fet bias controller issue 2 - june 1998 device description the znbg series of devices are designed to meet the bias requirements of gaas and hemt fets commonly used in satellite receiver lnbs, pmr, cellular telephones etc. with a minimum of external components. with the addition of two capacitors and resistors the devices provide drain voltage and current control for a number of external grounded source fets, generating the regulated negative rail required for fet gate biasing whilst operating from a single supply. this negative bias, at -3 volts, can also be used to supply other external circuits. the znbg4000/1 and znbg6000/1 contain four and six bias stages respectively. in setting drain current the znbg4000/1 two resistors allows individual fet pair control to different levels, the znbg6000/1 two resistors split control between two and four fets. this allows the operating current of input fets to be adjusted to minimise noise, whilst the following fet stages can separately be adjusted for maximum gain. the series also offers the choice of drain voltage to be set for the fets, the znbg4000/6000 gives 2.2 volts drain whilst the znbg4001/6001 gives 2 volts. these devices are unconditionally stable over the full working temperature with the fets in place, subject to the inclusion of the recommended gate and drain capacitors. these ensure rf stability and minimal injected noise. it is possible to use less than the devices full complement of fet bias controls, unused drain and gate connections can be left open circuit without affecting operation of the remaining bias circuits. in order to protect the external fets the circuits have been designed to ensure that, under any conditions including power up/down transients, the gate drive from the bias circuits cannot exceed the range -3.5v to 0.7v. furthermore if the negative rail experiences a fault condition, such as overload or short circuit, the drain supply to the fets will shut down avoiding excessive current flow. the znbg4000/1 and znbg6000/1 are available in qsop16 and 20 pin packages respectively for the minimum in devices size. device operating temperature is -40 to 70c to suit a wide range of environmental conditions. features provides bias for gaas and hemt fets drives up to four or six fets dynamic fet protection drain current set by external resistor regulated negative rail generator requires only 2 external capacitors choice in drain voltage wide supply voltage range qsop surface mount package applications satellite receiver lnbs private mobile radio (pmr) cellular telephones znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-137
absolute maximum ratings supply voltage -0.6v to 15v supply current 100ma drain current (per fet) 0 to 15ma (set by r cal1 and r cal2 ) output current 100ma operating temperature -40 to 70c storage temperature -50 to 85c power dissipation (t amb = = 25c) qsop16 500mw qsop20 650mw electrical characteristics test conditions (unless otherwise stated): t amb = = 25c,v cc =5v,i d =10ma (r cal1 =33k w ;r cal2 =33k w w ) symbol parameter conditions limits units min typ max v cc supply voltage 5 12 v i cc supply current znbg4000/1 i d1 to i d4 =0 i d1 to i d4 =10ma 10 50 ma ma i cc supply current znbg6000/1 id1 to i d6 =0 i d1 to i d6 =10ma 15 75 ma ma v sub substrate voltage (internally generated) i sub = 0 i sub = -200 m a -3.5 -3 -2 -2 v v e nd e ng output noise drain voltage gate voltage c g =4.7nf, c d =10nf c g =4.7nf, c d =10nf 0.02 0.005 vpkpk vpkpk f o oscillator freq. 200 350 800 khz drain characteristics i d current 8 10 12 ma current change d i dv with v cc v cc =5 to 12v 0.02 %/v d i dt with t j t j =-40 to +70c 0.05 %/c v d voltage znbg4000, zngb6000 znbg4001, znbg6001 2 1.8 2.2 2 2.4 2.2 v v voltage change d d v dv with v cc v cc = 5 to 12v 0.5 %/v d d v dt with t j t j = -40 to +70c 50 ppm znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-138
symbol parameter conditions limits units min typ max gate characteristics i go output current range -30 2000 m a output voltage znbg4000/1 v ol output low i d1 to i d4 =12ma i g1 to i g4 =0 -3.5 -2 v i d1 to i d4 =12ma i g1 to i g4 = -10 m a -3.5 -2 v v oh output high i d1 to i d4 = 8ma i g1 to i g4 = 0 0 1 v output voltage znbg6000/1 v ol output low i d1 to i d6 =12ma i g1 to i g6 = 0 -3.5 -2 v i d1 to i d6 =12ma i g1 to i g6 = -10 m a -3.5 -2 v v oh output high i d1 to i d6 = 8ma i g1 to i g6 = 0 0 1 v notes: 1. the negative bias voltages specified are generated on-chip using an internal oscillator. two external capacitors, c nb and c sub , of 47nf are required for this purpose. 2. the characteristics are measured using two external reference resistors r cal1 and r cal2 of value 33k w wired from pins r cal1/2 to ground. for the znbg4000, resistor r cal1 sets the drain current of fets 1 and 2, resistor r cal2 sets the drain current of fets 3 and 4. for the znbg6000, resistor r cal1 sets the drain current of fets 1 and 4, resistor r cal2 sets the drain current of fets 2, 3, 5 and 6. 3. noise voltage is not measured in production. 4. noise voltage measurement is made with fets and gate and drain capacitors in place on all outputs. c g , 4.7nf, are connected between gate outputs and ground, c d , 10nf, are connected between drain outputs and ground. znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-139
jfet drain current v r cal 0204060 100 0 2 4 6 8 10 r cal (k) 80 12 14 16 jfet drain voltage v drain current 2468 16 2.0 2.1 2.2 drain current (ma) 10 2.3 2.4 12 14 v sub v external load 0 0.2 0.4 0.6 1.0 -3.0 -2.5 -2.0 -1.5 -1.0 external vsub load (ma) 0.8 -0.5 0.0 typical characteristics vcc = 5v vcc = 5v 6v 8v 10v vcc = 5v 6v 8v 10v note:- operation with loads > 200a is not guaranteed. znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-140
