3 III III.1 III.2 III.3 III.4 IV V VI VII VIII INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FEATURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TRANSMISSION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RECEPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POWER SUPPLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTRICAL SCHEMATIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RETURN LOSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . TRANSMIT GAIN . . . . . . . . . . . . . . . . . . . . . . . . . . RECEIVE GAIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . DUPLEXER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................ ............................ ............................ ............................
Page
1 1 1 1 1 2 2 2 2 2 3 3 3 5 6
OUTPUT LEVELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PCB GUIDE LINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OUT OF BAND POWER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PERFORMANCES AT 14400bps (V.17) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I - INTRODUCTION The ST75C52/520 uses basically a hybrid interface which allows to receive a V.17 signal between 0dBm and -45dBm with very good performances (see test report of the ST75C52/520). Such hybrid interface is perfect for high end equipment. The drawback is that the user has to use 4 operationnal amplifiers rather than 3 usally. As some manufactuers need to reduce the cost of their design we are going to introduce in this application note a simpler hybrid circuit which will save cost but also provide high performances. II - FEATURES II.1 - Transmission The hybrid will use the differential output TXA1 and TXA2 of the ST75C52/520.
AN823/0695
The nominal output level for each tone and each carrier must be equal to 0dBm when no attenuation is selected in the ST75C52/520 (default setting of the ST75C52/520).
II.2 - Reception The hybrid will only use the RXA1 input of the ST75C52/520 rather than RXA1 and RXA2 differential inputs in the basic hybrid. The far end carrier (modem signal) can be received between -1dBm and -44dBm.
II.3 - Power Supply Uses only one +12V power supply.
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SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
III - ELECTRICAL SCHEMATIC The Figures 1 and 2 show the complet electronic used (ST75C52/520 connection and its hybrid interface). As the telephone line interface is particular for each country we did not provide it on the figure. The return loss is adjusted by the following components : R5, C7 and C8 (the values will change if the reference impedance change). In our example the reference impedance is a 600 resistor. The 2 wires to 4 wires part (duplexer) is obtained by R6, R7, R8 and R9. The rejection of the unwanted signal (transmit signal at the RXA1 Pin) is equal to 30dB which is enough for the full duplex modulations V.21, V.23 and BELL 103. The transmit gain is fixed by the ratio R4/R3 and is adjusted to have an output level at 0dBm on 600 w h en n o a t t e nu a t i on is sel ect ed i n t he ST75C52/520. A filter at 9.6kHz is installed on the TXA1 and the TXA2 output. The receive gain is fixed by the ratio R9/R8 and must be adjusted each time the customer changes is telephone line interface components (mainly the transformer could have an insertion loss between 1 and 2dB). The received signal is connected to RXA1 input and RXA2 input is tied to VCM. The signal at RXA1 must not be higher than 2.5V. The tuning of such a hybrid interface could be done as indicated below : - adjust your telephone line interface (DC current...), - adjust the return loss, - adjust the transmit gain, - adjust the receive gain, - adjust the duplexor. Note : an iteration between step 4 and 5 could be necessary. III.1 - Return Loss Adjust R5, C7 and C8 to meet the technical requirements in your country which imposes the reference impedance (600 or complex impedance), and the different parameters as DC voltage and DC current on the line. III.2 - Transmit Gain We recommand the following procedure : - keep the SETGN default value (0x7FFF) which selects no attenuation on the transmit signal, - adjust the ratio R4/R3 to have 0dBm, - adjust the attenuation (parameter of the SETGN command) for each signal which will be sent by the ST75C52/520. We suggest to adjust the output level at -9dBm for the tones and the carriers. For the DTMF we suggest an output level equal to -4.4dBm. The method to compute the SETGN 's parameter is : - no attenuation parameter equals to 0x7FFF (hexa decimal value), - convert this value in decimal 32767, - multiply 32767 by the absolute decimal value of the wanted attenuation (usally you know it in dB, so you must convert dB to absolute value), - convert the result in hexadecimal, you have now the parameter of the SEGTN command.
Example : Parameter for an attenuation equal to -10dB or a gain equal to 0.3162. SETGN 's parameter in decimal value = 32767 x 0.3162 = 10361 SETGN 's parameter in hexadecimal value = 0x2879.
