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LPF_RaisedCos (Lowpass Filter, Raised-Cosine)

Symbol

Available in ADS and RFDE

Parameters

Name

Description

Units

Default

Alpha

Rolloff factor defining filter excess bandwidth, 0 ≤ Alpha ≤ 1

None

0.35

SymbolRate

Digital symbol rate defining filter bandwidth

kHz

24.3

DelaySymbols

Number of symbols delayed by filter

None

5

Exponent

Exponent factor ( 0 ≤ Exponent ≤ 1 ), to provide for Root Raised-Cosine filter

None

0.5

DutyCycle

Pulse duty cycle in percent, used for sinc(x) correction

None

0

SincE

Flag to include the Exponent factor on the sinc(x) correction: yes or no

None

no

Gain

Gain factor

None

1.0

Zout

Output impedance

Ohm

50

WindowType

Window type applied to impulse response: 0=None, 1=Hann, 2=Hamming

None

0

ImpMaxFreq

Maximum frequency to consider when calculating impulse response

 

 

ImpDeltaFreq

Frequency sample spacing when calculating impulse response

 

 

ImpMaxPts

Maximum number of points in impulse response

None

None

Other

output string to netlist

None

None

Range of Usage

0 ≤ Alpha ≤ 1
DelaySymbols ≥ 1
0 ≤ Exponent ≤ 1
0 ≤ DutyCycle ≤ 100

Notes/Equations
  1. Refer to Filter Categories.
  2. For information on lowpass filter behavior at DC, refer to Lowpass Filter Behavior at DC.
  3. This filter is unidirectional; input impedance is infinite; output impedance is specified by Zout.
  4. Voltage gain is described by the following function.

    where:

    Gfilt

    = 1.0 for frequency ≤ 0.5 × (1 − Alpha ) × SymbolRate

     

     

    = 0.0 for frequency ≥ 0.5 × (1 + Alpha ) × SymbolRate

     

     

    = [0.5 × (1 − sin[π × ( frequencySymbolRate /2)/

     

    Gcomp

    = 1.0

    if DutyCycle =0

     

    = [0.01 × DutyCycle  × sinc(x)]Exponent

    if SincE = YES

     

    = [0.01 × DutyCycle  × sinc(x)]

    if SincE = NO

    sinc(x)

    = sin(x)/x

     

    x

    = 0.01 × DutyCycle × π × frequency / SymbolRate

     

  5. While Exponent can be any value, the standard value is 1.0 for the ideal raised-cosine filter response or 0.5 to simulate the root raised-cosine filter response when present at both the receiving and transmitting channels.
  6. In steady-state frequency-domain analyses, the ideal frequency-domain response described previously is used; however, this ideal response has an infinite duration impulse response that must be approximated for time-domain simulations in either transient or circuit envelope. If DelaySymbols is set too small, then the impulse response will be severely truncated and will not accurately reflect the ideal frequency response.
    A DelaySymbols value of 15 should result in saturated frequency-domain sidelobes of -75dBc or smaller. This number is approximate and represents the saturated sidelobe level at frequencies far greater than the filter's cutoff frequency. The sidelobes at, say, twice the filter's cutoff frequency have generally not saturated and will typically be higher than -75 dBc. The saturated sidelobe level may depend on whether a transient or circuit envelope simulation is performed and on the window type used. It is significantly lower than -75dBc in many cases. The accuracy of this model in transient or circuit envelope simulations can be further controlled through the ImpMaxFreq, ImpDeltaFreq, and ImpMaxPts parameters.
  7. The filter can include gain equalization to compensate for duty cycle roll-off. If DutyCycle = 0.0, then no compensation will be applied. If SincE=YES, Exponent will be applied to the gain compensation term Gcomp . The Exponent term is always present in the Gfilt term.
  8. This component has no default artwork associated with it.
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