Dynamically Reconfiguring of the Field Programmable Analogue Array AN221E04
Kerstin Eckstein, Peter Möhringer
Faculty of Electrical Engineering
University of Applied Sciences
Fachhochschule Würzburg - Schweinfurt
D-97421 Schweinfurt, Ignaz-Schön-Str. 11
kerstin.eckstein@gmx.de
pmoehrin@fh-sw.de
ABSTRACT
The intention of this paper is to give a short description of the dynamically reconfiguring procedure for a Field Programmable Analogue Array
(FPAA) AN221E04 by means of a tested example.
[1]
I. INTRODUCTION
Fig. 1: Block circuit of an AN221E04 [6]
B.
Switched Capacitor Technique
Digital processing of analogue signals like temperature, pressure, distance, etc. often demand preprocessing by analogue circuits. But analogue circuits in
common have a strong lack in precision and flexibility. The design, even if done by CAD, in many
cases yields poor performance and long alignment
procedures. Even, the need for a redesign can be the
disappointing result. Flexibility can be gained only
for a few simple parameters and adaptive system
matching is more or less impossible. But in between, the Field Programmable Analogue Array
(FPAA) technology helps to avoid these annoying
experiences and opens a new variety in applications. [2,3,4,6]
Following Ohm’s law, the current in resistor R of
the circuit on the left is:
II. TECHNICAL BASES
The circuit on the right hand side shows the principle of the switched capacitor (SC) technique. Voltages U1 and U2 are alternating connected to the
capacitor C by the switch.
A.
Technical Bases of FPAAs
Field Programmable Analogue Arrays (FPAAs) are
based on configurable analogue blocks (CAB) consisting of operational amplifiers, passive elements
and a programmable connecting network. The tolerances of the tested time discrete system, using
switched capacitor technique to implement the
desired analogue functions, only depend on the
ratios of capacitors. So, tolerances down to 0.1%
are achieved easily. CABs can be combined to
configurable analogue modules (CAMs). CAMs are
highly qualified circuits such as filters, integrators,
amplifiers etc. The configuration of the CAMs is
provided in a library by the producer. Fig. 1 shows
the block circuit of the tested FPAA, the Anadigm
AN221E04.
IR =
U1 − U 2
R
(1)
Fig. 2: Comparison between resistor and switched
capacitors [2,4]
Q = C ⋅U c
I =
∆Q
T
(2)
(3)
Using (2) and (3) we determine the transported
amount of capacitor charges within a clock period.
See (4).
∆Q = C ⋅ (U1 − U 2 )
(4)
In case voltages U1 and U2 nearly stay constant
within a clock period, the average current Ī can be
made equal to the current in R if R is chosen after
(7). See also (5), (6).
III. STATIC CONFIGURATION
The programming process is as follows:
Example “FilterBiquad”
IR = I
(5)
U1 − U 2 ∆Q
=
R
T
(6)
T
1
=
C fc ⋅ C
(7)
R=
●
Go to the provided library (Edit | Insert
new CAM or use button
lib)
to open the
The performance of the CAM is defined either by
the capacitor C or the clock frequency fc. [5]
C.
AN221D04 Evaluation Board
The tested FPAA is integrated on an evaluation
board providing two in- and outputs and a serial RS
232 link. The programming data is stored in an onchip SRAM, loaded via the serial link, or by
EEPROM for stand alone purposes.
Fig. 4: Library of existing CAMs
●
●
Choose a proper CAM (e. g. choose the
CAM FilterBiquad and place it on the
sheet)
Determine the necessary parameters (e. g.:
for a Cauer low pass filter of 2. order, Corner Frequency 1.23134 kHz, Gain
0.944061 and Quality Factor 0.863721)
Fig. 3: Evaluation Board AN221D04 [6]
D.
Development Software
The Anadigm company provides the development
software AnadigmDesigner2. It is used for the easy
design of static FPAA configurations. Data files for
stand alone purposes can be created and, in case of
programming dynamic configurations, C++ projects
can be installed also.
Fig. 5: Setting of the CAM Parameter [1]
●
●
Now setting the parameters (double clicking on the CAM opens the window for the
parameters, insert corner frequency, gain,
quality factor and confirm by OK)
Then connect filter input to InputCell3 and
filter output to OutputCell1.
shall be send to the evaluation board using the
Download button. Then, the reconfiguration data is
send, any time the push bar is used for changing the
configuration.
Fig. 8: Lowpass filter with variable parameters
In the frame of a diploma thesis [1] examples were
programmed, e. g.:
Fig. 6: Wiring input and output
●
For static configuration only the data has
to be send to the evaluation board. Do it by
pushing button
or by using the menu
(Configure | Write configuration data to serial port)
IV. DYNAMIC CONFIGURATION
For dynamic configuration the steps of static configuration have to be fulfilled first. Then, after having chosen a proper CAM, having set the parameters and after connecting the in- and output, we now
create a C++ project using the menu:
Dynamic Configuration Visual C++ Prototype
•
•
•
DTMF dialler
Variable tone generator
FPAA playing a children song
V. EXAMPLE OF A DYNAMICALLY RECONFIGURATING PROGRAMME
Variable tone generator
This configuration was programmed using the
AnadigmDesigner2 software and then a Visual C++
Prototype named Oscillator was created.
