1 LTC1340 low noise, voltage-boosted varactor driver frequency (120khz/div) 0db relative power (10db/div)
1340 ta02 900mhz
v cc = 3v
c out = 270pf spectral plot of vco output driven by LTC1340 resolution bandwidth = 300hz descriptio n u features the ltc ? 1340 is a varactor diode driver designed to generate 5v varactor drive from a single 3v or higher voltage supply. it includes a low noise amplifier with an internal gain of 2.3 and a self-contained charge pump to generate output volt- ages above the input supply. the amplifier input stage includes a built-in offset voltage that allows the output voltage to swing to ground without requiring ov on the input. this feature maintains the phase detector within its linear range of operation. the LTC1340 requires only three external surface mount capacitors to implement a complete varactor driver module. the LTC1340 features output referred noise of 15 m v rms , minimizing frequency deviation in pll frequency synthe- sizer systems. supply current is 400 m a typically with a 3v supply, and drops to 1 m a in shutdown, maximizing operating life in battery-powered systems. amplifier bandwidth is user- adjustable from 10khz up to 500khz and the output typically sinks or sources 20 m a, allowing fast output signal changes with a typical varactor load. the amplifier input features rail- to-rail input common mode range, allowing it to interface with the output of virtually any phase detector circuit. the LTC1340 is available in ms8 and so-8 packages. typical applicatio n u low voltage frequency synthesizer LTC1340 pgnd cp vco av cc a v = 2.3 v cc 0v to 5v in 18 7 6 2 3 4 5 3v 1340 ta01 out loop
filter shdn shutdown agnd 270pf 0.1 m f 0.1 m f phase
detector , ltc and lt are registered trademarks of linear technology corporation. n generates 5v varactor drive from a 3v supply n wide supply voltage range: 2.7v to 6v n requires only three external components n micropower operation: 400 m a at 3v supply n shutdown mode drops supply current below 1 m a n low output noise: 15 m v rms n amplifier gain: 2.3 n up to 500khz signal bandwidth n ms8 and so-8 packages n very low input bias current: 10na max n amplifier offset maintains phase detector in linear region applicatio n s u n 5v varactor drive from a single li-ion cell n 5v varactor drive from three nicd/nimh cells n cellular telephones n portable rf equipment n radio modems n wireless data transmission
2 LTC1340 absolute m axi m u m ratings w ww u supply voltage (v cc ) ................................................. 7v input voltage (av cc ) ............................................... 14v input voltage (shdn, in) ............... C 0.3v to v cc + 0.3v output voltage (cp, out) ............ C 0.3v to av cc + 0.3v output short-circuit duration .......................... indefinite commercial temperature range ................. 0 c to 70 c extended commercial operating temperature range (note 1) ............. C 40 c to 85 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec.) ................. 300 c package/order i n for m atio n w u u t jmax = 125 c, q ja = 200 c/ w 1
2
3
4 cp
v cc
shdn
pgnd 8
7
6
5 av cc
out
agnd
in top view ms8 package
8-lead plastic msop LTC1340cms8 order part number order part number LTC1340cs8 ms8 part marking s8 part marking ltbm 1340 av cc
out
agnd
in cp
v cc
shdn
pgnd s8 package
8-lead plastic so top view 1
2
3
4 8
7
6