There is no limitation when using SETGN command, you can make a very fine tuning which is not necessarily equal to 1dB. III.3 - Receive Gain Adjust the ratio R9/R8 to detect carrier at -44dBm. III.4 - Duplexer Adjust the resistors R7 and R6 to remove unwanted carrier when in full duplex mode.
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SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
IV - OUTPUT LEVELS With this hybrid interface the typical output levels for the different carriers when no attenuation is selected (default value for SETGN 's parameter) are :
Carrier Bell 103 Answer Bell 103 Originate V.21 Answer V.21 Originate V.23 Answer V.23 Originate V.27 ter V.29 V.17 V.33 V.21 Channel 2 Level (dBm on 600) 0.88 0.97 0.8 1.1 0.65 0.87 0.44 0 0 0 0.8 Gain (dB) 0 -1 -2 -3 -4 Gain (Hex) 7FFF 7214 65AC 5A9D 50C3 Gain (dB) -5 -6 -7 -8 -9 Gain (Hex) 47FA 4026 392C 32F5 2D6A Gain (dB) -10 -11 -12 -13 -14 Gain (Hex) 287A 2413 2026 1CA7 198A
V - PCB GUIDE LINE For that application note we use a two layers board. Analog (AVDD) and digital (DVDD) power supplies are connected together. The capacitors used for the power supply (DVDD, AVDD) decoupling are installed as close as possible to the power pins. The capacitors used for the voltage refence (between VREFP/VCM and VREFN/VCM) are connected as close as possible to the pins. Both analog ground AGNDR and AGNDT must be connected with very low impedance to a single point. The 2.2nF connected beween RXA1 and RXA2 Pins must be as close as possible to them. Provide a ground grid in all around and under components on both sides of the band and connect them to avoid small islands.
In the same conditions the output levels for the tones are :
Tones DTMF 0 DTMF 1 DTMF 2 DTMF 3 DTMF 4 DTMF 5 DTMF 6 DTMF 7 DTMF 8 DTMF 9 Level (dBm on 600) -0.35 -0.3 -0.35 -0.4 -0.35 -0.35 -0.4 -0.3 -0.35 -0.4 Tones DTMF A DTMF B DTMF C DTMF D DTMF * DTMF # 2100Hz 1650Hz 2225Hz 1300Hz Level (dBm on 600) -0.47 -0.47 -0.47 -0.47 -0.3 -0.35 0.15 0.52 0 0.75
VI - OUT OF BAND POWER This hybrid (Figure 2) needs a filter in the transmit side to avoid out of band power due to the sigma delta convertors. Two one pole filters are used. The first is built around the MC33174 operational amplifier (Pin 1, 2, 3) with the R3, R4, C4, R2, R1, C1 components (Fc is equal to 9.6kHz). The second pole is introduced with C7 in parallel with the line transformer. In that case the out of band power (frequencies above 4kHz) is 60dB lower than the in band power.
To adjust the factory output level of your equipment use the SETGN command as explain on Chapter III. We simply recall the parameters for typical attenuation (see Table below).
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SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
Figure 1
(third harmonic series resonance oscillator) C1 is optionnal 29.4912MHz Y1 L1 1H C2 33pF C3 10nF +5VA
C1 5pF
* C4
100nF
C5 10F
43 SCCLK
49 EOS
EXTAL 56 XTAL 55 HALT/NOP 53 TXA1 TXA2 +5V TXA1 TXA2 DAA
50 BOS 45 RDYS
+5V +5V
2 1
51 SCOUT 42 SCIN 44 MCI
RXA1 60 RXA2 61
RXA1
R8 470
R7 10k
54 CLKOUT 48 MC0 47 MC1 46 MC2
AVDD 62 VREFP 58 VCM 63 VREFN 57 AGNDR 59
D0 D1 D2 D3 D4 D5 D6 D7 DTACK INTR Microcontroller CS SR/W (WR) SDS (RD)
26 SD0
27 SD1
28 SD2 29 SD3 30 SD4 31 SD5 32 SD6 33 SD7
AGNDT 64
ST75C52 ST75C520
EYEX EYEY EYESYNC EYECLK
7 6 4 5
TP1 TP2
37 SDTACK 38 SINTR 36 SCS 35 SR/W
34 SDS
* C9
100nF TXD 16 CLK 14 RXD 15 CD 13 RTS 11 CTS 12 RING 10 (connect close to the ST75C52) TxD RxD DGND
C10 10F VCM
* C8
100nF
39 INT/MOT
A0 A1 A2 A3 A4 A5 A6 RESET +5V +5V INTEL mode MOTOROLA mode (select one of the two)
C11 10F
17 SA0 18 SA1 19 SA2 20 SA3 21 SA4
22 SA5
EBS
3
23 SA6 52 RESET 9
DVDD
8
CLK CD RTS CTS RING V.24/RS232
DGND 24 DGND 40
25 DVDD
41 DVDD
C20 10F
*
C12 10nF
*
C13 10nF
*
C14 10nF
Note : All capacitor with a "*" must be implented close to the ST75C52/520 pin.
