Sundance FC202 FPGA Uživatelský manuál stáhnout pdf (Strana 8)

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2. FC202 QUADRATURE CONVERSION

In order to interface to the FC108-D module for Polyphase filtering, a conversion from real to

quadrature representation is necessary. FC202 firmware module converts real signals to

analytic signals of In-phase and Quadrature (I & Q) components.

The method used is a linear phase conversion technique, based upon the (Parallel) Distributed

Arithmetic FIR Filter LogicCORE

. The basic approach is to approximate the Hilbert

Transform using an FIR filter

. Typically, when such methods are used, a decimate-by-2

operation can be performed without loss of spectral information. Thus, the data rate of the

outputs matches the data rate of the inputs.

The frequency performance of the FC202 is as follows:

Sample Rate 102.4MHz

IF Center 21.4MHz

IF Bandwidth 22.5MHz

IF Span 10.15MHz –

33.65MHz

Passband (Gain=1) 5.12MHz – 46.08MHz

Table 1 - FC202 Frequency Response Characteristics

Hilbert Transform Magnitude and Phase response based on the above parameters is given in

figure 2 while figure 3 shows the XY plot of the Hilbert transform.

The FC202 component represents a pure-FPGA ‘task’, and implements the following interface:

Port Name Valid

Width

Direction Implementation Description

ADC_IN 16 Input FPGA Raw time domain data

DECIMATE_IN 1 Constant FPGA Enable decimation-by-two

I_OUT 16 Output FPGA In-Phase component, time

domain data

Q_OUT 16 Output FPGA Quadrature component, time

domain data

Table 2 - FC202 Interfaces

See: http://www.xilinx.com/ipcenter/catalog/logicore/docs/da_fir.pdf

Remez Exchange or Parks-McClellan Optimal Method

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Sundance FC202 FPGA Uživatelský manuál Strana 8