5 t jmax = 125 c, q ja = 130 c/ w consult factory for industrial and military grade parts. symbol parameter conditions min typ max units v cc input supply voltage l 2.7 6 v i cc supply current i out = 0, 2.7v v cc 6v l 500 900 m a shutdown, 2.7v v cc 6v l 110 m a v ol low output voltage swing v cc = 2.7v, 6v, ? i out ? = 0 m a l 0.25 v v cc = 2.7v, 6v, ? i out ? = 14 m a l 0.6 v v oh high output voltage swing v cc = 2.7v, ? i out ? = 0 m a l 4.6 v v cc = 6v, ? i out ? = 0 m a l 10.5 v v cc = 2.7v, ? i out ? = 14 m a l 4.25 v v cc = 6v, ? i out ? = 14 m a l 9.75 v i out output sink/source current 0.6v v out 4.25v, v cc = 2.7v l 14 20 35 m a 0.6v v out 9.75v, v cc = 6v l 14 20 35 m a t out output transition time c out = 1nf, d v out = 4v l 200 285 m s v in input voltage range l 0v cc v i b input bias current 0.1v v in v cc 0.01 1na l 10 na v os input offset voltage l 0.15 0.35 0.60 v a v amplifier gain v in = 1v, av cc = 5v l 2.1 2.3 2.5 v/v g m amplifier transconductance v out = 2.5v, av cc = 5v 1200 1800 2300 m mho v out = 2.5v, av cc = 5v l 800 3200 m mho r out output impedance v out = 1/2av cc 1m w e n output noise voltage 1khz to 100khz, c out = 1nf 15 25 m v rms bw C 3db signal bandwidth c out = 1nf 125 khz psrr power supply rejection ratio av cc = 4v to 6v, c out = 1nf l 60 90 db i shdn shutdown logic input current 0.1v v shdn v cc 0.01 1 m a electrical characteristics t a = 25 c, unless otherwise noted. (note 1)
3 LTC1340 electrical characteristics symbol parameter conditions min typ max units t start charge pump start-up time c cp = 0.1 m f, v cc = 2.7v, i out = 0 l 1.2 5 ms v ripple charge pump output ripple at c p c cp = c vcc = 0.1 m f, v cc = 2.7v, i out = 0 (note 2) 200 m v p-p f cp charge pump frequency (note 3) l 2.5 4 mhz the l denotes specifications which apply over the specified temperature range. note 1: c grade device specifications are guaranteed over the 0 c to 70 c temperature range. in addition, c grade device specifications are assured over the C 40 c to 85 c temperature range by design or correlation, but are not production tested. t a = 25 c, unless otherwise noted. (note 1) output high voltage (v) 9.4
9.3
9.2
9.1
9.0
8.9
4.9
4.8
4.7
4.6
4.5
4.4 1340 g04 temperature ( c) ?0 0 25 25 50 75 100 125
c out = 1nf
v in = v shdn = v cc i oh = 0, v cc = 5v i oh = 0, v cc = 2.7v i oh = 14 m a, v cc = 5v i oh = 14 m a, v cc = 2.7v output high voltage vs temperature output low voltage (v) 0.5
0.4
0.3
0.2
0.1
0 1340 g05 temperature ( c) ?0 0 25 25 50 75 100 125 v cc = 2.7v or 5v
c out = 1nf
v in = 0v
v shdn = v cc i ol = 14 m a i ol = 0 supply voltage (v) 2.5 transconductance ( m mho) 3.5 3.0 4.5 4.0 5.5 6.0 5.0 6.5 1340 g06 2100
2050
2000
1950
1900
1850
1800 t a = 25 c
v out = 1/2av cc
v shdn = v cc dc transfer curve input voltage (v) 0 output voltage (v) 12
11
10
9
8
7
6
5
4
3
2
1
0 1 234 1340 g01 56 v cc = 2.7v v cc = 5v t a = 25 c
c out = 1nf
i out = 0
v shdn = v cc v cc = 6v temperature ( c) ?0 input offset voltage (v) 0 0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15 1340 g03 25 25 50 75 100 125 v cc = 2.7v to 6v
c out = 1nf
v shdn = v cc frequency (khz) 1 voltage gain (db) phase shift (deg) 20
10
0
10
20
30
40
50
60
70
80
?0 180
144
108
72
36
0
36
72
108
144
180
216 10 100 1000 1340 g02 v cc = 2.7v
t a = 25 c
c out = 1nf phase gain gain and phase shift vs frequency typical perfor m a n ce characteristics u w input offset voltage vs temperature output low voltage vs temperature transconductance vs supply voltage note 2: the charge pump output ripple is not tested but is correlated with a pcb ground plane and high quality, low esr, low esl metalized polyester 0.1 m f capacitors. note 3: the internal oscillator typically runs at 2mhz, but the charge pump refreshes the output on both phases of the clock, resulting in an effective 4mhz operating frequency.
