1、Ambit Microsystems Corporation,July26, 2001,ADSL Hybrid Circuit 原理及設計介紹,WHY Hybrid ?,Since ADSL is considered to be a full-duplex system, able to Transmit and Receive at the same time, a receiver must be incorporated into the design. The most common way of accomplishing this is to use a hybrid netwo
2、rk. The hybrids function is to cancel out the transmit signal while still being capable of receiving the signals,The Hybrid Function, Bridge circuit allowing full-duplex operation Transmit signals pass through to line Transmit signals blocked from receive path Receive signals allowed through to rece
3、iver Needs to match line impedance Not ideal Frequency dependant Line dependant,Differential Hybrid Circuit, Resistive elements can be replaced with R, C combinations to better match the line Matching line impedance is critical for rejection of Tx signal Practical Tx rejection in Rx path is 6-20 dB
4、Multiple winding XFRM also can be used,GSV Hybrid Circuitry,Noise Analysis on Active Part,Transmit BufferLine DriverHybrid Receiver,Amplifier Noise Sources (1),eIN -op amp equivalent input noise (data sheet)IP,IN -Op amp input current noise (data sheet)eRx -resistor thermal noise(4kTR),Amplifier Noi
5、se Sources (2),Contribution at the output eIN x (1+R2/R1) IP x Rsource x (1+R2/R1) IN x R2 eR2 eR1 x (R2/R1) eRS x (1+R2/R1)Total at the output is the square root of the sum of the squares,Transmit Buffer (1) Design Concept,Amplifier purpose: 1) Buffer the signal coming from the CODEC 2) Apply a gai
6、n 3) Drive into a passive 3rd-order LPFKey parameters: 1) Low Noise 2) Single Supply +5V operation 3) Low Distortion,Transmit Buffer (2) Block Diagram,Transmit Buffer (3) GSV Design,Transmit Buffer (4) Simplified Circuit,Transmit Buffer (5) System Noise,Line Driver (1) Design Concept,Amplifier purpo
7、se: 1) Apply a gain 2) Drive +13dBm signals (f = 25kHz to 140kHz) through a 1:2 transformerKey parameters: 1) Low Noise 2) Single Supply +12V operation 3) Low Distortion 4) High output current,Line Driver (1) Block Diagram,Line Driver (2) GSV Design,Line Driver (3) Simplified Circuit,Line Driver (4) System Noise,Receiver Amplifier,Homework,Please use above figure to ProveWhen TX signal is present, +RXOUT = 0 iff ZL = 2R1 and RS = ZL,
