Frequency Devices ASC-50 User manual

25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] • Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
ASC-50
OPERATION MANUAL
September 2001

TABLE OF CONTENTS
1. ASC-50 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Available types of filter transfer functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Description of front panel controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Using the ASC-50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Definition of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
6. Sample rate control explanation and Chart 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Operational Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. ASC-50 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
9. Power and fuzing instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
10. Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
11. IIR transfer function curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
12. FIR transfer function curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] • Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
I

The ASC-50 is a self-contained signal conditioning filter/amplifier instrument that combines Analog and Digital
Signal Processing (DSP) capabilities hile providing conventional analog signal input and output. Analog and
DSP functions are available ithout the need for computer programming hile familiar analog instrument
operation is maintained. Data entry is accomplished via a “soft front panel” and a t o line Liquid Crystal
Display (LCD) that prompts the user to select among various menu choices.
Features
Wide variety of filter types, functions and frequencies
Precise, stable filter performance
Adjustable gain and attenuation
DC offset control
Choice of single or differential inputs
Special DSP bypass
Analog and DSP clip indicators
Filter performance display
Filter Types
Lo -pass (LP)
High-pass (HP)
Band-pass (BP)
Band-reject (BR)
Filter Functions
Butter orth (Buttr)
Chebyshev (Cheby)
Elliptic-60dB (Ell60)
Elliptic-80dB (Ell80)
FIR-40dB (FIR 0)
FIR-60dB (FIR60)
FIR-80dB (FIR80)
Gain Control
PRE - Analog pre-gain range 0 to +36dB in 6dB steps
POST - Digital post-gain range -48dB to +42dB in 6dB steps
DC Offset Control - Input DC offset range
±5 Volts
Over-Range Indication
Analog saturation, clipping detection (←← CLIP)
Digital saturation, clipping detection (CLIP →→)
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] • Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
1

Available Low-Pass, High-Pass Transfer Functions
ANALOG
Butter orth 4,6,8,10 Pole
Chebychev (0.1dB Ripple) 4,6,8,10 Pole
Elliptic-60 dB (0.1dB Ripple) 4,6,8,10 Pole
Elliptic-80 dB (0.1dB Ripple) 4,6,8,10 Pole
DIGITAL
FIR-40 dB
FIR-60 dB
FIR-80 dB
Band-Pass, Band-Reject Transfer Functions
ANALOG
Butter orth 3,4 Pole-Pair Q = 2,5,10,20
Chebychev 3,4 Pole-Pair Q = 2,5,10,20
Elliptic-60 dB (0.1dB Ripple) 3,4 Pole-Pair Q = 2,5,10,20
Elliptic-80 dB (0.1dB Ripple) 3,4 Pole-Pair Q = 2,5,10,20
DIGITAL
FIR-40 dB BW1,BW2,BW3,BW4
FIR-60 dB BW1,BW2,BW3,BW4
FIR-80 dB BW1,BW2,BW3,BW4
LOCATION OF FRONT PANEL CONTROLS AND TERMINATIONS
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] • Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
2
ASC50
MODEENTERBYP
I
N
O
U
T
RESET

Power-On/Off
A t o-position toggle s itch located on the rear panel turns the AC po er on and off. Upon po er-on, the front
panel ill display MODE 1 of the set-up present at the time po er as turned off.
A. Mode Key
Many more functions are controlled than could be displayed on one screen. Four modes of operation are
utilized. Each press of the MODE key displays a different mode (1 through 4). Four consecutive presses of
the MODE key ill return the display to the initial mode.
B. Enter Key
In order to load the filter chosen via the arro keys, it is necessary to press the Enter key. Until this is done
the present filter is still operating. This allo s the operator to spool through the available choices before making
a selection. When in MODE 1, to arn the user that a ne filter selection has not yet been made operational,
the Warning: <ENT> flashes. It is extinguished by pressing the ENTER key hich loads the selected filter.
C. Arrow Keys
Four arrow (←←, →→, ↑↑, ↓↓) keypads are available to highlight fields and make selections. The left ←←and right
→→arrows allo movement ithin fields and are used to select the field to be modified. Continuous looping
through all the fields ill occur as the left ←←or right →→arrow key is repeatedly pressed. The up ↑↑and down
↓↓arrows cycle bet een the various choices available in each field. Changes that require use of the ENTER
key are indicated by the flashing <ENT> symbol (MODE 1 only).
D. Reset Key
During the filter selection process and before pressing Enter or hile the arning <ENT> flashes, the user can
return the display to the current active filter mode by pressing RESET.
E. Bypass Key
The internal DSP filter can be bypassed by pressing the BYP key. This ill bypass the DSP filter, but not the
input anti-alias (AA) and output reconstruction (RC) filters. The BYP key toggles bet een the active and
bypass modes (denoted ACT and BYP on the display) and al ays returns the display to MODE 1. This permits
the operator to monitor the effects of the DSP filter.
F. Input Connectors
T o shielded, female BNC input (+IN and -IN) connectors are present on the front panel. An input signal
connected to the +IN provides single-ended input. To operate in the differential input mode, differential input
signals must be connected to the +IN and -IN connectors. The -IN connector is only used for the differential
input-operating mode.
G. Output Connector
One shielded female BNC output connector is present on the front panel.
H. LCD Display
A t o-line display indicates the setup choices available as ell as providing the user selected characteristics.
Fields that are controllable are presented to the display for vie ing (a flashing cursor ithin a field indicates
the specific parameter that can be modified by utilizing the arro keys). Selected performance characteristics
are also identified. A Menu Options chart is included (see Attachment 1) to indicate ho selections are
made ithin modes and fields. . User choices are made via the arrow (←←,, →→,, ↑↑,, ↓↓) and Enter Keys.
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
3

