Measure wide range of current 800 µA - 1.5 A
How much accuracy do you need? If you only need an estimate, then a series silicon diode will give you more or less logarithmic indication over a wide range of currents.

The main problem with a diode, the variation in voltage drop with temperature, can be significantly mitigated by running a second diode at the same temperature with a reference current. Two diodes within a rectifier bridge would be thermally coupled and ideal for this, I've marked the connections on the schematic, bridge +ve stays unused. As your load is very low power and the high currents are only short pulses, even two individual diodes taped together should be OK. A 1N540x for instance is good for 3&nbsp;A continuous and will still have a significant forward drop at 100&nbsp;µA.

It has the advantage that the load voltage changes very little, perhaps a few hundred mV between 500&nbsp;µA and 1.5&nbsp;A, much less than with a resistive shunt that will measure mA.







simulate this circuit &ndash; Schematic created using CircuitLab

Replacing R1 with a current sink would make the reference current more accurate, but (power supply voltage - 0.7&nbsp;V)/R1 is probably adequate for most purposes. Ideally, the reference current would be in the middle of the range you want to measure best. Somewhere in the 1 to 10&nbsp;mA range feels good.

The voltmeter reading will be proportional to the log of the ratio of load to reference current. The output impedance from the diodes is very low, so amplifying the difference with an opamp, perhaps to scale it or to ground-reference it, will be straightforward.

You will need to calibrate the measurement conversion at high and low currents to establish the log law, and it would be good to check it at a few points in between. Remember that calibrating at high current will heat the load diode, so you may need to use short pulses, as short as your transmit pulses, to minimise thermal drift errors.