OPA863: Envelope detection of the NFC signal

Hello Danilo,

Good question!  Peak detection is a use-case for clamping circuits containing op-amps with diodes, also known as 'DC restore' or 'DC restoration' circuits.  Beginning with brevity, the -VBias voltage present in Fig. 9-3 'clamps' or 'restores DC' to the signal by shifting the AC signal around a bias voltage.  For the particular high-speed peak detector, the clamping behavior is set by the two diodes & VBias.

While you may have your own references or knowledge on Peak Detection, there are some TI resources and parts which contain a more description on the topic:

https://www.ti.com/lit/ug/tidu155a/tidu155a.pdf

The OPA615 and OPA860 are DC Restoration ICs from HSAMPs which have explanations in their datasheets.  There is likely additional TI material on 'DC Restoration' on ti.com, as well as other envelope & peak detection resources.  The following two past e2e posts also discuss this:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/617440/envelope-detector

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/550168/envelope-amplifier

Regarding the capability of the circuit in Fig. 9-3, it does appear your application bandwidth is contained inside the recommended operating conditions of the OPAx863 device.

Please look over these resources and respond with any additional questions you may have.

Best,

Alec

Hi Danilo,

the circuit is not very precise but should work:

danilo_opa863.TSC

Kai

Hi Alec and Kai,

Please an earlier response of our customer below before Kai's message.

Thank you for your generous response to my inquiry.

Looking into your suggestions, I would first like to explain the purpose for choosing OPA863. 

- I am planning to detect a 13.56 MHz signal with varying amplitude (for example the varying information signal might be the human pulse or sth like that).  Since my input power is limited (+3.3 V), I am considering to utilize the single supply mode of the proposed op-amp.

- OPA2863 also has two op-amps which can be used for bandpass filtering of the carrier signal and active peak detection as shown in Fig. 9-3 of the datasheet, which reduces the overall chip area compared to OPA615.

- Another consideration would be like my carrier signal amplitude is too high (ca. +- 15V), which need to be suppressed before passing to the op-amp operating mode.

For all requirements, I would be grateful to you, if you could give me some insightful comments and circuit suggestions.

Regards,

Danilo

Hi Team, 

Please see the response of our customer below.

As Kai mentioned with the circuit, I am curious if there are any alternative circuits with more precision to fit my purpose with frequency, voltage considerations?  

Regards,

Danilo

Hello Danilo,

I see from your response you intended to share customer feedback; is the following phrase the full summary of the customer's response:

"As Kai mentioned with the circuit, I am curious if there are any alternative circuits with more precision to fit my purpose with frequency, voltage considerations?  "

Does your customer have any values or metrics for their desired precision?  Could you reiterate your frequency & voltage considerations as well, especially if they have changed?

Best,

Alec

Hi Alec,

According to our customer,

I would prefer to obtain a sensitivity of about 50mV meaning that the change in input carrier voltage amplitude by 50mV should be reflected in the output envelope. 

Regards,

Danilo

Hello Danilo,

Thank you for clarifying the target performance; can you share the sensitivity level or related performance you have been able to simulate/design so far?  I am not sure if you were using Kai's circuit as a starting point or setting up simulations from circuitry described in Sima's references.

Best,

Alec