Q&A - Recent Threads

LTC6912 Input Current Chip Select Pin

hkmitto — Thu, 30 Jul 2026 14:15:35 GMT

I have an application where I use the LTC6912 as a multiplexing PGA (like p.24 of the datasheet), thus one channel of the device is active and one in software shutdown. There are four LTC6912 on my pcb in total for four independent channels,with their digital interfaces daisy-chained (like p.20).

Due to a design decision the chip select pin is driven via an open drain output with a pullup resistor. The datasheet makes no mention of the leakage current of the digital pins with the exception of the shutdown pin.

When using CH A with CH B in shutdown everything is fine with only up to 1µA leakage.

With the reverse setting though (CH B active and CH A in shutdown) the leakage current of the CS pin varies wildly from IC to IC with about 2µA and up to 54µA. These values where measured from tests with several ICs on several PCBs.

To make sure nothing else is interfering, we removed the open-drain output and pullup resistor from the circuit (thus only the CS pin is left) and drove the pin directly from logic supply (3.3V) with a multimeter in series to measure the current.

The values measured are also not in any way dependent on the actual gain setting of the active channel, only which channel is active and which in shutdown.

Temperature also did not seem to have any significant effect on the current.

The only difference, aside from which channel is active, is the daisy-chain output after programming. It is high in the first case and low in the second (which makes sense as that is the bit corresponding to the shutdown setting).

In my design this pin is only connected to the next amp or in case of the last amp nothing. I don't see how that should impact the CS pin leakage.

The Amplifier itself works fine in both cases, as long as the CS is pulled high properly.

My Questions are:

Why is there such a significant leakage in one configuration but not the other, which also varies a lot form IC to IC?

Can I get some kind of leakage specification for the CS pin, in order to choose a safe pullup resistor value?

Thanks in advance for any help that can be provided.

setting up a low corner for the OFST high-pass filter.

Rwolf01 — Fri, 03 Jul 2026 15:53:39 GMT

I'm trying to understand the reason for setting the HPF filter cap from OFST to CNTR rather than to ground. If Cntr is being driven by a low impedance Vref it shouldn't matter. Since they are both DC.

But your data sheet gives other options, like leaving CNTR floating and lightly bypassed. (eg 0.1uF in the eval board schematic, pg 29 of Rev H datasheet)

Now in the Offset Compensation section (pg 20, near eq 12) You suggest a 3.3uF Chp to get a 100 Hz corner. In that case the filter cap is 33x the bypass cap value, so it's clearly going to alter the performance.

Do you intend to feed a signal from OFST back into the CNTR pin in these cases? If so, you need to take the bias resistors and bypass caps on CNTR into account. Also, how would this work if CNTR was drive by a DC reference?

If you do NOT intend for OFST to feedback into and affect the CNTR voltage, why bypass to there instead of to ground? Also, how can your 3.3uF 100Hz cap possibly work?

In my application I'm targeting Vocm of ~ 1V and it seems I can hit that with a 2.67k R from CNTR to GND, with a suitable bypass cap in parallel to it. (0.1uF? 1uF?)

But I also want a HPF corner of 145 Hz, so eq 12 is telling me to use ~ 2.2uF But Eq 2 is only taking into account the internal 480 ohm Rint on OFST. In this case, it seems that OFST would be modulating the CNTR voltage and that the effective impedance of CNTR to GND would dramatically alter the corner frequency.

Am I thinking about this wrong, or did you just mess up the suggestions for low freq HPF in the data sheet?

Part number check

Pushkar — Thu, 04 Jun 2026 08:39:50 GMT

ADL6337ACRZB, is this the correct part number for this ADL6337-B? And what does this R7 mean in ADL6337ACRZB-R7

Operating limits

peteh — Thu, 23 Apr 2026 15:38:11 GMT

Hi. The AD604 data only specifies typical supply voltage: ±5V. What are min and max operating limits? Thanks.

Reverse Current Protection Not Working

Andy544 — Wed, 22 Apr 2026 11:56:46 GMT

I tested the IC by providing 5V to the IN and ON pins. The output is loaded with 400 mA and everything is working.

Then I externally drove the output to 5.2 V. Reverse current is flowing through the IC. It gets desaturated. In my opinion, this should not happen.

Does reverse current protection always work?

