US 5,625,317 A · Tuning method for integrated continuous-time filters

Abstract

A high-frequency integrated continuous-time filter with built-in test mode. The present invention provides the ability to easily track the cutoff frequency of the filter without the additional power and area requirements and noise sources present in prior art master/slave tuning schemes. Furthermore, the filter being tested is the actual filter that is used to process signals, unlike the prior art where a similar but separate filter or oscillator is used to tune the bias values for both circuits. Better tuning accuracy is thus obtained in the present invention. The circuit is designed to oscillate in test mode at the cutoff frequency of the filter. Oscillation is achieved by moving the poles of the filter from the left half-plane either onto the imaginary axis or into the right half-plane. The filter frequency accuracy is established by trimming the frequency of the oscillation in test mode during wafer probe or by adjusting the circuit biasing to tune the cutoff frequency in test mode during power-up or between reads in a memory system. The oscillation is disabled during normal operation of the filter.

Claims49

Dependent claims

A method for tuning a cutoff frequency of a filter having a plurality of poles in an s-plane associated with a first filter element comprising the steps of:

enabling a test mode of said filter wherein said plurality of said poles of said filter are re-positioned in a region of the right half-plane of the s-plane to achieve oscillation of said filter at said cutoff frequency, said repositioning comprising the alteration of a first value of said first filter element, said filter in said test mode having a frequency of oscillation;
tuning said filter until said frequency of osciIlation has reached a desired frequency value;
and
disabling said test mode to stop said oscillation and to permit said filter to perform filtering operations after said tuning is complete, said disabling comprising returning said plurality of poles to the left half-plane.

1 more element

A filter circuit having a built-in test mode for tuning a cutoff frequency, said filter comprising:

at least one filter section having an input and an output, said filter section filtering an input signal received on said input to provide a filtered output, said at least one filter section having a filter element with a first value;
pole shifting means coupled to said filter element, said pole shifting means enabled in said test mode, said pole shifting means altering said first value of said filter element to cause oscillation of said filter section at said cutoff frequency. by repositioning a plurality of poles of said filter section into a region of the right half-plane of the s-plane, said plurality of poles returning to the left half-plane when said pole shifting means is disabled after said tuning is complete.

A filter circuit having a test mode for tuning a cutoff frequency, said filter comprising:

at least one filter section having an input and an output, said at least one filter section having a plurality of poles associated with a first value of a filter element, said filter section filtering an input signal received on said input to provide a filtered output;
pole shifting means coupled to said filter element, said pole shifting means enabled in a test mode, said pole shifting means having a second value of opposing polarity to said first value of said filter element such that oscillation of said filter section occurs at said cutoff frequency for tuning said filter when said pole shifting means is enabled;
and
wherein said at least one filter section comprises:
first transconductance means having a first input port and first output port, said first transconductance means having a first transconductance value;
first capacitive means coupled to said first output port;
second transconductance means having a second input port and second output port, said second input port coupled to said first capacitive means, said second transconductance means having a second transconductance value;
second capacitive means coupled to said second output port;
third transconductance means having a third input and a third output, said third input coupled to said second capacitive means, said third output coupled to said second capacitive means, said third transconductance means having a third transconductance value;
fourth transconductance means having a fourth input port and a fourth output port, said fourth input port coupled to said third input port, said fourth output port coupled to said first capacitive means, said fourth transconductance means having a fourth transconductance value.

7 more elements

Dependencies are inferred from the claim text.

Tuning method for integrated continuous-time filters

Life of this patent

Tuning method for integrated continuous-time filters

Life of this patent

Abstract

Claims49