High Speed Amplifiers Forum - Recent Threads

OPA835

eli — Mon, 10 Jun 2013 17:58:26 GMT

Customer are using OPA835 with ±2.7V P/S.

need THD data. in DS there's no data for V_{OUT P-P} for above 2V_P-P.

please advise!

HIGH SDPEED AMP

eli — Tue, 23 Apr 2013 09:03:36 GMT

Looking for high speed, FDA amp. for 3,3V or 5V, to replace ADI, ADA4930, for ADC interface (ADS5402).

Need flat BW at 500M,with G=1 0r 2, and low distortion.

voltage to current converter

manu francis — Wed, 12 Jun 2013 04:45:58 GMT

Hi,

can anyone suggest high bandwidth ( upto 300 MHz) precision voltage( range from 0 - 5 V) to current converter?

Manu

NE5532P

ed meeks — Sun, 09 Jun 2013 03:01:41 GMT

Hello,

I am building a power supply and a demodulator for a turntable cartridge (strain gauge type) Both the power supply and the circuit have NE5532/OPA2604 opamps. One is a noise canceller for the power supply and the other is the signal amplfier chip. What models of these do you have that are the best you have? I am going to make a top notch unit so I want the part numbers for the cream of the crop.

I can provide schematics if you need them, to better get a sense of what the circuit(s) looks like.

high bandwidth op amp with same other feature as LM 741

manu francis — Thu, 06 Jun 2013 13:32:24 GMT

Hi,

I am trying to create an "auto balancing bridge" for impedance measurement in the range of 1 MHz to 10 MHz. For that purpose I need an op-amp . Can anyone suggest? I tried with LM 741 for low frequency,it is working properly. I tried with AD 8055 instead of LM 741 for high frequency impedance measurement, I am not getting any output.. Is any gain restriction for AD 8055 ? So I need an op amp with all same features except band width, need high band width upto some 300 MHz. ..

Regards ,

Manu

THS7373IPWR Theta JB

Jerry Chu61614 — Wed, 05 Jun 2013 09:47:06 GMT

Hi,

Where can I download THS7373IPWR thermal data? Thanks!

No of Pins: 14

Package Designator: IPW

Ambient Temperature: 25 C

Result- Theta JA-High K (standard datasheet value): 115

Result- Psi JT (standard datasheet value): ?

Result- Psi JB (standard datasheet value): ?

Result-Theta JC, top (standard datasheet value): 38

Result-Theta JB (standard datasheet value): ?

High output noise noise at the output of THS4271DGN non inverting buffer when feedback resistor=0E

Anoop Joshi — Tue, 04 Jun 2013 14:31:06 GMT

Hi,

I'm using a circuit which accepts a differential input through simple non inverting buffers and applies it to a Differential to Single ended converter(D2S) stage to obtain a single ended output. The schematic with the non inverting buffer section zoomed in is attached below.

The issue observed is that, the idle channel output, ie the output of the circuit with the inputs shorted to ground is observed to be very noisy. When checked with a digitizer with an inherent integrated idle channel noise of around -69dB, the integrated noise at the D2S circuit output comes to around -40dB. I'm sorry I couldn't attach an FFT plot to this mail, but it is seen that the noise floor itself goes real high. I could isolate the source of the noise and find that it was coming right at the output of the non inverting buffer. This is when the feedback resistor for the non inverting buffers were set as 0 ohms. When I checked with 250 ohms feedback resistors, it was observed that the output got totally clean, and I could measure some -68dB idle channel noise at the D2S output, very near to the digitizers inherent idle channel noise. I cannot really understand why the 0 ohms resistors caused the noise floor to worsen so much. I read in the datasheet that for unity gain configurations there are chances this op amp can show instability if the feedback resistance is 0 ohms, but that is supposed to happen at pretty high frequencies, ie around100MHz I believe. I'm doubting if it is due to some extra parasitic capacitance coming in the feedback path.. Can you please provide some insight into why 0 ohm resistance causes the noise floor to worsen for the non inverting buffer so much compared to say a 250 ohms resistance.A snap shot of the layout of the non inverting buffer section is given below: The hatched lines indicate cut out areas in the power and ground planes.

