Band-rejection filter of the switched capacitor type

• US 4,518,935 A
• Filed: 09/26/1983
• Issued: 05/21/1985
• Est. Priority Date: 07/12/1983
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: van Roermund, Arthur H. M.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/535,497
• Time in Patent Office: 603 Days
• Field of Search: 333/173, 333/172, 333/174, 333/175, 333/167, 328/151, 328/167, 328/127, 330/109, 307/352, 307/353, 307/520-524, 364/724
• US Class Current: 333/173
• CPC Class Codes: H03H 19/004 Switched capacitor networks

Abstract

Band-rejection filter of the switched capacitor type in which at least one unwanted frequency component present in an information signal must be suppressed. To that end this filter comprises and adding circuit 4 to which the information signal is applied via a switching device 3 and a feedback signal via a switching device 5. Both switching devices are controlled by a first control signal consisting of a sequence of control signal periods of a duration T_s which are each divided into a tracking phase and into an interrupt phase. During the tracking phase the signal can pass uninterruptedly through the switching device, while during the interrupt phase signals are not allowed to pass. The output of adding circuit 4 is coupled inter alia via a switching device 8 to the input of a bandpass filter 9 whose passband at least coincides with the unwanted frequency component. The switching device 8 is controlled by a second control signal which is also formed by a sequence of control signal periods of a duration T_s and which are each divided into a tracking and an interrupt phase.

In order to realize an adequate suppression of the unwanted frequency component the instants at which the tracking phases in the first control signal and the tracking phases in the second control signal end are mutually phase-shifted over a fixed distance.

Claims

1. A band-rejection filter of the switched capacitor type for suppressing at least one unwanted frequency component present in an analogue information signal, comprising:

(a) a filter input for receiving the analogue information signal and a filter output;

(b) combining means whose output is coupled to the filter output;

(c) first switching means for applying the information signal and a feedback signal to the combining means and which are controlled by a first control signal;

(d) a bandpass filter of the switched capacitor type the passband of which comprises at least the unwanted frequency component and which produces the said feedback signal;

(e) second switching means for coupling the input of the bandpass filter to the filter output and which are controlled by a second control signal;

(f) a control signal generator for producing the first and second control signals, each consisting of a sequence of control signal periods of a duration T_s and occurring at a frequency f_s (T_s =1/f_s), each control signal period being partitioned into a tracking phase and an interrupt phase, the instants at which the tracking phases in the first and second control signals end evidencing a fixed phase shift which is unequal to zero and less than half a control signal period.