Patent US4595885A successfully refreshed from Google Patents.
US4595885A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Adjustable active filter
Assignee: Motorola Solutions Inc
•
Filing: 1984-10-01
•
Granted: 1986-06-17
•
Expires: 2004-10-01
Abstract
Abstract An adjustable active filter includes a transconductance amplifier (60) and a current source (40, 42) which may be adjusted in value. The resonant frequency of the active filter may be adjusted upwards by increasing the bias current of the transconductance amplifier using a frequency trim up network (48). The resonant frequency may be adjusted downward by decreasing the bias current using a frequency trim down network (44). The trim is preferably accomplished by shorting out zener diodes (120, 122, 124, 126, 150, 152) which control the bias current of the transconductance amplifier.
Inventors
- 👤 Yolanda Prieto
- 👤 Walter L. Davis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 16:55
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/54; H03H11/02; H03H11/04
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
146 words
An adjustable active filter, comprising: a transconductance amplifier having an input and an output and a first bias resistor; a current source for providing a controlled level of bias current to said transconductance amplifier; a feedback network coupled to said input and said output for establishing predetermined filter characteristics from said input to said output, said filter characteristics including a resonant frequency which is a function of the transconductance of said transconductance amplifier; and first current adjusting means, coupled to said transconductance amplifier, for adjusting the current provided by said current source to said transconductance amplifier, said first current adjusting means including a first resistor which may be selectively placed in parallel with said first bias resistor, whereby selectively placing said first resistor in parallel with said first bias resistor alters the transconductance of said transconductance amplifier thereby effectively adjusting said resonant frequency of said filter.
Claim 2
Dependent Claim
146 words
An adjustable active filter, comprising: a transconductance amplifier having an input and an output and a first bias resistor; a current source for providing a controlled level of bias current to said transconductance amplifier; a feedback network coupled to said input and said output for establishing predetermined filter characteristics from said input to said output, said filter characteristics including a resonant frequency which is a function of the transconductance of said transconductance amplifier; and first current adjusting means, coupled to said transconductance amplifier, for adjusting the current provided by said current source to said transconductance amplifier, said first current adjusting means including a first resistor which may be selectively placed in parallel with said first bias resistor, whereby selectively placing said first resistor in parallel with said first bias resistor alters the transconductance of said transconductance amplifier thereby effectively adjusting said resonant frequency of said filter.
Claim 3
Dependent Claim
62 words
The adjustable active filter of claim 1, further including: a second bias resistor coupled to said transconductance amplifier; and second current adjusting means, coupled to said transconductance amplifier, for adjusting the current provided by said current source to said transconductance amplifier, said second current adjusting means including a second resistor which may be selectively placed in parallel with said second bias resistor.
Claim 4
Dependent Claim
43 words
The adjustable active filter of claim 2, wherein said first current adjusting means provides for effecting an increase in bias current to said transconductance amplifier and said second current adjusting means provides for effecting a decrease in bias current to said transconductance amplifier.
Claim 5
Dependent Claim
32 words
The adjustable active filter of claim 2, wherein said first current adjusting means provides for effecting a fine current adjustment and said second current adjusting means provides for a coarse current adjustment.
Claim 6
Dependent Claim
41 words
The adjustable active filter of claim 1, further including a first zener diode in series with said first resistor and wherein said first resistor may be placed in parallel with said first bias resistor by short circuiting said first zener diode.
Claim 7
Dependent Claim
41 words
The adjustable active filter of claim 2, further including a second zener diode in series with said second resistor and wherein said second resistor may be placed in parallel with said second bias resistor by short circuiting said second zener diode.
Claim 8
Dependent Claim
49 words
The adjustable active filter of claim 1, wherein said first current adjusting means further includes a first plurality of resistors which may be selectively placed in parallel with said first bias resistor to effect a change in said bias current; said first plurality of resistors including said first resistor.
Claim 9
Dependent Claim
49 words
The adjustable active filter of claim 2, wherein said second current adjusting means further includes a second plurality of resistors which may be selectively placed in parallel with said second bias resistor to effect a change in said bias current; said second plurality of resistors including said second resistor.
Claim 10
Dependent Claim
28 words
The adjustable active filter of claim 8, wherein said second plurality of resistors includes resistors having values which provide for a modulo 2 adjustment in said resonant frequency.
References Cited (Backward Citations)
US3480835A
Cited
US4238738A
Cited
US4207538A
Cited
US4260956A
Cited
US4267519A
Cited
US4424461A
Cited
US4340868A
Cited
US4438411A
Cited
US4513254A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-06-16 | 1989-12-16 | 1990-06-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-06-16 | 1993-12-16 | 1994-06-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-06-16 | 1997-12-16 | 1998-06-17 | $7700.00 | Window Closed / Lapsed |