  The new definition of the ampere calls for a quantum current standard able to
deliver a flow of elementary charges per second controlled with a relative
uncertainty of one part in $10^8$. Despite many efforts, nanodevices handling
electrons one by one have never been able to demonstrate such an accuracy. The
alternative route based on applying Ohm's law to the Josephson voltage and
quantum Hall standards recently reached the target uncertainty but this was at
the expense of the application of error corrections, hampering simplicity and
further improvement. As a result, national metrology institutes still lack an
operational quantum current standard. Here, we present a new quantum current
generator, combining both quantum standards and a superconducting cryogenic
amplifier, free of error correction, which provides quantized currents driven
by the Josephson microwave signal. We show that it can realize the ampere
definition with the target uncertainty over a range extended from mA down to
$\mu$A and improve end-user current measurements, which are up to now a hundred
times less accurate. Other prospects include measuring large resistances using
the new current standard in conjunction with a quantum voltmeter and, by
exploiting its low-noise performances, bridging the gap with the lower currents
of other quantum current sources.