4 LTC1340 transconductance ( mho) 3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000 1340 g07 temperature ( c) ?0 0 25 25 50 75 100 125 v cc = 6v v out = 1/2av cc
v shdn = v cc v cc = 5v v cc = 2.7v typical perfor m a n ce characteristics u w temperature ( c) ?0 supply current ( m a) 0 700
650
600
550
500
450
400
350
300 1340 g09 25 25 50 75 100 125 v shdn = v cc v cc = 6v v cc = 5v v cc = 2.7v supply current vs temperature transconductance vs temperature gsm 900 ms spectrum due to modulation frequency from the carrier(khz) 0 ?6 relative power (db) 10
0
10
20
30
40
50
60
80
?0 400 1200 1800 1340 g10 200 600 3000 6000 ?0
measurement
bandwidth
30khz measurement
bandwidth
100khz data taken on
ltc demo board dc152 LTC1340 supply voltage (v) 2.5 supply current ( m a) 3.5 3.0 4.5 4.0 5.5 6.0 5.0 6.5 1340 g08 900
800
700
600
500
400
300
200 t a = 25 c
v shdn = v cc supply current vs supply voltage rail-to-rail step response at v cc = 2.7v v in = 0.3v to 2.6v c out = 1nf 1340 g15 0v 10000
1000
100
10
1
1340 g12 input bias current (pa) temperature ( c) ?0 0 25 25 50 75 100 125 v in = v shdn = v cc = 5v output voltage noise ( v/ rms ) 25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.50
5.0
1.50
0
1340 g11 temperature ( c) ?0 0 25 25 50 75 100 125 av cc = 5v
c out = 1nf output voltage noise vs temperature input bias current vs temperature temperature ( c) ?0 shutdown input threshold (v) 0 2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8 1340 g13 25 25 50 75 100 125 v cc = 6v v cc = 5v v cc = 4v v cc = 3v v cc = 2.7v shutdown input threshold vs temperature rail-to-rail step response at v cc = 6v 0v v in = 0.3v to 6v c out = 1nf 1340 g14
5 LTC1340 pi n fu n ctio n s uuu in (pin 5): signal input. the internal amplifier amplifies the signal input at this pin typically by 2.3 to the out pin. in accepts signals from gnd to v cc without phase rever- sal or unusual behavior, allowing a direct connection to the output of virtually any phase detector or loop filter pow- ered from v cc . agnd (pin 6): signal ground. connect agnd to the ground plane in close proximity to the vco ground. there is an internal parasitic resistance of 50 w between agnd and pgnd. out (pin 7): driver output. out is the output of the internal g m amplifier and the internal feedback network. it swings from gnd to av cc , and drives a varactor load directly. the out pin requires an external capacitor ( 3 220pf) to agnd to ensure stability. out typically sinks or sources 20 m a. av cc (pin 8): amplifier supply. ltc recommends a direct connection from av cc to cp and also recommends a 0.1 m f filter capacitor from cp to pgnd. cp (pin 1): charge pump output. this is the output of the internal charge pump. the voltage at cp is nominally twice the v cc input voltage. connect cp to an external 0.1 m f filter capacitor and av cc . v cc (pin 2): supply input. this is the input supply to the charge pump. v cc can range from 2.7v to 6v and requires a 0.1 m f bypass capacitor to pgnd. shdn (pin 3) shutdown. if shdn is high (>v cc C 0.5v), the LTC1340 operates normally. if shdn is pulled low (< 0.5v), the LTC1340 enters shutdown mode and the supply current drops to less than 1 m a typically. in shut- down, the charge pump output voltage collapses and the out pin enters a high impedance state. if shdn returns high, the charge pump output requires 1.2ms typically to resume full voltage. pgnd (pin 4): power ground. this is the charge pump ground. connect pgnd to the system power supply return. frequency (mhz) 4.0
3.8
3.6
3.4
3.2
3.0 1340 g16 temperature ( c) ?0 0 25 25 50 75 100 125 v shdn = v cc v cc = 6v v cc = 2.7v v cc = 5v charge pump frequency vs temperature small-signal response 1340 g18 c out = 220pf c out = 470pf c out = 1nf c out = 0pf typical perfor m a n ce characteristics u w large-signal response v in = 0.5v to 2v v cc = 2.7v c out = 1nf 1340 g17 0v