THS7353 - I2C issue solution step

Kawai — Wed, 20 Feb 2013 17:22:59 GMT

My customer is having THS7353 SDA line pulled low, cannot communicate with MCU.

I understand that THS7353 has an issue on I2C shown in the datasheet P.37, but, I cannot understand the solution steps.

Could you please tell me step by step ?

I am thinking as the following steps, am I correct?

1) Configure(Write) all channel registers of the device.

2) Send 1 SCL cycle => 1clk (1bit, data 0)

3) Send 8 SCL cycle => 8clk (8bit, data 0x00)

Best Regards,

Kawai

Problem with the amplifier THS4631 as an integrator

Gino Marceca — Mon, 20 May 2013 23:10:46 GMT

Hi, my name is Gino. I'm working on a circuit that is a Gated-Integrator that consist basically in three stages: An inverting amplificator, a sample and hold and a differential integrator. I'm using the FET amplifier THS4631 for all of these stages. The inverting amplificator is working well, but i am having problems with the sample and hold and with the integrator. The worst problem is that the integrator integrates a pulse but then, for a strange reason, the output is discharged and do not mainteing the voltage in the capacitor. It does not have any resistence in parallel so it should not do it. Something curious is that when I want to integrate a train of pulses, i can see that the velocity of the discharged increase from the first pulse to the last one. My objetive is to integrate at least 5 pulses of 1 ns width with a delayed of 1 ms per pulse maintaining the voltaje of each pulse, so it is imposible in these conditions. All these amplificators are supplied with a Vcc=+/- 14,84 V. Something strange that happens with the integrator too is that when i connect the negative input to ground, suddenly the output goes to +/- 13.53 V. Some occasions to a positive value and others to a negative. I think that i'm having two problems that are in essence one. The problem with the sample and hold is something similar but different. When the input is do not connected and i put on the supply voltage, the output and so the negative input, because it is a follower, goes slowly to - 13.53 V. It does not happen if i put the capacitor of the positive input in short circuit. I do not understand why i'm having these problems. I am glad to hearing from any answer.

Thanks!

Gino

single supply opamp or line driver

Mahendrakumar Reddy Ippagunta — Wed, 29 May 2013 11:37:49 GMT

We have 0.5V RMS audio signal that we need to scale up with 2X gain to feed aux-in of amplifiers. We have 3.3V switching supply and 4.2V linear available on the board. Can anyone help us in selecting the right chip that can do this. Can DRV612 line driver with 2X gain be used? or we need to choose an op-amp? If opamp, what are the suitable opamps from TI that operate with the available single supply of 3.3V switching or 4.2V linear.

-Mahendra

OPA2836 oscillation issue

Nikhil Tiwari — Wed, 29 May 2013 16:19:36 GMT

Hi,

We are using OPA2836 ICs on our board to support P and N lines for a differential pair. On the board after there are two paths TX and RX and at end of TX path and starting of RX path this IC is used in unity gain configuration. it has output pin shorted to negative input pin. when we do a loop back i.e. connect the output from IC in TX directly to positive input pin of other IC in RX path the output of TX Op-amps start oscillating. and the oscillation is same in amplitude as well as frequency for both P and N op-amps. Is this because of some specific requirements of OP2836 that are not met?? if we don't connect the output to input of other IC then both the devices work fine. Please help.

Thanks and regards,

Nikhil

OPA836 linear output range question

Gerard Visser — Fri, 24 May 2013 01:55:54 GMT

I note two facts about the OPA836:

- The output range is only specified in the datasheet at a gain of +5

- The PSPICE simulation of an inverting amplifier at low gains seems to show saturation effects well within the datasheet linear range (0.2 to 4.75 at 5V supply). [In particular, I am looking at G = -1.65, VCC = 5V, Vin+ = 2.728V, Rf=1.65k, Rg=1k, Vsource=4.238 V +Vac, then the output AC gain is less than expected 1.65,]

My real question is, is the datasheet guaranteed linear output range spec actually something I can count on at an inverting gain of 1 or a bit more??? Or is there some kind of intermediate-stage signal swing limitation in the OPA836 that I need to worry about.

Of course, I will build a prototype and see. SPICE is just for picking the general form of the circuit and which parts to use. But, I'd like to have some more confidence that I am going in the right direction by picking the OPA836.