functional diagram functional description the znbg devices provide all the bias requirements for external fets, including the generation of the negative supply required for gate biasing, from the single supply voltage. the diagram above shows a single stage from the znbg series. the znbg4000/1 contains 4 such stages, the znbg6000/1 contains 6. the negative rail generator is common to all devices. the drain voltage of the external fet q n is set by the znbg device to its normal operating voltage. this is determined by the on board v d set reference, for the znbg4000/6000 this is nominally 2.2 volts whilst the znbg4001/6001 provides nominally 2 volts. the drain current taken by the fet is monitored by the low value resistor i d sense. the amplifier driving the gate of the fet adjusts the gate voltage of q n so that the drain current taken matches the current called for by an external resistor r cal . both znbg devices have the facility to program different drain currents into selected fets. two r cal inputs are provided. for the znbg4000, resistor r cal1 sets the drain current of fets 1 and 2, resistor r cal2 sets the drain current of fets 3 and 4. for the znbg6000, resistor r cal1 sets the drain current of fets 1 and 4, resistor r cal2 sets the drain current of fets 2, 3, 5 and 6. since the fet is a depletion mode transistor, it is usually necessary to drive its gate negative with respect to ground to obtain the required drain current. to provide this capability powered from a single positive supply, the device includes a low current negative supply generator. this generator uses an internal oscillator and two external capacitors, c nb and c sub . znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-141
znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 typical application circuit applications information the above is a partial application circuit for the znbg 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 c d and c g 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 feedthrough between stages via the znbg 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 capacitors c nb and c sub are an integral part of the znbgs negative supply generator. the negative bias voltage is generated on-chip using an internal oscillator. the required value of capacitors c nb and c sub 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 circuits via the c sub pin. resistors r cal1/2 sets the drain current at which all external fets are operated. both znbg devices have the facility to program different drain currents into selected fets. two r cal inputs are provided. for the znbg4000, resistor r cal1 sets the drain current of fets 1 and 2, resistor r cal2 sets the drain current of fets 3 and 4. for the znbg6000, resistor r cal1 sets the drain current of fets 1 and 4, resistor r cal2 sets the drain current of fets 2, 3, 5 and 6. if the same drain current is required for all fets on either device then pins r cal1 and r cal2 can be wired together and shunted to ground by a single calibration resistor of half normal value. if any bias control circuit is not required, its related drain and gate connections may be left open circuit without affecting the operation of the remaining bias circuits. if all fets associated with a current setting resistor are omitted, the particular r cal should still be included. the supply current can be reduced, if required, by using a high value r cal resistor (e.g. 470k). 4-142
znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 applications information (continued) the znbg devices have been designed to protect the external fets from adverse operating conditions. with a jfet connected to any bias circuit, the gate output voltage of the bias circuit can not exceed the range -3.5v to 0.7v, under any conditions including powerup and powerdown 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 following diagrams show the znbg4000/1 and znbg6000/1 in typical lnb applications. within each fet gain stage the numbering system indicates how the bias stages relate to the application circuits. this is important when rcal values are used to set differing drain currents. dual standard or enhanced lnb block diagram 4-143
dual standard or enhanced lnb block diagram . high gain znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 4-144
znbg6000 znbg6001 znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 ordering information znbg4000 znbg4001 part number package part mark znbg4000q16 qsop16 znbg4000 znbg4001q16 qsop16 znbg4001 znbg6000q20 qsop20 znbg6000 znbg6001q20 qsop20 znbg6001 connection diagrams 4-145
package dimensions pin no.1 identification recess for pin 1 a b d c k qsop16 pin millimetres inches min max min max a 4.80 4.90 0.033 0.039 b 0.635 0.025 nom c 0.177 0.267 0.007 0.011 d 0.20 0.30 0.008 0.012 e 3.81 3.99 0.15 0.157 f 1.35 1.75 0.053 0.069 g 0.10 0.25 0.004 0.01 j 5.79 6.20 0.228 0.244 k 0808 zetex plc. fields new road, chadderton, oldham, ol9-8np, united kingdom. telephone: (44)161 622 4422 (sales), (44)161 622 4444 (general enquiries) fax: (44)161 622 4420 zetex gmbh zetex inc. zetex (asia) ltd. these are supported by streitfeldstra?e 19 47 mall drive, unit 4 3510 metroplaza, tower 2 agents and distributors in d-81673 mnchen commack ny 11725 hing fong road, major countries world-wide germany usa kwai fong, hong kong zetex plc 1998 telefon: (49) 89 45 49 49 0 telephone: (516) 543-7100 telephone:(852) 26100 611 fax: (49) 89 45 49 49 49 fax: (516) 864-7630 fax: (852) 24250 494 internet:http://www.zetex.com this publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. the company reserves the right to alter without notice the specification, design, price or conditions of su pply of any product or service. qsop20 pin millimetres inches min max min max a 8.55 8.74 0.337 0.344 b 0.635 0.025 nom c 1.42 1.52 0.056 0.06 d 0.20 0.30 0.008 0.012 e 3.81 3.99 0.15 0.157 f 1.35 1.75 0.053 0.069 g 0.10 0.25 0.004 0.01 j 5.79 6.20 0.228 0.244 k 0808 znbg4000 znbg4000 znbg4001 znbg6000 znbg6001 page number
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