1、SMPTE 27bM 95 8357401 0002433 427 A 1 SMPTE STANDARD ANWSMPTE 276M-1995 for Television - Transmission of AEWEBU Digital Audio Signals Over Coaxial Cable Page 1 of 4 pages 1 Scope IEC 169-8 (1978), Part 8: R.F. Coaxial Connectors with Inner Diameter of Outer Conductor 6.5 mm This standard describes a
2、 point-to-point coaxial cable (0.256 in) with Bayonet Lock - Characteristic Imped- interface for the transmission of AES/EBU digital audio signals throughout television production and broadcast facilities. 3 Transmission format 50 (TIS (Type BNC), and Appendix A (1993) The purpose of this standard i
3、s to ensure that a level of compatibility exists between signals generated to this standard and analog video equipment, such as nonclamping distribution amplifiers, switchers, cables, and connectors, as normally used in television applications. Signals conforming to ANSI S4.40 balanced AESEBU can be
4、 interfaced to signals conforming to this standard through the use of matching networks. Examples of the use of matching networks in conjunc- tion with this standard are provided, for information purposes only, in annex A. 2 Normative references The following standards contain provisions which, thro
5、ugh reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent edition
6、 of the standards indicated below. ANSI S4.40-1992, Digital Audio Engineering - Serial Transmission Format for Two-Channel Linearly Represented Digital Audio Data (AES-3) The transmission channel code and source code shall be as described in ANSI S4.40. 4 Generator characteristics 4.1 The output of
7、the generator shall be measured across a 75-ohm resistive load connected directly to the output. 4.1.1 The generator shall have an unbalanced output circuit with a source impedance of 75 ohms and a return loss greater than 25 dB over the frequency band 0.1 MHz to 6.0 MHz. 4.2 The peak-to-peak signal
8、 amplitude shall be 1 .O V f 1 O%, when measured across a 75-ohm resistive load. 4.3 The dc offset, as defined by the midamplitude point of the signal, shall be nominally 0.0 V f 50 mV. 4.4 The rise and fall times, determined between the 10% and 90% amplitude points and measured across a 75-ohm resi
9、stive load, shall lie between 30 ns and 44 ns. 4.5 Data jitter of the output signal shall comply with ANSI S4.40. I CAUTION NOTICE: This Standard may be revised or withdrawn at any time. The procedures of the Standard Developer require that action be taken to reaffirm, revise, or withdraw this stand
10、ard no later than five years from the date of publication, Purchasers of standards may receive current information on all standards by calling or I writing the Standard Developer. Printed in USA. CopyngMO 1995 by THE SOCIETY OF American National Standard MOTION PICTURE AND TELEVISION ENGINEERS 595 W
11、. Hartsdale Ave., While Plains, NY 10607 (914) 761-1100 Approved December 1,1995 ANSVCMPTE 2761111-1 995 SMPTE 27bM 95 5 Receiver characteristics 5.1 The receiver shall present an impedance of 75 ohms with a return loss greater than 25 dB over the frequency band 0.1 MHz to 6.0 MHz. 5.2 The receiver
12、shall correctly interpret the data when connected directly to a line driver working at the upper voltage limit specified in 4.2. 5.3 The receiver shall correctly interpret the data when the transmitted signal is attenuated to an eye-height level of 100 mV, due to cable losses. (See annex A for input
13、 sensitivity and interfacing considerations to matching networks conversion between coaxial and balanced twisted-pair transmission formats.) Annex A (informative) Matching network interface considerations A.l This standard is intended primarily for use in specifying systems operating with unbalanced
14、 electrical line drivers and receivers optimized for coaxial cable transmission. Due consideration should be applied when applying the standard to systems featuring matching network passive circuits, such as are commercially available or may be constructed for interfacing balanced 110-R circuits to
15、unbalanced 754 circuits. For additional information on this topic, the reader?s attention is drawn to AES 31D. When integrating coaxial and balanced twisted-pair AESIEBU signals in a television system, the following points should be considered: A.l.l Conversion between balanced 110 R and unbalanced
16、75 51 for use according to thls standard ANSI S4.40 (also referred to as AES-3) provides for an output voltage of a balanced line driver in the range 2 V - 1 O V p-p. Note, however, that the 1992 version restricts the maximum p-p voltage to 7 V. A signal conforming to the 1985 version of the standar
17、d, when converted for unbalanced coaxial transmission via a matching network, must then be attenuated by a ratio of between 1:2 and 1:lO in order to conform to 5.2 of this standard (Vmax = 1.0 V p-p f 10%). (This restriction is specified to ensure that unbalanced coaxial AESIEBU signals can be route
18、d successfully through nonclamping analog video amplifiers.) The particular value of attenuation is decided by the value of the resistive attenuator portion of the matching network. NOTE - Precision resistors (1%) should be used to maintain the return-loss specification cited in this standard. m 835
