Sundance FC202 FPGA User Manual
Page 8
Sundance Digital Signal Processing Inc.
Rev1.0
4790 Caughlin Parkway 233, Reno, NV 89519-0907, U.S.A.
Tel: +1 (775) 827-3103, Fax: +1 (775) 827-3664, email:
www.sundance.com
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
2
. The basic approach is to approximate the Hilbert
Transform using an FIR filter
3
. 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
2
See:
http://www.xilinx.com/ipcenter/catalog/logicore/docs/da_fir.pdf
3
Remez Exchange or Parks-McClellan Optimal Method