Greetings, Andy

Reference design for cascading all 4 channels in an AD8334 amplifier?

johntang — Thu, 16 Apr 2026 23:27:45 GMT

Hi,

A ~80dB VGA circuit that we have been using is literally two AD8331 EVAL circuits connected together, and I'm hoping to replace them with a single AD8334 with all 4 channels tied together to achieve similar result with less components.

Is it possible to connect the VOL1/VOH1 to VIN2/VIP2, then VOL2/VOH2 to VIN3/VIP3, VOL3/VOH3 to VIN4/VIP4 respectively, bypassing LNA2, 3, 4?

Is there a reference design out there that we could use?

Thank you!

Inquiry: Dynamic Envelope Shaping of a 350MHz Carrier using AD8367 V_gain Control

onyuhara — Wed, 11 Feb 2026 05:04:54 GMT

Hello,

I am designing a system to perform dynamic envelope shaping of an AM-modulated signal using the AD8367 in VGA mode. I would like to verify the feasibility of the following operation:

[Operational Scenario]

Input Signal: A 350MHz carrier with a 1MHz sine-wave amplitude envelope.
Goal: I want to "exaggerate" the envelope by driving the $V_GAIN$ with a 1MHz control signal that is perfectly phase-aligned with the input signal's envelope.
Desired Effect: By increasing the gain specifically at the peaks of the input envelope and decreasing it at the troughs, I aim to create a more "convex" or "peaked" output envelope compared to the input.

[Questions]

Feasibility of Dynamic Shaping: Is the AD8367 capable of performing this type of non-linear envelope scaling by varying the $V_GAIN$ voltage in real-time at a 1MHz rate? Are there any internal architectural reasons why the output might not follow the $V_GAIN$ modulation as intended?
$V_GAIN$ Bandwidth/Response: Does the $V_GAIN$ interface have sufficient small-signal bandwidth to accurately track a 1MHz modulation signal? Specifically, will there be significant distortion or "smearing" of the gain profile when the gain is updated every microsecond?

I am planning to calibrate the propagation delays manually through testing, but I would appreciate your confirmation on the fundamental capability of the AD8367 for this high-speed dynamic gain control application.

Best regards,

Unusually High Output Offset Voltage in AD8337 LTSPICE Model

govish87 — Fri, 19 Dec 2025 18:07:57 GMT

I'm planning on using the AD8337 VGA for a new design. When simulating the part, however, I noticed unexpectedly high output offset voltage present, seeming to disagree with quoted datasheet specifications.
The output offset voltage seems to be 50mV higher than expected, but the characteristic shape of the offset across gain setting seems to match.

I'm using Revision D of the SPICE model released in 2019 (the model currently posted on the website).

I've attached screenshots of my LTSPICE circuit and screenshots from the datasheet I'm referencing (pg. 22 of AD8337 datasheet). Notice the difference in output offset voltage between the simulation and the datasheet screenshot.

It seems like the SPICE model for this IC has historically had a lot of issues (though these seem to typically involve single-supply operation), see:

- AD8337 / SPICE MODEL Dynamic Range

- Simulation not working for certain values on the Vgain pin

- How can I correctly connect the AD8337 spice model?

- AD8337 supply

Please ensure the SPICE actually represents true device performance. Incorrect SPICE models make me hesitate to buy ADI products.

AD8338 stability issues

guimpt — Mon, 15 Dec 2025 16:39:53 GMT

Hello,

We are seeing a stability issue with the AD8338 VGA and would appreciate some guidance.

We are trying to amplify a ~500kHz signal from an antenna, the following is the circuit we are using:

(output is loaded by 2x470Ω resistors, oscillation persists even with no output load)

When gain is increased above ~50 dB, the output begins to oscillate at ~1–2 MHz. The input signal contains broadband noise, and it appears that noise peaks can momentarily overdrive the AD8338, after which the oscillation starts.

Could this behavior be related to the “Overdrive Recovery vs. Time” characteristic shown in the datasheet?

Are there recommended techniques to improve stability under brief overdrive conditions?

We can provide measurements or scope captures if needed.

Thank you!

AD8338 AGC Oscillation

Egecan — Wed, 03 Dec 2025 10:49:05 GMT

Hello! Below is the AGC circuit I designed for an AC coupled square wave input. I am using single-ended input thus connected INMR to the ground through C1. COMM and MODE are grounded. I have a bypass capacitor at VBAT and VAGC as well.

