AD8302: Offsetting the phase output

Question With AD8302, is there a simple circuit layout that lets me offset phase detection response? For example, I'd like to have maximum value, 1.8V, when phase difference is -45 degrees, avoiding to use a phase shifter on inputs. Answer It is definitely a better idea to do the offsetting at the output rather than trying to manipulate the phase at the RF input. The section entitled "Modulating Slope and centre point" on page 18 of the datasheet(RevA) shows you how to modify the offset and gain of both the magnitude and phase outputs. You may also figure 3 on page 16 of the datasheet instructive in understanding the Magnitude and Phase output interfaces. Looking at figure 5 of the datasheet which shows the Idealized transfer characteristic, you can see that you can have 1.8V occurring at -45deg by modifying the gain and offset.

AD8302: VPHS output changes with different input signal amplitude

Question There is a question about AD8302 as below. I connect the node 1 and node 2 with VINA and VINB as below. When I changed the amplitude of input signal V1, the output of VPHS will change too. When V1=120mV, VPHS=1.79V; When V1=10mV, VPHS=1.26V. Actually, the phase did not change with the amplitude of V1, the VPHS should not be changed. Would you kindly give some professional suggestions on this issue? BTW, the output of VMAG is always correct. Answer Please increase the value of the filter caps and the input caps as they are not suited for such low frequencies. Page 13 of the AN-691 application note " Operation of RF Detector Products at Low Frequency" discusses low frequency operation of the AD8302. The shift is coming through the cap to gnd. Please see Figure 1 in the attachment.

AD8302: Hot to measure +/- 180deg phase

Question I am interested in a build a Vector Network Analyzer but AD8302 can only detect +-90 degrees. To make a good Vector Network Analyzer its not necessary to detect +-180 degrees? Answer IN fact the AD8302 allows you to measure 0 to 180deg phase but there is no simple way to determine direction of phase. One possibility is to temporarily insert a known phase shift into one of the signal paths and then observe the way in which the VPHS output changes. When slope of the VPHS output is determined, then one can determine in which quadrant the angle lies. For narrow band applications (which obviously does not describe this application) two AD8302's can be used. The INPA's for each of the AD8302's are connected to the same signal, via transmission lines of equal electrical length. One of the INPB inputs is connected to the other signal of interest. The second INPB is connected to the same signal, but via a transmission line that is 90 degrees linger. Then, the VPHS outputs can be compared to each other to determine the phase angle anywhere between 0 and 360 degrees.

AD8302 evaluation board information

Question Does any information about the eval board AD8302-EVALZ exist? Beside the Gerber Files. Answer You should find a lot of eval board stuff on page 21 of the AD8302 datasheet rev. A. Also, attached are the schematic, .brd file, and BOM.

AD8302 Full phase detection

Question I have purchased an AD8302 evaluation board and am looking to use it to detect a phase difference of the incoming signals. Is it possible to tell the difference between a positive and negative phase difference as as far as I can see they will both always give the same voltage. Answer Attached is one way of detecting positive or negative phase difference: basically using two AD8302's to make a 360 degree phase detector. Another way to do it is with an IQ demodulator (also attached).

AD8302 spice model and gerbers for eval board

Question AD8302 spice model and gerbers for eval board: Do you provide details suitable for "Proteus/ISIS7 professional pcb package", including a spice model which can be used for simulations ? If so can I download the data please? Or is there any documentation for the eval board? Answer Unfortunately no models are available for the AD8302. Please find attached the board .brd and gerber files for the eval board.

The permittivity and the thickness of the AD8302’s EVB.

Question I wonder some details of Evaluation Board of AD8302. I want to know the permittivity and the thickness of the AD8302’s EVB. Could you please help with the issue? Answer The EVB is a 4 layer board. The target thickness for the first dielectric layer is 8.33 mils. The next dielectric is 39 mils, the 3rd dielectric is 8.33 mils. Layer 1 & 4 are ½ oz copper and layer 2 & 3 are 1 oz copper. The finished board thickness is 62 mils. The 50 ohm line width are 16 mils. The dielectric constant is 4.2. The first and third dielectric material are IS410. (higher temp version of FR4) The second dielectric material is FR4.

AD8302's Small Signal Envelope Bandwidth

Question I am not sure about "Small Signal Envelope Bandwidth" mentioned in the section of SPECIFICATIONS. Would you please help explain below parameter? Answer the small signal bandwidth is essentially the bandwidth of the device's output stage. If you have two steady state (i.e. constant power) input signals going into the two inputs, you will get a dc output proportional to the input power difference. Now, if one of the inputs has an input level which is changing, the output will respond to this change. The bandwidth spec tells you how fast the output can respond to input signal changes at one or both of the inputs.

AD8302 Gain/Phase Detector: Operation as a Frequency Discriminator

Q. Can the AD8302 gain/phase detector be used as a frequency discriminator? ----------------------------------------------------------------------------------------------------------------- A. If two signals of different frequencies are applied to the inputs of the AD8302, the output will be a triangle wave; similar to that shown in the TPC section of the data sheet (TPC’s 25-29; indeed, this is how these plots are generated). The frequency of this triangle-wave signal is equal to the frequency difference between the two input signals. The limit to the AD8302’s ability to determine the frequency difference is determined by the envelope bandwidth of the device. The envelope bandwidth is set by the capacitor on the PFLT pin.

AD8302 Gain and Phase with no Input Signal

Q. What is the output voltage of the AD8302 gain/phase detector when there are no signals present on the inputs? --------------------------------------------------------------------------- A. With no input signal, the AD8302 compares the noise on the two inputs. The noise on the input is generally the same level, so the magnitude output is approximately 0.9V. Due to an internal 90 deg phase shift, the Phase output is also approximately 0.9V.

How can I avoid startup transients when operating the AD8318 in Controller Mode?

Q. How can I avoid startup transients when operating the AD8318 in Controller Mode? I am using the AD8318 Log Detector/Controller to control the output level in an AGC loop. The control loop consists of a fixed-gain RF amplifier, an ADL5330 VGA, and the AD8318 Log Amp. The circuit is similar to Figure 37 on Page 16 of the ADL5330 data sheet, except with the fixed gain amplifier inserted after the ADL5330 VGA. I am seeing a startup transient at the output of the RF amplifier. During startup, the detector is seeing no signal at the amplifier output. This causes the VGA go max gain, producing the transient at the RF amplifier output that is present until the loop settles. Is it ok to short the CLPF pin to ground during startup to prevent this transient? -------------------------------------------------------------------------------------------------------------- A. The CLPF node is internally fed by a current mirror. By connecting the CLPF node directly to ground, overtime a transistor in this circuit will degrade and eventually fail. The problem is the Vbceo of the transistor is exceeded. A better solution to minimize the transient during the power up sequence is to force the VGA to minimum gain. During initialization, enable / disable the circuit using the enable pin on the ADL5330. Before enabling the VGA bring the VSET voltage on the AD8318 to 2.5 V. This translates to a power level well below the minimum detectable power of the AD8318. As a result the gain of the ADL5330 will be set to its minimum eliminating the severe overshoot.

AD8302 Gain/Phase Detector, Response to Modulated Signals

Q. How does the AD8302 gain/phase detector respond when it is driven by signals such as a modulated carrier whose phase is changing continuously? ----------------------------------------------------------------------------------- A. The AD8302 does not need to be driven by two fixed-phase signals to produce a valid output. The device AD8302 works just as well when driven by modulated carriers whose amplitude and phase are continuously changing.