Micro-Cap v7.1.6 / RM

Component lists

Circuits can be constructed from the exact values required to fit the specification exactly, or they can be constructed from nearest-fit values obtained from standard lists. The lists are kept in ASCII text files that use the extensions CAP for capacitors, IND for inductors (for passive filters), and RES for resistors. The format of these files is as follows:

TOLERANCE <tolerance>[%]

DIGITS <digit 1> <digit 2>

...

<digit n>

MULTIPLIERS <multiplier 1> <multiplier 2>

...

<multiplier m>

ADD <value 1> <value 2>

...

<value p>

REMOVE <value 1> <value 2>

...

<value q>

The <tolerance> value is used when setting up the model statement for the components and affects only Monte Carlo analysis.

The program creates a list of acceptable values by forming all possible products of digits and multipliers, then adding any values found under the ADD keyword, and removing any values found under the REMOVE keyword.

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For example:

TOLERANCE 1%

DIGITS 10 50 80

MULTIPLIERS 1 10 100

ADD 26 135

REMOVE 8000

In this example the program would first compile a tentative list from the DIGITS and MULTIPLIERS groups containing these elements:

10, 50, 80, 100, 500, 800, 1000, 5000, 8000

The program would then add the values 26 and 135 and remove the 8000 value to produce the final list:

10, 26, 50, 80, 100, 135, 500, 800, 1000, 5000

The list is constructed in this way to make specification of standard component values easier. Standard values frequently are created from a small list of values, multiplied by various powers of ten. There are often exceptions, usually at the high and low ends. DIGITS and MULTIPLIER keep the list specification concise, while ADD and REMOVE help with the exceptions. All keyword items are optional, so you could create a list using only the ADD elements.

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Filter support files

The filter design program uses a file called FILTER.BIN, which is resident on the same directory as the MC7.EXE program file. It must not be removed, for it contains the generic circuit stages for each of the different circuit implementations used to build complete filter circuits. The filter program will be able to do only the mathematical portion of the design if this file is missing. That is, the program will not be able to create actual filter circuits without FILTER.BIN.

MC7 also saves your last used settings from the dialog box in the ACTIVE.FLT file. These settings can be restored to the original default settings by clicking on the Default button at the bottom of the dialog box.

When you press OK, the program creates a circuit to implement the specified filter. It names it CIRCUIT2. Each subsequent circuit becomes CIRCUIT3, then CIRCUIT4, and so on. The circuits can be renamed when they are saved to disk.

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Filter specification: mode 1

The active filter program uses two modes to define filter specifications, Mode 1, and Mode 2. Mode 1 includes the following:

Low Pass Filters:

Low pass filter specs are defined relative to the figure below:

Figure 12-5 Low pass filter specifications

Passband Gain

This is the low frequency gain in dB.

Passband Ripple (R)

This is the variation in gain (in dB) across the passband.

Stopband Attenuation (A)

This is the maximum gain in dB in the passband minus the maximum gain in dB at the stopband. Attenuation is a positive number.

Passband Frequency (Fc)

Below Fc the gain is equal to the passband gain +- ripple.

Stopband Frequency (Fs)

Above Fs the gain is less than or equal to the passband gain +- ripple less the stopband attenuation.

For Chebyshev and elliptic filters the passband gain varies with the order of the filter as follows:

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Butterworth and inverse-Chebyshev passband gain varies as follows:

Inverse-Chebyshev filters meet the passband spec with margin and meet the stopband spec exactly, with no margin. Ideal realizations of the other filters do just the opposite. They meet the stopband spec with margin and meet the passband specs exactly, with no margin.

Figure 12-6 High pass filter specifications

High Pass Filters:

High pass filter specs are very similar to their low pass cousins and are defined relative to Figure 12-6.

Passband Gain

This is the high frequency gain in dB.

Passband Ripple (R)

This is the variation in gain (in dB) across the passband.

Stopband Attenuation (A)

This is the maximum gain in dB in the passband minus the maximum gain in dB at the stopband. Attenuation is a positive number.

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Passband Frequency (Fc)

Above Fc the gain is equal to the passband gain +- ripple.

Stopband Frequency (Fs)

Below Fs the gain is less than or equal to the passband gain +- ripple less the stopband attenuation.

For Chebyshev and elliptic filters the passband gain varies as follows:

Butterworth and inverse-Chebyshev passband gain varies as follows:

Figure 12-7 Bandpass filter specifications

Inverse-Chebyshev filters meet the passband spec with margin and meet the stopband spec exactly, with no margin. Ideal realizations of the other filters do just the opposite. They meet the stopband spec with margin and meet the passband specs exactly, with no margin.

Bandpass Filters:

Bandpass filter specs are defined relative to Figure 12-7

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Passband Gain

This is the maximum gain in dB in the passband.

Passband Ripple (R)

This is the variation in gain in dB across the passband.

Stopband Attenuation (A)

This is the maximum gain in dB in the passband minus the maximum gain in dB at the stopband. Attenuation is a positive number.

Center Frequency (Fc)

This is the center frequency of the passband.

Passband (PB)

This is the band of frequencies where the filter gain is equal to the passband gain (plus or minus the ripple).

Stopband (SB)

This is the band of frequencies which includes the PB plus the two transition regions above and below the passband. It is also the frequency where the filter gain is larger than the total of passband gain + attenuation (plus or minus the ripple).

For Chebyshev and elliptic filters the passband gain varies with the order of the filter as follows:

Butterworth and inverse-Chebyshev passband gain varies as follows:

Inverse-Chebyshev filters meet the passband spec with margin and meet the stopband spec exactly, with no margin. Ideal realizations of the other filters do just the opposite. They meet the stopband spec with margin and meet the passband specs exactly, with no margin.

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Notch Filters:

Notch or band reject filter specs are defined relative to Figure 12-8:

Figure 12-8 Notch filter specifications

Passband Gain

This is the maximum gain in dB outside the passband.

Passband Ripple (R)

This is the variation in gain (in dB) outside the passband.

Stopband Attenuation (A)

This is the maximum gain in dB outside the passband minus the maximum gain in dB in the stopband. Attenuation is a positive number.

Center Frequency (Fc)

This is the center frequency of the stopband.

Passband (PB)

This is the band of frequencies which includes the SB plus the two transition regions above and below the stopband.

Stopband (SB)

This is the band of frequencies where the filter gain is smaller than the total of passband gain minus stopband attenuation (A), plus or minus the ripple.

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For Chebyshev and elliptic filters the passband gain varies with the order of the filter as follows:

Butterworth and inverse-Chebyshev passband gain varies as follows:

Inverse-Chebyshev filters meet the passband spec with margin and meet the stopband spec exactly, with no margin. Ideal realizations of the other filters do just the opposite. They meet the stopband spec with margin and meet the passband specs exactly, with no margin.

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Filter specification: mode 2

Mode 2 formats allow direct specification of the filter order. Its formats are as follows:

Low (High) Pass Filters:

Gain

This is the low (high) frequency gain in dB.

Passband Frequency

This is the frequency below (above) which the gain is equal to Gain.

Ripple

This is the variation in gain (in dB) across the passband.

Order

This is the filter order.

Bandpass and Notch Filters:

Gain

This is the center frequency gain in dB (bandpass) or the low / high frequency gain in dB (notch).

Center Frequency

This is the frequency at which the maximum (bandpass) or minimum (notch) gain is achieved.

Ripple

This is the variation in gain in dB across the passband (bandpass) or outside the passband (notch).

Order

This is the filter order.

Q

This is the filter Q factor. Q is a measure of the resonance near the center frequency.

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