AD7400 Analog Devices, AD7400 Datasheet - Page 15

• Manufacturer Part Number: AD7400
• Description: Isolated Sigma-Delta Modulator
• Manufacturer: Analog Devices

Specifications of AD7400

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 10MSPS
• Interface: Ser
• Analog Input Type: Diff-Uni
• Ain Range: ± 0.2 V Diff,0.4 V p-p
• Adc Architecture: Sigma-Delta Modulator
• Pkg Type: SOIC

DIGITAL FILTER
A Sinc
filter can be implemented on an FPGA or a DSP. The following
Verilog code provides an example of a Sinc
on a Xilinx® Spartan-II 2.5 V FPGA. This code can possibly be
compiled for another FPGA, such as an Altera® device. Note
that the data is read on the negative clock edge in this case,
although it can be read on the positive edge if preferred. Figure 28
shows the effect of using different decimation rates with various
filter types.
/*`Data is read on negative clk edge*/
module DEC256SINC24B(mdata1, mclk1, reset,
DATA);
input
input
input
filtered*/
output [15:0] DATA;
integer location;
integer info_file;
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [23:0]
reg [15:0]
reg [7:0]
reg word_clk;
reg init;
/*Perform the Sinc ACTION*/
always @ (mdata1)
if(mdata1==0)
to a -1 for 2's comp */
else
/*ACCUMULATOR (INTEGRATOR)
Perform the accumulation (IIR) at the speed
of the modulator.
3
ip_data1 <= 0;
ip_data1 <= 1;
filter is recommended for use with the AD7400. This
mclk1;
reset;
mdata1;
/*used to clk filter*/
/*used to reset filter*/
/*ip data to be
ip_data1;
acc1;
acc2;
acc3;
acc3_d1;
acc3_d2;
diff1;
diff2;
diff3;
diff1_d;
diff2_d;
DATA;
word_count;
/*filtered op*/
/* change from a 0
3
filter implementation
Rev. E | Page 15 of 20
Z = one sample delay
MCLKOUT = modulators conversion bit rate
*/
always @ (negedge mclk1 or posedge reset)
if (reset)
else
/*DECIMATION STAGE (MCLKOUT/ WORD_CLK)
*/
always @ (posedge mclk1 or posedge reset)
if (reset)
else
always @ (word_count)
/*DIFFERENTIATOR (including decimation stage)
Perform the differentiation stage (FIR) at a
lower speed.
Z = one sample delay
WORD_CLK = output word rate
*/
WORD_CLK
MCLKOUT
IP_DATA1
ACC3
begin
acc1 <= 0;
acc2 <= 0;
acc3 <= 0;
end
begin
acc1 <= acc1 + ip_data1;
acc2 <= acc2 + acc1;
acc3 <= acc3 + acc2;
end
/*initialize acc registers on reset*/
/*perform accumulation process*/
word_count <= 0;
word_count <= word_count + 1;
word_clk <= word_count[7];
+
Z
–1
Figure 26. Differentiator
Figure 25. Accumulator
Z
+
–
DIFF1
ACC1+
+
Z
–1
Z
–
+
–
ACC2+
DIFF2
+
Z
–1
Z
AD7400
–
+
ACC3
DIFF3