The use of an adequate gate bias resistor
was shown to be useful in producing a wide linearity sweet-spot in junction FET devices.
An innovative amplifier design has been developed that allows traditional medium power Darlington feedback amplifiers to operate directly from 5 V without the need for an external bias resistor
. The patent-pending design has been applied to the Sirenza Microdevice 5 V InGaP SBB gain block product series.
An obvious example is using just one external "bias" resistor to avoid over-dimensioning the analog circuitry to allow for the inherent [+ or -]30 percent variation that comes with the on-chip bias resistor
. Sometimes it is worthwhile using trimming of circuit elements by automatic tuning techniques (in RF) or by trimming at wafer probe.
The detector diode operates under very high bias resistor
; therefore, [eta][V.sub.T] [much less than] [I.sub.d][R.sub.b].
The control voltage [V.sub.c] is applied to the diodes through the bias resistor
[R.sub.b] and a [lambda]/4 transmission line.
The base bias resistor
must take this voltage drop into account.
By placing the bias resistor
[R.sub.b] close to the feed line, the forward transmission coefficient |[S.sub.21]| has a broadband response and the RF leakage signal is minimized over a wider range of frequencies.
The only minor modification to the high pass/low pass 22.5[degrees] bit was the addition of a 1 to 2 k[ohm] bias resistor
from the PHEMT drain to ground to avoid a floating bias potential.
For systems where the ambient temperature does change, an optional ambient temperature bias resistor
is available, which balances out the effects of changing temperature.
This time constant is minimized by using the smallest FET device geometry and by setting the gate bias resistor
to the lowest value without degrading isolation.
If necessary, these times can be reduced to 15 ns by reducing the bias resistor
to 1 k[ohms].
To ensure minimum gain change over the operating temperature, a voltage drop of 2 V minimum is recommended for the bias resistor