L8221

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

5 of 5

www.unisonic.com.tw

QW-R123-020.a



TEST CIRCUIT

The above is partial application circuit for the UTC L8221 series showing all external components required for

appropriate biasing. The bias circuits are unconditionally stable over the full temperature range with the associated

FETs and gate and drain capacitors in circuit. Capacitors C1 and C2 ensure that residual power supply and

substrate generator noise is not allowed to affect other external circuits which may be sensitive to RF interference.

They also serve to suppress any potential RF feed through between stages via the UTC L8221 device. These

capacitors are required for all stages used. Values of 10nF and 4.7nF respectively are recommended however this is

design dependent and any value between 1nF and 100nF could be used.

The capacitor CSUB is an integral part of the UTC L8221’s negative supply generator. The negative bias voltage

is generated on-chip using an internal oscillator. The required value of capacitor CSUB is 47nF. This generator

produces a low current supply of approximately -3 volts. Although this generator is intended purely to bias the

external FETs, it can be used to power other external low current circuits via the CSUB pin.

The UTC L8221 devices have been designed to protect the external FETs form adverse operating conditions.

With a JFET connected to any bias circuit, the gate output voltage of the bias circuit can not exceed the range

-3.0V~1V under any conditions, including power up and power down transients. Should the negative bias generator

be shorted or overloaded so that the drain current of the external FETs can no longer be controlled, the drain supply

to FETs is shut down to avoid damage to the FETs by excessive drain current. The UTC L8221 incorporates over

and under voltage protection so is the receiver or installation develops a fault the LNB will shut down and restart

once operating conditions are back to normal.

UTC assumes no responsibility for equipment failures that result from using products at values that

exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or

other parameters) listed in products specifications of any and all UTC products described or contained

herein. UTC products are not designed for use in life support appliances, devices or systems where

malfunction of these products can be reasonably expected to result in personal injury. Reproduction in

whole or in part is prohibited without the prior written consent of the copyright owner. The information

presented in this document does not form part of any quotation or contract, is believed to be accurate

and reliable and may be changed without notice.