If anybody can confirm the 0.2 to 4.75V output range for 5V supply with G=-1 (or a bit more like I need), I would appreciate to hear from you. Thanks!

[p.s. In case you are wondering about the DC bias point mentioned above, this is for a unipolar pulse application.]

opa642 replacement

tim camarda — Fri, 24 May 2013 17:31:05 GMT

Hi,

I believe somewhere that TI had a recommended replacement for the OPA642.

Cant seem to find this. Any help is appreciated.

Tim

OPAx355 Common Mode Range Behavior

Paul Bryson — Fri, 24 May 2013 18:01:52 GMT

What is the behavior of the OPAx355 amps when the common mode input range is exceeded, assuming that the rails are not exceeded?

Does the output undergo phase reversal?

Is the input impedance compromised?

Long line video driver

Neil McNeil — Sat, 18 May 2013 00:13:17 GMT

I have the need to drive a PAL video signal up 1000M of RG59 Co-Ax cable with the appropriate frequency compensation.

I have been looking at the OPA 693 for experimentation but I will require some extra gain other than the x2 offered by this device.

This is obviously a big ask, but absolute fidelity is not required, just a good useable image - any suggestions welcome.

Regards

Neil

Lower operational voltage supply limit for LMH6702.

J��rn Pedersen — Tue, 21 May 2013 11:36:46 GMT

I am trying to drive the 50 ohms balanced inputs of the ADC12D1800 ADC without damaging the inputs. This means not more than 2.5 Vpp.

I am thinking of making a differential output using the LMH6702, but it is specified to only +/- 5 V supply. For how low supply voltages will it operate properly. I need a bandwith of appx 800 MHz.

Jørn Pedersen

About PSRR of LMH6518

Zheng Zhao — Sat, 18 May 2013 15:14:39 GMT

It shocked me that the psrr of lmh6518 is negative...

So it means a power supply with ripple of 1mv will cause an output with 1000mv ripple?????terrible...

But it defines the PSRR below , while i don't understand...

Or the changes is only in CM voltage?? not differential?

LMH6522 EVAL PCB layout

Victor Verzilov — Thu, 09 May 2013 17:05:08 GMT

Hello,

I have a problem with managing heat dissipation using LMH6522. My board has 6 layers and is as nearly as big as LMH6522 evaluation board.

However my board gets very hot whilst the evaluation board stays reasonably cool. Is there a chance I can get the evaluation board PCB layout?

Thanks you in advance.

OPA835 output impedance

Vinson Go — Tue, 14 May 2013 23:42:44 GMT

For the OPA835, the data sheet shows that the output impedance goes high when the op amp goes into power down mode. If the power is disconnected, does the output impedance also goes high?

Comparator Based Peak Detecting

Jason Amis — Fri, 17 May 2013 17:51:01 GMT

I'm trying to Peak detect a signal that varies from 5 kHz to 5 MHz. One of the circuits I've come across with the most promise uses a high speed comparator (See below). My problem lies in the fact that there is no high speed comparator with a nice low input offset voltage, and generating a calibrated high speed sine wave isn't exactly easy. I'm curious if anyone has an idea for an easy fix to this problem. Also seems like an idea to pass along to your product development guys.

Suitable feedback network for THS 4503 with SE unipolar signal input

mariano rotunno — Tue, 09 Apr 2013 22:01:09 GMT

Hi all,

i really appreciate if you could suggest me a suitable feedback network with Rf Rg Rt resistor values to make it possible to read an unipolar SE signal that

swings between 0 and +15V range in a way to remap this input to differential output respectively -3V to +3V (Vdiff=(Vout+) - (Vout-)).

I need this to take advantage of the ADS1675 maximum input range that is precisely ±3V.

The input signal is exactly a pulses train that have variable height between 0 and 15VDC.

Also have you inherent documents that show how to perform calculation for this particular case with fully differential amplifiers ?

Thanks in advance.

Voltage follwer

Tony Brown — Tue, 14 May 2013 13:11:07 GMT

I am looking at to parts to make a voltage follower. They are TLE2037 and LM318M. The problem comes when I build them up according to the data sheet, I immediate have noise on the output once I turn on power but don't have an input signal. What am I doing wrong? The supply voltage is 12V DC.