4/6
AN823-01.EPS
SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
Figure 2 : Differential Output and Single Ended Reception Uses only One Power Supply
C4 220pF R4 75k 1% MC33174 4 U1D
12 14 13
C3 100nF R3 13k 1%
TXA1
11
MC33174 11 U1A
2 1 3 4
C2 100nF R2 13k 1%
TXA2
R5 560
Transformer T1 C7 22nF 6V
TIP
C1 220pF 6V
R1 75k 1% 6V C6 100nF
C9 1F +12V C5 4.7F R7 30k 1%
TIP and RING must be connected to C8 the telephone line interface which is 22nF particular for each manufacturer.
RING
+12V C14 100nF C13 2.2F R12 47k 1%
10
RXA2
C12 : as closed as possible to the ST75C520 RXA1 and RXA2 Pins.
RXA1
C12 2.2nF 7 R10 1.2k 1% C11 1F
MC33174 U1B 4 5 6 11
R6 10k 1% 6V
MC33174 4 U1C
8 9 11
AN826-02.EPS
R11 47k 1%
6V
R8 10k 1% C10 1F
R9 8.25k 1%
VII - PERFORMANCES AT 14400bps (V.17) We tested this hybrid doing Bit Error Rate Test (BERT) on a TAS equipment. Mainly we did BERT versus different Signal to Noise Ratio (SNR) for various lines. The Figures 3 and 4 show the results on a Flat line (L1) while receiving between -1dBm and -43dBm. The ST75C52/520 begins to make error in reception at a SNR equals to 23dB 1dB. These results are identical to thus obtained with the hybrid which uses the differential inputs RXA1 and RXA2. The Figure 5 shows the result when receiving via European line, US lines and Japanese lines. Also in that case the performances are equal to thus that we obtained with the first hybrid which uses the differential inputs RXA1 and RXA2. Figure 3 :
1 10 10
BERT
-1 -2 -3 -4 -5 -6
AN826-03.EPS
Reception on Flat Line L1 at -1, -3, -6, -9, -20dBm
L1-1 L1-3 L1-6 L1-9 L1-20
10 10 10 10
19
20
21 SNR
22
23
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SINGLE ENDED AND SINGLE POWER SUPPLY HYBRID CIRCUIT
Figure 4 :
1 10 10
BERT
-1 -2 -3 -4 -5 -6
AN826-04.EPS
Reception on Flat Line L1 at -30, -35, -38, -40, -43dBm
L1-30 L1-35 L1-38 L1-40 L1-43
Figure 5 :
1 10 10 10 10 10
-1
BERT on M1040, C1, JPN1
-2
10 10 10 10
BERT
-3
-4
-5
19
20
21 SNR
22
23
24
22 23 24 25 26 27 28 29 30 31 32 SNR
VIII - CONCLUSION This new hybrid interface is simpler than the full differential (differential outputs and inputs) introduced in the Data Sheet. It will be easier for the customer to adjust return loos again complex impedance with this new hybrid. Single power supply is some times necessary to save cost of the power equipment. The performances still remain very good. We suggest this hybrid interface in some application where level has to be transmitted at high level (greater than -9dBm) and where single power supply schematic must be used.
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 licence is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics. (c) 1995 SGS-THOMSON Microelectronics - All Rights Reserved Purchase of I2C Components of SGS-THOMSON Microelectronics, conveys a license under the Philips I2C Patent. Rights to use these components in a I2C system, is granted provided that the system conforms to the I2C Standard Specifications as defined by Philips. SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - China - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
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AN826-05.EPS
M1040 C1 JPN1

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