Multi-phase filter/DAC

A discrete time filter, for use with a sampled input signal and for producing a sampled analog output signal, comprising:

• P primary filters each coupled to receive said sampled input signal and each producing a respective sample output signal, P>1;
• M digital-to-analog converters (DACs) each having a digital input port and an analog output port and having respective analog conversion gains a.sub.m, 1<M.ltoreq.P;
• a first combination network having P input ports, each coupled to receive the output of a respective one of said primary filters, said combination network also having M output ports, each coupled to a respective one of the DAC input ports, said first combination network producing values on said M output ports from combinations of the values on said P input ports;
• and
• a second combination network coupled to receive the analog outputs of each of said DACs and providing a combined analog output signal as a combination of the DAC outputs.

Apparatus for use with an input sample clock having F.sub.S effective edges per unit time, for use further with a sample input signal having samples which occur in coordination with said effective edges of said input sample clock, comprising:

• a clock generator coupled to receive said input sample clock and generating a generated clock signal having MF.sub.S effective edges per said unit time in response to said input sample clock, M<0 and M.noteq.1;
• a discrete time filter coupled to receive said sampled input signal and said generated clock signal, and producing an output signal updated at the frequency MFs;
• and
• a digital to analog converter (DAC) coupled to receive the output signal of said filter and to produce an analog output signal in response thereto.

A method for filtering a sampled input signal, comprising the steps of:

• filtering said input signal through P filters, each producing a respective output signal, P>1;
• combining the output signals of said P filters to produce M intermediate signals, 1<M.ltoreq.P;
• converting each of said M intermediate signals to a respective analog signal;
• and
• combining said analog signals.

A method for filtering a sampled input signal to produce an analog output signal, for use with an input sample clock having F.sub.S effective edges per unit time, the samples of said sampled input signal occurring in coordination with said effective edges of said input sample clock, comprising to steps of:

• generating a generated clock signal having MF.sub.S effective edges per said unit time in response to said input sample clock, M>0 and M.noteq.1;
• discrete-time filtering said sampled input signal to produce a filtered output signal updated in response to each effective edge of said generated clock signal;
• and
• converting said filtered output signal to said analog Output signal.