Direct radio-frequency to digital conversion with filtering of comparator outputs

The invention concerns a flash analogue-to-digital converter (ADC) for performing direct RF to digital conversion. A radio-frequency input signal 102 is compared with a plurality of reference voltages 104a, 104b to generate a plurality of comparison signals 108a, 108b. A first one of the comparison signals 108a is input to a first filter 110a, which outputs a first filtered signal 112a. A second one of the comparison signals 108b is input to a second filter 110b, which output a second filtered signal 112b. A digital output signal 116 is generated 114 at least on the basis of the first filtered signal 112a and the second filtered signal 112b. The first and second filtered signals may first undergo additional filtering in third 120a and fourth 120b filters respectively. The first and second filters may sample the first and second comparison signals using a first clock rate 118a and the second and third filters may sample the first and second filtered signals using a different second clock rate 118b. Alternatively, the outputs of both the first and second filters may be input to a single common third filter (120, Fig. 5). The filters may be digital filters. The generating step 114 may involve thermometer code to binary code conversion. Each of the first and second filters may receive multiple comparison signals as inputs (Fig. 3).