19、7401 0002434 363 W 6 Equalization Equalization for transmission cable losses is not usually required. When necessary, equalization shall be provided at the link receiver only. 7 Cable The interconnecting coaxial cable shall have a nomi- nal characteristic impedance of 75 ohms over the frequency rang
20、e 0.1 MHz to 6.0 MHz. 8 Connector type The connector shall have mechanical characteristics conforming to BNC as described in IEC 169-8, but may feature an impedance of 75 ohms. A purely resistive matching network Pi attenuator (figures A.1 and A.2) can be applied, but is incapable of providing a sig
21、nal attenuation ratio of less than 1 :2.6 while maintaining the correct load and source impedance. In this case, if the balanced voltage at the input to the matching network is only 2 V p-p, the unbalanced output voltage will be of the order of 770 mV. An impedance transformer in series with an unba
22、lanced T resistive attenuator (figures A.3 and A.4) can provide an output of 1 V p-p with an input level from 2 V - 10 V, while providing loop current immunity. Note that multiple transformer isolated matching networks used in a trans- mission circuit may result in the circuit return loss being degr
23、aded outside the specification cited in this standard. A.l.l.l Examples of balanced to unbalanced matchlng net- works Figures A.l - A.4 are examples of resistive and inductive matching networks that can be applied for conformity to this standard. A 14-dB attenuator (figures A.l and A.3) will provide
24、 good video equipment compatibility for an AESIEBU signal up to 6 V - 7 V p-p (as per AES-3-1992), while an 18-dB attenu- ator (figures A.2 and A.4) should provide compatibility for any AESIEBU level up to 10 V p-p (as per AES-3-1985). In all the examples shown in figures A.l - A.4, a reduction in l
25、ong distance transmission capability will result from the attenuation. This is described in table A.1, which is based on the cable attenuation properties of standard coaxial cable performance at 6 MHz (normally characterized as 0.78 dB1100 ft O 10 MHz). Page 2 of 4 pages SMPTE 27bM 95 = 357403 00024
26、35 2TT ANSUSMPTE 276M-1995 I 1;OQl /150ROGNDjR I 110 R Load irnpedonce = 112 R GND Source impedance = 72l Return loss 25 dB Attenuation = 1:5 (14 dB) Figure A.l - 14-dB resistive attenuator +l ND J 750 Load impedance = 110 i7 Source impedance = 75R Return loss 25 dB Attenuotion 1:5.25 (14.5 de) r+F+
27、i 110n 01 i oGND 2 GND 1 Lood impedance = 110.3 R Source impedance = 75.3l Return loss 25 dB Attenuation 1:8.33 (18.5 dB) Figure A.2 - l&dB resistive attenuator Load impedance = 110 R Source impedance = 75.7R Return loss 25 dB Att en ua ti on 1:8.33 (18.5 dB) Figure A.3 - 144B transformer attenuator
28、 Figure A.4 - l&dB transformer attenuator Table A.l - AESEBU transmission capabilities of described matching networks PERFORMANCE ( 6 MHz) Eye height 14-dB attenuator 18-dB attenuator VIN VOUT Dist. (m) VOUT Dist. (m) 2.0 0.38 600 0.24 400 5.0 0.95 1 O00 0.60 750 7.0 1.33 1100 0.84 900 10.0 1 .go2)
29、1250 1.20 1050 ) Based on additional (cable) attenuation to a minimum eye height of 100 mV at the input of the coaxial receiver. *) Not compatible with analog video equipment. Page 3 of 4 pages ANSVCMPTE 276M-1995 SMPTE 276M 95 8357401 0002436 136 D A.1.2 Conversion between unbalanced 75 R and balan
30、ced 110 52 for use according to this standard The input sensitivity cited in 5.3 of this standard (VIN 100 mV) is designed to compensate for cable attenuation losses of 20 dB from the nominal output voltage specified in 5.2. It should be noted, however, that the minimum eye height at the input to an
31、 unbalanced to balanced matching network must be higher than this to retain conformity to the minimum eye height of 200 mV at the input of a balanced receiver, as specified in ANSI S4.40. Using an L resistive matching network (figure A.5), a volt- age of 320 mV is required on the 75-R input side of
32、the network to render a voltage of 200 mV on the 11 O-R output, in a manner that maintains a sufficient impedance match. As a result, the use of resistive matching networks in circuits designed to feature maximum voltage levels conforming to this standard will result in additional limitations on max
33、imum transmission distances due to cable attenuation. Using an impedance matching transformer (TR = 1:1.211) (figure A.6) requires a voltage of 165 mV on the 7542 input side of the network to render a voltage of 200 mV on the 110-R output. This type of circuit then imparts no significant limitation
34、on maximum transmission distances, unlike the resistive network shown in figure A.5. A.1.2.1 Examples of unbalanced to balanced matchlng net- works In either of the following cases, a return loss of 25 dB cannot be guaranteed. Note that the resistive matching pad will guarantee a return loss higher
35、than the transformer. 62 R 1.211:l I Figure AS - Coaxial to balanced resistive matching network Annex B (informative) Bibliography AES 31D, AES Information Document for Digital Audio Engineering - Transmission of AES-3 Formatted Data by Unbalanced Coaxial Cable Figure A.6 - Coaxial to balanced transformer matching network Page 4 of 4 pages