I have tested the circuit with VAGC = 2V and inputs of square wave 0.5-5MHz and the outputs OUTP and OUTM are oscillating. The output pins contain a 2.5MHz square wave for any given input. I have tried changing the VAGC values and the same output is observed for VAGC = 0.5-3V, below 0.5 and above 3V there is no output. Any idea what I am missing here? Thanks in advance!

Request of Gerber File for EVAL-AD8336

AkiraO — Thu, 27 Nov 2025 08:26:14 GMT

Hello,

Could you please provide me the design files or Gerber file of EVAL-AD8336?

Best Regards,

Akira

AD8338 VGA Mode no output

Akshay1992 — Tue, 11 Nov 2025 11:58:52 GMT

I am using AD8338 in VGA Mode. The given input is 10 kHz - 300 kHz, -40 dBm. Operating this circuit on DC 4.7V. When the Gain voltage is set to 0.8V, there is no output. The output came only after reducing the Gain voltage nearly 0.6V, which gives less than our desired gain, i.e., 60

What changes should be made to the schematic/PCB to achieve a Gain of 60 with an appropriate output?

Attached are the spectrum plot, the implemented schematic, and the fabricated PCB.

AD8338 VGA Mode, no output

JayeshU — Tue, 11 Nov 2025 05:24:15 GMT

This is regarding AD8338 I am using in VGA mode. The gain voltage set to 0.8 Volt. I am giving single input and taking single output. Deto pin Grounded. 0.1uF Capacitor connected between VREF and OFSN pins. 4.7V Power supply is given to the circuit.

200KHz, -40dBm signal is given as input.

With this configuration, I am not getting gain, no output.

Only I starts getting output when I slowly downs the gain voltage level from 0.8V to 0.6V. But, at this stage I am not getting my desired gain which is 60.

Pics and schematic is attached, What should be the change required to get desired gain of 60 with working output. My input range is 10Khz - 300KHz.

AD8330 LTspice simulation error

PARTH0076 — Tue, 19 Aug 2025 07:17:28 GMT

I am trying to build an AGC circuit with DC servo loop to keep my output AC signal around 0V. While simulating I get two errors

1- "Node U1:N662042 is floating and connected to current source G:U1:_G2"

2- Fatal Error: Analysis: Time step too small; initial timepoint: trouble with node "n007"

I downloaded the symbol of AD8330 from Analog devices website and changed the pins according to the datasheet.

ez.analog.com/.../Signal-generation-AGC-DC-servo.asc

Fabrication process

josei — Fri, 25 Jul 2025 19:55:08 GMT

Is the AD8336 fabricated using a SiGe bipolar process?

SPICE model of LTC6910-2

BDE — Thu, 24 Jul 2025 09:12:44 GMT

Hi,
I am looking for spice model of LTC6910-2 to be included in one of my simulations which is in PSpice for TI. I have located the .sub file for LTC6910-2 but I am unable to import it because of its encryption. It would really be helpful to share the spice model (.lib, .net, .cir) or IBIS model of this part.

Thanks and regards,
Ankit M

AD8338 no gain seen with ADA4940 at input and AD8130 at output

Akshay1992 — Tue, 08 Jul 2025 07:00:07 GMT

We have designed a separate PCB for evaluating the spurious response of the AD8338 in complete single-ended operation, utilizing the ADA4940 at the input for single-ended to differential conversion and the AD8130 at the output for differential to single-ended conversion. However, we do not see any gain; we are unable to understand what we miss.

Attached is the schematic for your reference. maaarmas GLADION can you through some light into this.

ez.analog.com/.../7288.DIFF_5F00_TO_5F00_-SINGLE_5F00_ENDED.pdf

AGC Spice simulation

dylanlouviaux — Fri, 06 Jun 2025 14:11:44 GMT

Does a spice model exist that has the AGC necessary pins so I can model an AGC circuit in LTspice?

What's the minimum operating frequency of LT5514?

PavelLevanov — Mon, 02 Jun 2025 14:56:34 GMT

Hello.

We are looking for this DGA LT5514 as baseband driver. Actually it's not clear from datasheet what's the minimum operating frequency for 1dB/3dB cutoff ?
It would be nice if you have a gain plot that starts from "DC".

