technical note tsh150 and tsh151 demoboard AN572/0299 by g. augustoni ? tsh150 and tsh151 are very high speed voltage feedback operational amplifiers, using stmi- croelectronics bicmos process. they feature a 200v/ m s slew rate, 150mhz gain bandwidth prod- uct and 20ns to 70ns settling time to 0.1% (2v step). the tsh151 has the added advantage of mos inputs. a45 o typical phase margin, for unity gain, makes them easy to use as followers for buffer applica- tions with 50 w loads for example. additional information may be obtained from the respective data sheets. a demonstration board is available for device evaluation (order code sldb-001a). this note illustrates how to use this demoboard and gives some results obtained from a few basic con- figurations. pcb design building a board using the tsh150 and tsh151 does not require specific calculation but a few basic rules must be observed in order to obtain the best dynamic performances and avoid instability prob- lems. use a good ground plane or common return point for power and signals. all tracks must be wide and as short as possible, this is in order to minimize parasitic resistance, capacitance and signal cou- pling. pay special attention to the operational am- plifier negative input parasitic capacitance, so as not to degrade speed performance. parasitic ca- pacitance cannot be totally eliminated therefore use small resistor values to reduce time constants formed with parasitic components. for power supply decoupling use 10 m f tantalum capacitors and 10nf ceramic placed very close to the device supply pins. introduction in r1 50 r4 1k c2 c f -5v +5v c1 out r2 50 r3 1k 4 1 8 c4 2 6 3 7 c3 ts h15x schematic diagram order code : sldb-001a circuit board layout
pcb figure 1 - solder side (1/1) figure 2 - components side (1/1) sldb-001 this demoboard has been designed to show the performances of the ths150 and tsh151 in very simple configurations. the pcb is of a standard epoxy glass type requiring 1/4 watt resistors, 2.54mm pitch capacitors and sma or smb 50 w impedance connectors for the input and output. the input impedance can be selected with r1 and the output impedance with r2. the whole circuit gives an amplifying stage with gain of 1 + r4 r3 . measurements for all the measurements, r1 = 50 w ,r2=50 w and the following test equipements with 50 w input mode have been used. (note there is a 6db loss due to a resistor bridge formed with r2 and the test equipment input which is corrected on each dia- gram). . hp54100a digitizing scope 1ghz bandwidth . hp8160a pulse generator 3ns rise time . hp3577a network analyser 5hz - 200mhz a 6db amplifying stage r3 = 1k w ,r4=1k w the first measurement was performed by applying a 4mhz 2vpp square wave to the input. the follow- ing are the oscilloscope traces. for both devices, see figures 3 and 4. on figure 4 (ths151) there is a 15% overshoot and on figure 3 (ths150) there is a 5% overshoot. slew rate performances are the same for both 200v/ m s, but the settling time is much shorter for tsh150. hp8160a + hp54100a r3 = 1k w ,r4=1k w ,c f =0 1v/div 50ns/div figure 3 - tsh150 the result can be improved by reducing the values r3 and r4 or by adding a few pf of feedback capacitance c f , adjusted to minimize settling time and overshoot. hp8160a + hp54100a r3 = 1k w ,r4=1k w ,c f =0 50ns/div 1v/div figure 4 - tsh151 technical note 2/4
c f is used to compensate unavoidable parasitic input capacitance by introducing a zero to cancel the pole formed by the input rc network. figures 5 and 6 show the overshoot reduction and settling time improvement without a change in slew rate. hp8160a + hp54100a r3 = 1k w ,r4=1k w ,c f = 3.3pf 1v/div 50ns/div figure 5 - tsh150 hp8160a + hp54100a r3 = 1k w ,r4=1k w ,c f = 10pf 1v/div 50ns/div figure 6 - tsh151 hp3577a r3 = 10 w ,r4=1k w ,c f =0 30 /div 5db/div 100khz 1mhz 10mhz 100mhz -0 figure 7 - tsh150 frequency response changing the value of r3 from 1k w to 10 w gives a 40db amplifiying stage. note that for high gain, c f is now redundant since r3 is very small.the follow- ing wellknown curves show the frequency re- sponse, gain bandwidth product and phase margin for both devices (figure 7 and 8). one can observe the 47 o phase margin for 0db gain at 150mhz for the tsh150 and a 43 o phase margin for 0db gain at 80mhz for the tsh151 (markers). the gain bandwidth product of the tsh151 is specified at 7.5mhz with 26db of open loop gain. hp3577a r3 = 10 w ,r4 = 1k w ,c f =0 30 /div 5db/div 100khz 1mhz 10mhz 100mhz -0 figure 8 - tsh151 high speed buffer it can be seen in figure 7 and 8 that a good phase margin exists for both operational amplifiers with unity gain. therefore, it is possible to use them as followers for high speed buffer applications i.e. cable line drivers. shorting r4 and removing r3 technical note 3/4
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publication are subject to change without notice. this publ ication supersedes and replaces all infor mation previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectronics. ? the st logo is a trademark of stmicroelectronics ? 1999 stmicroelectronics printed in italy all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - france - germany - italy - japan - korea - malaysia - malta - mexico - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. ? http://www.st.com hp8160a + hp54100a r3 = ,r4=0 200mv/div 10ns/div figure 9 - tsh150 hp8160a + hp54100a r3 = ,r4=0 200mv/div 10ns/div figure 10 - tsh151 gives a follower configuration (a follower is the worst case in terms of circuit stability, since the sldb-001 pcb demoboard was not designed for this type of configuration and this results in a small oscillation when the tsh150 is used. to avoid these oscillations, the connection between the out- put and the inverting input must be direct and short). figures 9 and 10 show the response to a 20mhz 1vpp square wave. technical note 4/4
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