SSI32F8030 Datasheet, PDF (2/10 Pages) List of Unclassifed Manufacturers – Programmable Electronic Filter

SSI 32F8030
Programmable
Electronic Filter
FUNCTIONAL DESCRIPTION
The SSI 32F8030, a high performance programmable
electronic filter, provides a low pass 0.05° Equiripple-
type linear phase seven pole filter with matched normal
and differentiated outputs. The device has been opti-
mized for usage with several Silicon Systems prod-
ucts, including the SSI 32D4661 Time Base Generator,
the SSI 32P54x family of Pulse Detectors, and the SSI
32P4720 Combo device (Data Separator and Pulse
Detector).
CUTOFF FREQUENCY PROGRAMMING
The SSI 32F8030 programmable electronic filter can
be set to a filter cutoff frequency from 250 kHz to 2.5
MHz (with no boost).
Cutoff frequency programming can be established
using either a current source fed into the IFP pin, whose
output current is proportional to the SSI 32F8030
output reference voltage VR, or by means of an exter-
nal resistor tied from the output voltage reference pin
VR to pin VFP. The former method is optimized using
the SSI 32D4661 Time Base Generator, since the
current source into pin IFP is available at the DAC F
output of the 32D4661. Furthermore, the voltage
reference input is supplied to pin VR3 of the 32D4661
by the reference voltage VR from the VR pin of the
32F8030. This reference voltage is an internally gen-
erated bandgap reference, which typically varies less
than 1 % over voltage supply and temperature varia-
tion. (For the calculations below IVFP = current into IFP
or VFP pins).
The cutoff frequency, determined by the -3dB point
relative to a very low frequency value (< 10kHz), is
related to the current IVFP injected into pin IFP by the
formula
Fc (ideal, in MHz) = 3.125•IFP = 3.125•IVFP•2.2/VR,
where IFP and IVFP are in mA, 0.08<IFP<0.8 mA, and
VR is in volts.
If a current source is used to inject current into pin IFP,
pin VFP should be left open.
If the 32F8030 cutoff frequency is set using voltage VR
to bias up a resistor tied to pin VFP, the cutoff frequency
is related to the resistor value by the formula
Fc (ideal, in MHz) = 3.125•IFP = 3.125•2.2/(3•Rx)
where Rx is in kΩ, & 0.917 kΩ <Rx<9.17 kΩ.
If pin VFP is used to program cutoff frequency, pin IFP
should be left open.
SLIMMER HIGH FREQUENCY BOOST
PROGRAMMING
The amplitude of the output signal at frequencies near
the cutoff frequency can be increased using this fea-
ture. Applying an external voltage to pin VBP which is
proportional to reference output voltage VR (provided
by the VR pin) will set the amount of boost. A fixed
amount of boost can be set by an external resistor
divider network connected from pin VBP to pins VR and
GND. No boost is applied if pin FBST, frequency boost
enable, is at a low logic level.
The amount of boost FB at the cutoff frequency Fc is
related to the voltage VBP by the formula
FB (ideal, in dB) = 20 log10[1.884(VBP/VR)+1], where
0<VBP<VR.
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