6 LTC1340 block diagra m w applicatio n s i n for m atio n wu u u overview the LTC1340 is a monolithic ic that combines a charge pump and a low noise amplifier to provide a 0v to 5v swing to drive a varactor diode-based pll system from a single 3v supply. traditional pll frequency synthesizers used in cellular phones and other portable rf systems use varactor diodes as the voltage variable element in the vco. typical varactor diodes require at least 4v of control voltage swing to obtain their full range of capacitance adjustment. newer battery-powered systems, operating from low voltage power supplies, have trouble providing this bias voltage without an additional step-up circuit. the LTC1340 design provides a 5v signal swing suitable for biasing such a varactor diode when powered from a 3v or higher voltage supply. the internal op amp and feed- back network with built-in offset provide a gain of 2.3 so that a 0.35v to 2.5v swing at the noninverting input provides a 0v to 5v swing at the output. the onboard charge pump provides the boosted voltage necessary to drive the varactor and requires only a single 0.1 m f output filter capacitor to complete the boost circuit. the amplifier requires one capacitor (typically 1nf) at its output to set amplifier noise bandwidth and to ensure amplifier stabil- ity. the performance characteristics of the LTC1340 are designed to meet the requirements of gsm and similar cellular phone transceivers without requiring additional circuitry. the LTC1340s high level of functional integra- tion allows it to replace several power supply and regulator components in a typical pll synthesizer. this results in significant space and complexity savings. charge pump the LTC1340 features a self-contained doubling charge pump with internal flying capacitors. the charge pump refreshes the output on each phase of the internal 2mhz clock, giving an effective 4mhz switching frequency. an external 0.1 m f capacitor at the cp pin acts as a charge reservoir and provides filtering to minimize clock feedthrough to the amplifier section. the cp pin can be connected directly to the amplifier power supply at av cc . in addition, it can be filtered with an rc or lc network prior to its connection to av cc . the LTC1340 minimizes inter- action between the charge pump and the amplifier through careful internal shielding. amplifier the LTC1340 includes an internal g m amplifier with an on- chip feedback network to amplify the input signal to the gained output level. the amplifier requires an external capacitor from its output to agnd to provide closed-loop stability, noise bandwidth limiting and to further reduce charge pump feedthrough. the C 3db signal bandwidth of the amplifier is given by the following equation: bw C3db = g m /(2 p )( c out )(a v ) LTC1340 pgnd cp av cc v cc shdn doubler
charge
pump with
internal
flying
capacitor in 50 w pgnd 1340 bd 62.3pf 1.15m v s
0.62v out
20 m a agnd c cp
0.1 m f
(external) 0.1 m f c out
(external) 1.5m 47.9pf + +
7 LTC1340 applicatio n s i n for m atio n wu u u should require no additional filtering. additional filtering to reduce feedthrough noise is possible by inserting a resistor or a ferrite bead between out and c out . hookup the two sections of the LTC1340 are carefully shielded from each other inside the chip, but care must also be taken in the external hookup to minimize noise at the amplifier output. the two halves of the chip should only meet electrically where the cp and av cc pins connect together and at the common point of agnd and pgnd. separate pgnd and agnd as much as possible. agnd is the amplifier ground. connect it to a ground plane and as close to the vco ground as possible. bypass v cc and cp to pgnd with a 0.1 m f capacitor. select high quality, low esr and low esl surface mount ceramic capacitors for both the cp and the vcc bypass capacitors. poor grade capacitors will result in unacceptable ripple amplitude or ringing characteristics. connect both terminals of the bypass capacitors as close