USING THE ASC-50
User Interface
User entry is accomplished by means of a “soft front panel” ith the user entry prompted by the display.
Left ←←and Right →→Arrows - place the blinking cursor on the function that is to be changed.
Up ↑↑and Down ↓↓Arrows - make changes to the current setup.
<ENT> - In MODE 1 a blinking <ENT> on the display reminds the user that ne functions are not implemented
until the ENTER button is pressed.
MODE - selects hich menu is displayed. MODE makes no changes to the current setup. By repeatedly
pressing MODE the entire setup can be revie ed ithout making any changes.
ENTER - implements the selected setup.
BYP - provides a special DSP bypass operation, its use is signaled on the display.
RESET - allo s the previous setup to be restored.
Flashing Cursor
AFlashing Cursor indicates hich field is a aiting update.
DISPLAY MODES
Three display modes register the complete range of operational choices; the fourth mode provides filter
characteristics. Pressing the MODE key a maximum of three times ill display the modes in succession. The
fourth time MODE is pressed the original display is returned.
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
4

Mode 1
Field 1 - Filter type
A. LP (Lo -pass)
B. HP (High-pass)
C. BP (Band-pass)
D. BR (Band-reject)
Field 2 - Filter function
A. Buttr (Butter orth)
B. Cheby (Chebyshev)
C. Ell60 (Elliptic-60dB)
D. Ell80 (Elliptic-80dB)
E. FIR40 (Finite Impulse Response 40dB)
F. FIR60 (Finite Impulse Response 60dB)
G. FIR80 (Finite Impulse Response 80dB)
Field 3 - Number of Poles
(Does not apply for FIR filters
A. 4P (4 Pole)
B. 6P (6 Pole)
C. 8P (8 Pole)
D. 10P (10 Pole)
E. 3PP (3 Pole Pair)
F. 4PP (4 Pole Pair)
Mode 2
Field 1 - Analog Pre-gain Control
A. Pre-gain ( 0dB to +36dB)
Mode 3
Field 1 - Single / Differential Input Control
A. SNG (Single Ended Input)
B. DIF (Differential Mode Input)
Mode
Field 1 - Filter Performance,
Shape Factor/Transition Band
A. Shape Factor - Shape Factor Ratio
B. Trans BW-Transition Band idth (Hz)
C. Pass BW-Pass-band Band idth (Hz)
D. Stop BW-Stop-band band idth (Hz)
E. Warning - 1, 2, 3
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
5
Field - Q/Band idth
A. Q2 (Q=2) Does not apply to FIR40, FIR60,
FIR80
B. Q5 (Q=5) Does not apply to FIR40, FIR60,
FIR80
C. Q10 (Q=10) Does not apply to FIR40, FIR60,
FIR80
D. Q20 (Q=20) Does not apply to FIR40, FIR60,
FIR80
E. BW1 (FIR BW #1) Does not apply to Buttr,
Cheby, Ell60, Ell80
F. BW2 (FIR BW #2) Does not apply to Buttr,
Cheby, Ell60, Ell80
G. BW3 (FIR BW #3) Does not apply to Buttr,
Cheby, Ell60, Ell80
H. BW4 (FIR BW #4) Does not apply to Buttr,
Cheby, Ell60, Ell80
Field 5 – Active/Bypass
A. Active mode (ACT)
B. DSP Bypass mode (BYP)
Field 6 – Corner Frequency
A. 0.10 Hz - 0.99 Hz (0.01 Hz Steps)
B. 1 Hz - 9.9 Hz (0.1 Hz Steps)
C. 10 Hz - 99 Hz (1 Hz Steps)
D. 100 Hz - 990 Hz (10 Hz Steps)
E. 1,000 Hz - 9,900 Hz (100 Hz Steps)
F. 10,000 Hz - 30,000 Hz (1000 Hz Steps)
Field 2 - DSP Post-gain Control
A. Post-gain (-48dB to +42dB)
Field 2 - Input DC Offset Control, relative DC
offset
A. ±5V range in ⊃0.15mV steps
Field 2 – Stop-band Band idth
A. BW (Hz)

