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Gain Block Specification Selection Guide
Bias Range
(Vcc, Vc, Vd; Icc, Ic, Id)
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- What:
- Vd: The power supply voltage for best operation in volts.
- Typically the Vd requirement is set by the power supply the designer has available and is not negotiable - though you can always choose a device with a Vd lower than the available supply voltage. Note that MSA products are actually current controlled not voltage controlled. For these products the voltage quoted assumes the use of an ~2 V drop across a bias resistor to change the voltage rail into a current source and provide some temperature stability for the bias. If the designer uses an active bias circuit the voltage drop will be reduced to ~1V so these devices can be used to 1V lower that the voltage quoted. HPMX INA and MGA devices can be treated as voltage controlled i.e. their bias remains relatively stable over temperature when the IC is biased directly from a fixed voltage source.
- Id: The amount of bias current the device draws in mA.
- For an IC the biasing circuit is internal so once a Vd is selected the Id is determined. More Id means less battery life for handheld equipment. It also means higher efficiency which translates into cooler operation and longer lifetime. Alternatively it usually means more output power capability and greater linearity (less distortion). An interesting figure of merit is dB/mA the amount of gain available for the current drawn.
- Direction:
- Vd: needs to fit application
- Id: Assuming performance is adequate less Id is better.
- Range:
- Vd: 3-6 V for handheld, to greater than 18 V for "plugged-in"
- Id: 4 - 325 mA
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