2019-01-27 GlobeSpan Transmissio

1 Transceiver Design

As we look into the schematics of the GSI transceiver reference design, the filter in the transmission path will be as the Fig.1 shows:

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If we focus on the filter and note that the input signal applied are differential in a complementary (push-pull or balanced) manner,

the half-circuit analysis can be applied and the circuit in Fig.2 is what we can get from the simplification of Fig.1.

From Fig,2, the following relations can be achieved as follows:

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If we define W n as the resonance frequency and** W o** as the 3dB frequency, we can get the following relations:

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We can see from the above equations that the inductor and the capacitor decide the resonance frequency.

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As we investigate the plot of the transfer function, we can see that there is a notch in the frequency about 250~300KHz. If we calculate the resonance frequency using

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The filter is a second-order LCR resonator by itself and its configure is a low-pass filter. The parallel resonance circuit (the shunt circuit of capacitor and inductor) is

used to obtain a pair of transmission zeros on the -axis. These two zeros will introduce a drop around the resonance frequency and makes the slope of the transfer

function sharper.