THS4520 Spice Model in Harmonic Balance Simulation

Markus HighSpeed — Wed, 15 May 2013 16:53:11 GMT

Hi,

I tried to use the THS4520 spice model in a harmonic balance simulation but it does not converge. The circuit itself seems to be stable and works fine with transient and ac simulations. It also works with harmonic balance simulation using the THS4509. Trying a lot of different constellations, the THS4520 spice model seems to produce the problems.

Are there any known issues using the THS4520 spice model in harmonic balance simulations?
Any suggestions to improve the behavior?

Thanks,
Markus

LF411C

Kumiko Sejima-Woods — Tue, 14 May 2013 16:40:33 GMT

Hello,

I have downloaded the Pspice model for the LF411C and created its symbol. When I try to simulate the circuit, I get the error saying that Pin1 through Pin5 are

not in the template. The subckt has the pins from 1 through 5 and without knowing which pins correspond to which pins in the datasheet, the simulation will

fail. I think that's what's happening. This is a 7-pin device. I thought that the two missing pins are the power pins., so I assigned the pins

and added twp power pins in the symbol. It didn't work. I think that the "Order" in the part property is messed up. I don't want to spend time to try assingning

different ways. Does anyone have the correct part property that correspond to the subckt for LF411C?

Thank you,

THS3202 model isn't working.

Sergio Montero — Tue, 14 May 2013 16:17:36 GMT

Hello,

I'm using Altium in order to simulate this simple G = 2 non-inverting amplifier (the same that can be found in TSH3202EVM):

The output of the circuit above is this:

As can be seen, the output has 1 mVpp when the input is 60mVpp. This makes no sense. I'm using this simulation file:

* [Disclaimer] (C) Copyright 2003 Texas Instruments Incorporated. All rights
* reserved.
*
* Texas Instruments Incorporated hereby grants the user of this SPICE
* Macro-model a non-exclusive, nontransferable license to use this SPICE
* Macro-model under the following terms:
*
* Before using this SPICE Macro-model, the user should read this license. If
* the user does not accept these terms, the SPICE Macro-model should be
* returned to Texas Instruments within 30 days.
*
* The user is granted this license only to use the SPICE Macro-model and is
* not granted rights to sell, load, rent, lease or license the SPICE
* Macro-model in whole or in part, or in modified form to anyone other than
* user.
*
* User may modify the SPICE Macro-model to suit its specific applications but
* rights to derivative works and such modifications shall belong to Texas
* Instruments.
*
* This SPICE Macro-model is provided on an "AS IS" basis and Texas Instruments
* makes absolutely no warranty with respect to the information contained
* herein.
*
* TEXAS INSTRUMENTS DISCLAIMS AND CUSTOMER WAIVES ALL WARRANTIES, EXPRESS OR
* IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
* PURPOSE. The entire risk as to quality and performance is with the Customer.
*
* ACCORDINGLY, IN NO EVENT SHALL THE COMPANY BE LIABLE FOR ANY DAMAGES,
* WHETHER IN CONTRACT OR TORT,INCLUDING ANY LOST PROFITS OR OTHER INCIDENTAL,
* CONSEQUENTIAL, EXEMPLARY, OR PUNITIVE DAMAGES ARISING OUT OF THE USE OR
* APPLICATION OF THE SPICE Macro-model provided in this package.
*
* Further, Texas Instruments reserves the right to discontinue or make changes
* without notice to any product herein to improve reliability, function, or
* design.
*
* Texas Instruments does not convey any license under patent rights or any
* other intellectual property rights, including those of third parties.