Thank you in advance!

LTSpice simulation gain error for AD8336

Crom — Sat, 26 Apr 2025 15:43:02 GMT

Using the LTSpice model forAD8336 I checked gain using DC input vales to check gain values for my application (sensor inputs from ~-1v to ~ 5.5v at ~20MHz).

I modified the default circuit supplied by AD to add a DC input and measure input and output voltage.

I supplied DC values for GNEG and GPOS to try to get a gain close to 2x.

When I run with a 1V input I see a voltage gain of 2.0482

When I run with a 2V input I see a voltage gain of 2.2076

The simulation circuit is below

Do you see where I can fix this gain error? Or is there a defect in the model file?

Thanks,

Jambie

ADL5240 Replacement

RaySun — Fri, 21 Mar 2025 09:28:52 GMT

ADL5240 Last time buy.Could suggest the replacement parts?

Interface AD8331 with ADC AD9629

eRaju — Mon, 24 Feb 2025 09:32:02 GMT

I want to use AD8331 with AD9629 and regards to that I have prepared basic interface circuit as attached. Please refer it for the Vin connection of AD9629 to AD8331.

My concern is as below.

1> AD8331 having VCom is about 2.5 Volt as per data sheet and ADC AD9629 having V com 0.9 volt. I am using ac coupling between AD8331 and AD9629 so difference in Vcom ( I mean V com is not matching) So Is it ok or I need to select other ADC or ADC driver ?

2> As per Datasheet AD9629 it accepts 2V peak to peak and V Com is 0.9 so when we apply 2 V peak to Peak input voltage might be clipped on positive side by 0.1V (0.9 +1 =1.9) as the 1.8 AVDD for the ADC AD9629 and as well as for negative side it would go below 0V (0.9 - 1 Vin) by -0.1 volt so useful input Peak to peak voltage must be 1.8V not the 2 V peak to peak so please correct me If I am wrong. Datasheet of AD9629 says 2V peak is ok but It means it can tolerate 2V peak to peak input but AD9629 can produce fruitful result for 1.8 V peak to peak input so conform what is right.

ez.analog.com/.../Test_5F00_1.pdf

Simulation not working for certain values on the Vgain pin

sojhalb — Sat, 15 Feb 2025 01:47:09 GMT

I'm considering using the AD8337 in the design and would like to simulate the frequency response/bode plot. However when I set the Vgain to 0V or greater the simulations results show it acting as a big attenuator. For example when Vgain = -0.2V the circuit has around 8 dB of gain as expected. But when I test for Vgain = 0V or higher which is suppose to give higher gain than the circuit simulations fails and it has more than 200 dB of attenuation.

Thanks,

Sojhal

Setting VGA to maintain ADC input to a particular power

rahulpillai — Fri, 27 Dec 2024 04:13:48 GMT

How do i make it so that when the input signal is at or below -8dBm the VGA is set to 0dB and when the signal power increases it starts attenuating, so that the input to the ADC stays around -8dBm?

Several implmentation questions

Infraredx — Mon, 16 Dec 2024 15:50:46 GMT

Hello,

I have several questions on how to utilize this part properly. The overall scenario is an APD photodiode TIA circuit. The APD is first gained up by a MAX40213 TIA, with remaining gain provided by the AD8338.

1) The first design iteration was to use the AD8338 in a normal way providing 0-80dB gain. We unextpectly will be getting more gain from the APD itself, requiring the gain of the AD8338 be modified to be -20 dB -> +60 dB. There are instructions on how to do this on p.17 of the datasheet after equation (12), also pointing to Figure 43. The recommendation is to drive the INPD & INMD pins with 5K external resistances, and then short the INPR & INMR pins. Any reason why you couldn't just add resistors to the INPR & INMR pins and leave the INPD & INMD pins unconnected? Drawbacks to doing that?

2) On one of the other threads on AD8338 in EngineerZone someone asks what the transimpedance gain is if you use the AD8338 as a photodiode TIA directly. Advantages/disadvantages of doing that over using the MAX40213 first before the AD8338?

3) Just a nit - I think there is a typo in Equation (11). Shouldn't there be a log function after the 20x operating on the resistor calc in parentheses?