# Gate current for HMC487 Amplifier

Hi,

For the amplifier HMC487LP5, to reduce power consumption and continuous power dissipation, I'm planning to switching the Gate(Vgg) supply, between [Gate voltage at which Amplifier in OFF condition] and [amplifier operating voltage].

In datasheet, Gate bias voltage operating voltage and absolute max. rating both are mentioned as -2V to 0V

Kindly let me know the following,

1. Gate voltage(Vgg) for amplifier OFF condition, even when drain voltage(+7V) is applied.
2. What will be gate bias current for Amplifier OFF and Amplifier ON condition ?
3. Does the operating voltage, (i.e) the voltage, Vgg, at which Idd=1300mA, vary device to device ? What will be the performance impact if, the Vgg of one amplifier is set for another amplifier. We are using two amplifiers, to get +36dBm output, can both amplifier set at same Vgg?

Regards,

Kanchana R

• Hi Kanchana R,

1. For this type of part a gate voltage of -2.0 V is usually considered adequate to turn the amplifier "OFF" (i.e., channel in pinch-off).

2. For the amplifier ON condition (quiescent Idd=1300 mA) the gate current will typically be somewhere in the range of 2 mA - 5 mA, primarily determined by the gate voltage divided by an internal resistor of value 100 ohms (approximately) to ground.

3. The Vgg voltage at which quiescent Idd=1300 mA is achieved will vary a bit from device to device, lot to lot, and also with Vdd and temperature. You can use a single DC supply to provide Vgg for more than one amplifier, but you will likely not get *exactly* the same Idd for both; they could differ by a few or even tens of mA. Whether or not that degree of variation is acceptable may depend upon your application. I would expect to see more variation between devices from different lots than between devices from a single lot. The attached plots and histograms should help to provide an understanding of the type of variation that could be seen and the performance impact that could result.

To simplify biasing we offer a line of Active Bias Controllers (ABCs), which automatically adjust the gate voltage to provide a constant drain current that is stable over supply, temperature, and process variations. To simplify their use, the ABC data sheets contain charts of settings and values compatible with the operation of specific amplifiers. An example of an ABC compatible with the HMC487LP5 is the HMC980:

http://www.analog.com/en/products/power-management/linear-regulators/hmc980.html

I hope that helps.

Regards,

SMcBride

• This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

Thank you,