Choose a CAM of type OscillatorSine and set the
parameters to:
ClockA: 31.3725 kHz
Oscillator Frequency: 0.360 kHz
Peak Amplitude: 3.2 V
Fig. 7: Creating an Visual C++ Prototype
The AnadigmDesigner2 now creates all the classes
and subclasses necessary for the dynamic configuration. These subclasses have to be inserted into the
program code of the Visual C++ project. After
compilation, first the Primary Configuration Data
Fig. 9: Oscillator
The AnadigmDesigner2 has created the subclasses
for a dynamic configuration. For varying the oscillator frequency only the routines ExecuteReconfig()
(for transmission of the reconfiguration data) and
setOscillatorSine(double Fo, double A) (for varying
frequency and amplitude) are of interest.
{
CDialog::OnInitDialog();
// Setup application icon
SetIcon(m_hIcon, TRUE);
SetIcon(m_hIcon, FALSE);
// Add the "About..." menu item
ConfigureAboutMenu();
// Initialize the sample slider
m_sampleMin = 0.36;
m_sampleMax = 1.0;
m_sampleValue = 0.36;
m_sampleSlider.SetRange(0, 100);
// Initial update of sample controls
UpdateSampleControls();
return TRUE;
}
Please remark, that you have to define the project
aktive, by marking it with a hook in front of the
name.
Fig. 10: Visual C++ Project Oscillator [1]
Next, we have to define the characteristics for the
push bar in subroutine UpdateSampleControls().
This can be done easily by means of setOscillatorSine and ExecuteReconfig. Changes are represented in blue, see [8].
void OscillatorDlg::UpdateSampleControls()
{
// Map the actual sample value to the range
[0, 100] for the slider
int percent = (int) (100.0 *
(m_sampleValue - m_sampleMin) /
(m_sampleMax - m_sampleMin));
// Update the slider position
m_sampleSlider.SetPos(percent);
m_sampleSlider.Invalidate();
// Format the text for the edit control
CString value;
value.Format("%.2f kHz", m_sampleValue);
// Update the edit control text
m_sampleEdit.SetWindowText(value);
m_FPAA1.OscillatorSine1.setOscillatorSine
(m_sampleValue, 3.2);
m_FPAA1.ExecuteReconfig();
}
Using the instruction:
setOscillatorSine(m_sampleValue, 3.2) we set the
frequency of the oscillator, depending on the position of the bar. Amplitude is kept constant at 3.2 V.
Instruction ExecuteReconfig will send reconfiguration data to the evaluation board
Next we open an OscillortDlg.cpp file and define
the boundaries for the sample slider in the OnInitDialog().
Minimum was set to 0.36 kHz and maximum was
set to 1 kHz.
BOOL OscillatorDlg::OnInitDialog()
Fig. 11: Oscillator with variable frequency
Pushing button Download transmits Primary Configuration Data to the board. Now, the frequency
changes depending on the position of the sample
slider. The current frequency is shown in the text
field in the back.
You can download the example from address [8].
VI. CONCLUSION
The technology of the Field Programmable Analogue
Arrays offers attractive and universal functions. FPAAs
can be used in many different applications. But don’t
underestimate the time for training on the subject. Only
a few helpful information was provided by the producer
and the programming procedure partly followed the
crucial path of trial and error. Detailed knowledge on
the relationship of hard- and software would be helpful
for the future and could decrease the developing times
by far.
VII. ACKNOWLEDGMENT
Special thanks to Peter Dückert, Hilmar Endres and
Jochen Reuter for their kind support.
VIII. REFERENCES
[1] Eckstein, K.: Dynamische Programmierung analoger Schaltungen am Beispiel des Field Programmable
Analog Arrays AN221E04,
FH Würzburg-Schweinfurt, Diplomarbeit 2005.
[2] Reuter, J.: Der Entwurf und Aufbau spezieller analoger Filter mit programmierbaren Analog Arrays, FH
Würzburg-Schweinfurt, Diplomarbeit 2004.
[3] Möhringer, P.: Implementierung spezieller Entzerrerfilter auf FPAA, 2. Symposium der Fachhochschulen
Würzburg-Schweinfurt & Hochschule Bremen,
Schweinfurt 28.9.2004, Tagungsb. S. 57-74.
[4] Möhringer, P.: Implementation of Specific Equalising Filters using Field Programmable Analogue Arrays, Proceedings of 21st International Scientific Conference "Science for Practice", 06./07. Mai 2004, Polytechnik Engineering College Subotica, (Serbia and
Montenegro) page 71-77, COBISS.SR-ID 198996487,
www.fh-sw.de/.../fpaa-subotica.pdf.
[5] Wangenheim, L. von: Aktive Filter in RC- und SCTechnik. Hüthig Verlag, Heidelberg 1991.
[6] Anadigm AN121E04 / AN221E04 Field Programmable Analog Arrays – User Manual,
www.anadigm.com/_doc/UM021200-U007.pdf.
[7] Application Note 201 Dynamically Reconfiguration the AN220E04 FPAA,
www.anadigm.com/_doc/AP020800-U201.pdf.
[8] Eckstein, K., Möhringer, P.: Dynamically Reconfiguring of the Field Programmable Analogue Array
AN221E04,
www.fh-sw.de/sw/fachb/et/pp/vuv.html.