*
*$
.subckt ths3202 inp inn out vcc vee
*
.MODEL D_break D
+ RS=1.0000E-1
+ CJO=1.0000E-13
+ IS=100e-15

.MODEL pnp_is PNP
+ IS=10.000E-18
+ BF=124.36
+ VAF=100
+ IKF=.99789
+ ISE=10.000E-18
+ NE=1.3695
+ VAR=100
+ IKR=10.000E-3
+ ISC=10.000E-18
+ NK=1.8752
+ RE=1
+ RB=80
+ RC=10
+ CJE=12.000E-15
+ VJE=.9
+ MJE=.6
+ CJC=10.000E-15
+ MJC=.93
+ TF=8.0237E-12
+ XTF=12.990
+ VTF=12.704
+ ITF=.88449
+ TR=10.000E-9
+ KF=7e-14
+ AF=0.54
.MODEL npn_is NPN
+ IS=10.000E-18
+ BF=205.81
+ VAF=100
+ IKF=.99979
+ ISE=19.329E-18
+ NE=1.6102
+ VAR=100
+ IKR=20.000E-3
+ ISC=10.000E-18
+ NK=1.8762
+ RE=1
+ RB=100
+ RC=10
+ CJE=16.000E-15
+ VJE=1
+ MJE=.4
+ CJC=1.6000E-15
+ TF=5.5979E-12
+ XTF=97.940
+ VTF=28.359
+ ITF=2.2510
+ TR=10.000E-9
+ AF=0.54
+ KF=10.5e-14
.MODEL my_d D
+ IS=10.000E-18
+ RS=1.0000E-3
+ CJO=1.0000E-12
+ M=.3333
+ VJ=.75
+ ISR=100.00E-12
+ BV=100
+ IBV=100.00E-6
+ TT=5.0000E-9

* source THS3202
Q_Q1 VCC INP1 N00790 NPN_IS 32
R_R7 N03087 VCC 10
D_D2 N031571 N025972 MY_D 64
E_E4 N16469 N16504 0 N16382 1
Q_Q2 VEE INP1 N00761 PNP_IS 64
R_R8 VEE N03033 10
V_V9 N19555 VEE 1.3Vdc
**V_V2 HIZ N02762 -4.3Vdc
Q_Q5 N01212 N01212 A1 PNP_IS 32
L_L3 N03266 OUT 2.1n
V_V8 N19322 VCC -1.3Vdc
R_R21 0 N16008 123
R_R9 N03266 N031180 8.5
*R_R11 0 OUT 100
C_C1 eref HIZ 430f
R_R1 A1 A 200
R_R13 0 N09161 10
C_C6 0 N16008 1p
Q_Q7 N01642 N01642 B1 NPN_IS 32
C_C3 N09161 INN 700f
R_R10 N031571 N03266 8.5
G_G1 INN_int 0 N15578 0 4m
R_R3 B B1 200
C_C2 0 OUT 1p
R_R2 eref HIZ 300k
Q_Q3 N01212 N00761 INN_int NPN_IS 32
V_V7 INP N26257 -17mVdc
X_U6 B VEE HIZ VEE CSWIL PARAMS: IL=3000U
R_R22 N16382 0 1.4k
R_R20 0 N15578 1k
Q_Q4 N01642 N00790 INN_int PNP_IS 64
C_C7 N16382 0 700p
I_I1 VCC N00761 DC 325uAdc
E_E1 N03087 N025673 N02649 eref -1
L_L4 INN INN_int 1.15n
I_I2 N00790 VEE DC 325uAdc
L_L7 N25506 N16504 0.2n
D_D7 N19555 HIZ D_BREAK
E_E2 N025972 N03033 N02762 eref 1
R_R28 N26257 N25506 -49.8u
**V_V1 HIZ N02649 4.3Vdc
D_D1 N025673 N031180 MY_D 64
C_C5 0 N15578 1f
X_U5 VCC A VCC HIZ CSWIL PARAMS: IL=3000U
C_C8 0 N16504 10f
D_D6 HIZ N19322 D_BREAK
E_E3 INP1 N16469 N16008 0 1
E_E101 avg vee vcc vee 0.5
E_E102 eref 0 avg 0 1
E_E103 diff 0 vcc vee 0.5
E_E104 lshift 0 diff ddrop 1
V_V102 ddrop 0 0.7
E_E105 HIZ N02649 lshift 0 1
E_E106 HIZ N02762 lshift 0 -1

.ENDs ths3202
*$

.SUBCKT cswil 1 2 3 4
+ PARAMS:
+ IL = 800u ;
v1 1 2 0
Gout 3 4 value={limit(I(v1),IL,-IL)} ;
.ENDS cswil

Can anyone help me?