Filter performance characteristics presented to the display are not available for change but rather indicate
relative performance of the various filters (See Attachment 2 for plots of the available filter transfer functions).
Shape Factor (SF)
Used for analog filters to indicate the ratio of corner frequency of the filter to attenuation floor frequency. In the
case of Butter orth (Buttr) and Chebychev (Cheby) filters an attenuation level of 80dB is assumed. Band-pass
(BP) and Band-reject (BR) filters exhibit the same attenuation slope on both the upper and lo er sides of the
response (symmetric).
Transition Bandwidth (Trans BW)
Lo -pass (LP) and high-pass (HP) digital filters are labeled ith a band idth (Hz) that expresses the difference
bet een the attenuation floor frequency and the upper (LP) or lo er (HP) limit of the pass-band frequency.
Pass-band Bandwidth (Pass BW)
Band-pass (BP) and Band-reject (BR) digital FIR filters are labeled ith a band idth (Hz) that expresses the
difference bet een the t o pass-band frequencies. The band-pass (BP) passes frequencies over the range
(Fc ± BW/2). The band-reject (BR) passes frequencies outside the range (Fc ± BW/2).
Stop-band Bandwidth (Stop BW)
Band-pass (BP) and band-reject (BR) digital FIR filters are labeled ith a band idth (Hz) that expresses the
difference bet een the t o stop-band frequencies. The band-pass (BP) filter rejects frequencies outside of the
range (Fc ± BW/2). The band-reject (BR) rejects frequencies over the range (Fc ± BW/2).
WARNING MESSAGES
Warning Messages indicate that a filter is operating outside of normal limits.
Warning 1 - HP FIR (Attenuation @ DC)
This message is displayed hen the selected FIR high-pass filter is unable to achieve the desired level of
attenuation at a frequency of 0 Hz (DC).
Warning 2 - BP FIR (Attenuation @ DC)
This message is displayed hen the selected FIR band-pass filter is unable to achieve the desired level of
attenuation at a frequency of 0 Hz (DC).
Warning 3 - BR FIR (Attenuation @ DC)
This message is displayed hen the selected FIR band-reject filter is unable to achieve the desired level of
attenuation at a frequency of 0 Hz (DC).
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
6