to the chip as possible to minimize charge pump output ripple amplitude and ground currents in the rest of the system. keep in and out away from v cc , cp and av cc as much as possible. crosstalk from v cc , cp and av cc pcb traces to in and out pcb traces can be minimized by routing agnd pcb traces as shield as shown in figures 1 and 2. connect the 1nf output capacitor close to the varactor diode and return it to the agnd plane. the shdn and in pins, should not be allowed to go below pgnd potential as the esd diode forms an npn and bleeds the charge pump output. amplifier transconductance is typically 1800 m mho. with a 1nf external capacitor at the amplifier output, the band- width is 125khz. the amplifier transconductance varies with temperature and process. the minimum recom- mended c out is 220pf with a typical bandwidth of 566khz. the slew rate of the amplifier is: sr = i out /c out the amplifier typically sinks or sources 20 m a, allowing it to slew a 1nf output capacitance at 20v/ms, or 5v in 250 m s. the on-chip amplifier feedback network is set for a dc gain of 2.3 with an input offset of 0.35v as shown in the typical curves. the amplifier allows a rail-to-rail input swing with a 3v supply and provides a 5v swing at the output. the output swings to within millivolts of the av cc voltage and to about 100mv above agnd. the input stage of the amplifier is powered from av cc and accepts full gnd to v cc rail-to-rail input signals without exceeding the input common mode range. the output noise of the amplifier is typically 15 m v rms at frequencies between 1khz and 100khz. there are two feedthrough signals at the amplifier out pin from the charge pump, the main component at 4mhz and the second harmonic signal at 8mhz. the 4mhz feedthrough is typically below 50 m v with c out equal to 1nf and c cp equal to 0.1 m f. the feedthrough signal decreases in amplitude when larger c out is used. most systems figure 1. suggested surface mount pcb layout for LTC1340cs8 0.1 m f 0.1 m f LTC1340cs8 1nf varactor
diode 1340 f01 pin 1 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
8 LTC1340 applicatio n s i n for m atio n wu u u 1340f lt/tp 0697 7k ? printed in usa ? linear technology corporation 1997 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 l (408) 432-1900 fax: (408) 434-0507 l telex: 499-3977 l www.linear-tech.com part number description comments ltc1261, ltc1429, gaas fet bias generators regulated negative voltage generator from a single positive supply ltc1550, ltc1551 related parts 0.016 ?0.050
0.406 ?1.270 0.010 ?0.020
(0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010
(0.203 ?0.254) so8 0695 0.053 ?0.069
(1.346 ?1.752) 0.014 ?0.019
(0.355 ?0.483) 0.004 ?0.010
(0.101 ?0.254) 0.050
(1.270)
bsc 1 2 3 4 0.150 ?0.157**
(3.810 ?3.988) 8 7 6 5 0.189 ?0.197*
(4.801 ?5.004) 0.228 ?0.244
(5.791 ?6.197) dimension does not include mold flash. mold flash
shall not exceed 0.006" (0.152mm) per side
dimension does not include interlead flash. interlead
flash shall not exceed 0.010" (0.254mm) per side
*
** dimensions in inches (millimeters) unless otherwise noted. package descriptio n u 0.1 m f 0.1 m f LTC1340cms8 pin 1 1nf varactor
diode 1340 f02 figure 2. suggested surface mount pcb layout for LTC1340cms8 ms8 package 8-lead plastic msop (ltc dwg # 05-08-1660) msop08 0596 * dimension does not include mold flash, protrusions or gate burrs. mold flash,
protrusions or gate burrs shall not exceed 0.006" (0.152mm) per side
** dimension does not include interlead flash or protrusions.
interlead flash or protrusions shall not exceed 0.006" (0.152mm) per side 0.021 0.004
(0.53 0.01) 0 ?6 typ 0.007
(0.18) seating
plane 0.040 0.006
(1.02 0.15) 0.012
(0.30)
0.006 0.004
(0.15 0.10) 0.025
(0.65)
typ 12 3 4 0.192 0.004
(4.88 0.10) 8 7 6 5 0.118 0.004*
(3.00 0.10) 0.118 0.004**
(3.00 0.10) s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610)
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