Fast current-mode analog circuit for converting video data signals between color space formats

A current-mode color space converter to convert Y, C.sub.b and C.sub.r signals to G, R and B signals, comprising:

• a Y conversion circuit to compute Y contributions to the G, R and B signals, the Y conversion circuit including:
• a first folded cascode structure having an input coupled to an analog Y signal and a Y current output;
• and
• a first current mirror that generates from the Y current output the Y contributions to the G, R and B signals;
• a C.sub.b conversion circuit to compute C.sub.b contributions to the G and B signals, the C.sub.b conversion circuit including:
• a second folded cascode structure having an input coupled to an analog C.sub.b signal and a C.sub.b current output;
• a first current divider providing first and second divided C.sub.b currents representing specific respective fractions of the C.sub.b current output;
• a second current mirror that generates from the first divided C.sub.b current the C.sub.b contribution to the B signal;
• and
• a first current adder that subtracts from the second divided C.sub.b current a first difference current to provide the C.sub.b contribution to the G signal;
• and
• a C.sub.r conversion circuit to compute C.sub.r contributions to the G and R signals, the C.sub.r conversion circuit including:
• a third folded cascode structure having an input coupled to an analog C.sub.r signal and a C.sub.r current output;
• a second current divider providing first and second divided C.sub.r currents representing specific respective fractions of the C.sub.r current output;
• a third current mirror that generates from the first divided C.sub.r current the C.sub.r contribution to the R signal;
• and
• a second current adder that subtracts from the second divided C.sub.r current a second difference current to provide the C.sub.r contribution to the G signal.

A current-mode color space converter to convert first color space signals to second color space signals, comprising:

• first color space current-mode conversion circuits to compute first color space contributions to the second color space signals, each conversion circuit including (A) a respective low-impedance current-input structure having an input coupled to a respective analog first color space signal, each conversion circuit generating a respective first color space current output;
• (B) at least one respective current mirror that generates from the first color space current output an unadjusted first color space contribution to at least one of the second color space signals, and (C) at least one current adder for subtracting respective offset currents from said unadjusted first color space contribution to said at least one of said second color space signals to provide the first color space contribution to at least one of the second color space signals;
• and
• a plurality of current-mode adders that respectively add said contributions to the second color space signals to generate the second color space signals.