Sampling Rate Control
The maximum band idth of any DSP system is limited to less than one-half of the sampling frequency. In the
case of the ASC-50 the maximum band idth is one-quarter of the sampling frequency. In order to provide the
highest performance from the available band idth the ASC-50 provides an automatic-sampling rate selection
control. A sampling frequency bet een 36Hz and 150kHz is chosen depending on the filter type, function and
frequency (See CHART 1 belo ).
Filter Filter Corner Sample System
Function Type Frequency Frequency BW
LP,HP Analog/Digital Fc < 0.735 Hz 36.7 Hz 9 Hz
BP,BR Analog/Digital Fc < 1.47 Hz 36.7 Hz 9 Hz
LP,HP Analog/Digital 1.47 Hz > Fc >= 0.735 Hz 73.5 Hz 18 Hz
BP,BR Analog/Digital 2.94 Hz > Fc >= 1.47 Hz 73.5 Hz 18 Hz
LP,HP Analog/Digital 2.94 Hz > Fc >= 1.47 Hz 147.1 Hz 36 Hz
BP,BR Analog/Digital 5.88 Hz > Fc >= 2.94 Hz 147.1 Hz 36 Hz
LP,HP Analog/Digital 5.88 Hz > Fc >= 2.94 Hz 294.1 Hz 73.5 Hz
BP,BR Analog/Digital 11.76 Hz > Fc >= 5.88 Hz 294.1 Hz 73.5 Hz
LP,HP Analog/Digital 11.76 Hz > Fc >= 5.88 Hz 588.3 Hz 147 Hz
BP,BR Analog/Digital 23.53 Hz > Fc >= 11.76 Hz 588.3 Hz 147 Hz
LP,HP Analog/Digital 23.53 Hz > Fc >= 11.76 Hz 1.17 kHz 294 Hz
BP,BR Analog/Digital 47.06 Hz > Fc >= 23.53 Hz 1.17 kHz 294 Hz
LP,HP Analog/Digital 47.06 Hz > Fc >= 23.53 Hz 2.35 kHz 588 Hz
BP,BR Analog/Digital 94.12 Hz > Fc >= 47.06 Hz 2.35 kHz 588 Hz
LP,HP Analog/Digital 94.12 Hz > Fc > = 47.06 Hz 4.71 kHz 1.17 kHz
BP,BR Analog/Digital 188.25 Hz > Fc >= 94.12 Hz 4.71 kHz 1.17 kHz
LP,HP Analog/Digital 188.25 Hz > Fc >=94.12 Hz 9.41 kHz 2.35 kHz
BP,BR Analog/Digital 376.50 Hz > Fc >= 188.25 Hz 9.41 kHz 2.35 kHz
LP,HP Analog/Digital 376.50 Hz > Fc >= 188.25 Hz 18.8 kHz 4.71 kHz
BP,BR Analog/Digital 753.00 Hz > Fc >= 376.50 Hz 18.8 kHz 4.71 kHz
LP,HP Analog 753.00 Hz > Fc>= 376.50 Hz 37.6 kHz 9.41 kHz
LP,HP Digital 1.506 kHz > Fc >= 376.50 Hz 37.6 kHz 9.41 kHz
BP,BR Analog 1.506 kHz > Fc >= 753.00 Hz 37.6 kHz 9.41 kHz
BP,BR Digital 3.012 kHz > Fc>= 753.00 Hz 37.6 kHz 9.41 kHz
LP,HP Analog 1.506 kHz > Fc >= 753.00 Hz 75.3 kHz 18.8 kHz
LP,HP Digital 6.024 kHz > Fc >= 1.506 kHz 75.3 kHz 18.8 kHz
BP,BR Analog 3.012 kHz > Fc >= 1.506 kHz 75.3 kHz 18.8 kHz
BP,BR Digital 12.048 kHz > Fc >= 3.012 kHz 75.3 kHz 18.8 kHz
LP,HP Analog 30.000 kHz > Fc >= 1.506 kHz 150.6 kHz 37.6 kHz
LP,HP Digital 30.000 kHz > Fc >= 6.024 kHz 150.6 kHz 37.6 kHz
BP,BR Analog 30.000 kHz > Fc >= 3.012 kHz 150.6 kHz 37.6 kHz
BP,BR Digital 30.000 kHz > Fc >= 12.048 kHz 150.6 kHz 37.6 kHz
CHART 1
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
7

OPERATIONAL CONSIDERATIONS
Anti Alias and Reconstruction Filters
The automatic sample control is transparent to the user and operates the internal input anti-alias (AA) and
output reconstruction (RC) filters. These filters, operating in cascade, determine the system band idth and
phase characteristics.
The system band idth (amplitude response) is al ays limited to one-quarter of the sampling frequency in use.
CHART 1 (above) sho s the sample rate and system band idth for the available filter configurations. For lo -
pass (LP) and band-pass (BP) filters this is of little consequence because the cutoff frequency is internally
programmed to be ithin the system band idth. Ho ever, the high frequency amplitude response of high-pass
and band-reject filters is limited to the system band idth.
The phase response of the AA and RC filters is al ays added to the filter function that is selected via the front
panel. This effect is more pronounced on analog filter transfer functions than on the digital (FIR) filter transfer
functions and hen the filter selected is programmed to a frequency close to the sample rate. The delay, in
digital (FIR) transfer functions, hich appears as linear phase shift, is generally large enough that the phase
contributed by the AA and RC filters is not significant. Figure 1 illustrates the effects of this additional phase
on typical Butter orth lo -pass filters ith corner frequencies of 10% and 80% of system band idth.
FIGURE 1
25 Locust St, Haverhill, Massachusetts 01830 • Tel: [phone] • FAX: [phone]
e-mail: [e-mail] •Web Address: http://www.freqdev.com
ASC-50
Operation
Manual
8
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Normalized Frequency (system band idth)
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
Phase (deg)
6 Pole Butter orth Lo pass Phase response
fc = 10% of system band idth
/o aaf & reconstruction filter
/ aaf & reconstruction filter
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Normalized Frequency (system band idth)
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
Phase (deg)
6 Pole Butter orth Lo pass Phase response
fc = 80% of system band idth
/o aaf & reconstruction filter
/ aaf & reconstruction filter
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Normalized Frequency (system band idth)
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
Amplitude (dB)
Anti-Alias & Reconstruction Filter
Frequency Response
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Normalized Frequency (system band idth)
-1400
-1200
-1000
-800
-600
-400
-200
0
Phase (deg)
Anti-Alias & Reconstruction Filter
Phase Response