Product Description
The Mixed-signal processing card, which adopts the Xilinx ZYNQ UltraScale+ RFSoC ZU27DR as part of its Digital-Analog Hybrid Systems, provides access to large FPGA gate density, 2-channel ADC/DAC ports, expandable I/O ports, and DDR4 memory. It is suitable for various programmable applications. Equipped with the ZU47DR FPGA, the 2T2R supports 2 channels of 12-bit, 4.0 GSPS ADC, and 2 channels of 14-bit, 6.554 GSPS DAC ports.
Interwiser RF transmit and RF receive ports are connected externally via high-performance SMA side-mounted RF connectors. The ZYNQ UltraScale+ RFSoC serves as the core processing system, featuring a rich set of peripheral interfaces for matching peripheral control signal transmission in signal processing. IW-RFSOC-2T2R board features a 40Gbps QSFP connector providing a 10Gbps SFP optical interface, capable of efficiently handling high-speed data in parallel with analog and digital conversion. The PS and PL are respectively equipped with 4GB DDR4 and 2GB DDR4 memory. It supports Micro SD card (supports UHS), 10/100/ Ethernet, USB JTAG/UART&#;and the board's JTAG loading mode shares the UART output, a RS232 interface&#;a GPS module&#;and a GPIO expansion interface for functional extensions.
Key Technical Parameters
:
FPGA Chip
Zynq UltraScale +XCZU27DR-2FFVEI
RF Interface
X 2 ADC (12-bit, 4.096GSPS) ports
X 2 DAC (14-bit, 6.554GSPS) port s
Frequency range: DC-4GHz
Interface Rate
4 0G(1 piece)
Memory
PS 4xDDR4(4GB,64bit,2 666 MT/s)
PL 2xDDR4 ( 2 GB, 32 bit, MT/s)
Board power supply
Commonly used 2.5mm round head power socket ( DC+12V)
Size
180mm *135mm
Environmental temperature requirement
Working temperature -40&#;~110&#;
PS Port
2 xQSPI flash (512MB, 8bit) fixed configuration files
1x 10/100/ Ethernet RGMII (RJ45) port
1x USB_JTA2xG/UART debug interface
1x JTAG debug interface
1x Micro SD Card
If you are looking for more details, kindly visit interwiser.
PL Interface
2 -channel ADC (12-bit, 4.096GSPS) ports
2 -channel DAC (14-bit, 6.554GSPS) ports
1 X QSFP+ 40G optical port
1 XSFP+ 10G optical port
1- way I2C interface EEPROM
1 GPIO interface (interface type: side-inserted SMA connector )
GPS interface (interface type: side-inserted SMA connector)
1 SPI interface and 1 GPIO ( interface type: J30J connector )
36 XGPIOs ( interface type: 2.0 mm pitch curved socket)
1 XRS232 interface (interface type: 2.0 mm pitch curved socket)
8 XLEDs
The cold multiplexing system depicted in Fig. 1 encodes the detector signals into phase and amplitude of the probing tones. Therefore, the noise present at these coordinates is indistinguishable from the detected signals [16]. The scope of this work is to quantify the noise degradation due to the SDR system with respect to the cryogenic low-noise amplifier (LNA) noise within the range of possible frequencies adopted by the flux-ramp modulation for bolometric applications and assuming a phase domain readout [17, 18].
First, the signal generation performance was characterized seeking to ensure the quality of the tones required for monitoring the \(\mu\)MUX channels. For this, a number of N = 200 tones centered at 7.5 GHz were generated with a Gaussian frequency distribution with \(\mu =4\) MHz spacing and \(\sigma =200\) kHz deviation. This emulates the resonance frequency distribution of a real multiplexer given by variations in the manufacturing process and allows for the identification of inter-modulation products generated within the readout bandwidth. Comb generation was performed by continuously reproducing the complex waveform stored in Block RAM (BRAM) at a rate of 1 GSPS by the DACs. It has a memory depth of \(2^{17}\) complex samples resulting in a frequency resolution of \(\Delta f\approx 7.6\) kHz which is sufficient for frequency placement in bolometric applications where the resonator bandwidth is BW\(\approx\)200 kHz [4]. Then, the base-band signal was up-converted to 7.5 GHz by the RF-mixing board. Figure 2 shows the generated frequency comb at the RF-mixing board transmitter output (Tx). The selected tone power at Tx port is &#;40 dBm considering an optimum readout power of &#;75 dBm at the \(\mu\)MUX input port and 35 dB of cold attenuation [19]. In order to utilize the DACs dynamic range efficiently, several Peak-to-Average Power Ratio (PAPR) minimization methods were evaluated [20], but none of them performed significantly better than the random phases method with an average PAPR \(\approx\) 12 dB in case of nonuniformly spaced tones.
Fig. 2Power spectrum of 200 fixed tones generated by the RFSoC-based SDR system proposed in this work using random frequency spacing (\(\mu =4\) MHz spacing and \(\sigma =200\) kHz deviation) centered at 7.5 GHz with -40 dBm power per tone. The inset shows a close-in-look at one tone taken as example to see the close-in spurious signals produced by the SDR system
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The transmitter output (Tx) was connected to a R &S FSWP50 phase noise analyzer, where six reference tones were measured regarding their phase noise. This selected subset is representative of the quality of all generated tones. The results of these measurements are presented in Fig. 3. The shaded green region represents the frequency band where the detector signal flux-ramp modulation will be typically between 10 and 100 kHz for bolometric applications [4, 6]. The dashed cyan line represents the phase noise present in the local oscillator of the RF-mixing board without tone generation. It can be seen that this local oscillator imposes the shape of the stimulation phase noise. The phase noise profile in the band of interest is dominated by Voltage-Controlled Oscillator (VCO) white phase noise and spurious signals, while the quantization noise is negligible. This value is compared with the estimated cryogenic LNA noise level represented in the dashed black line in Fig. 3. LNA Single-Sideband (SSB) phase noise \({\mathscr {L}}(f)\) can be calculated according to [21]
$$\begin{aligned} {\mathscr {L}}(f)=\frac{k_BT_n}{2 |S_{21}^{min}|^2 P_{r}} \end{aligned}$$
(1)
where \(k_B\) is the Boltzmann constant, \(T_n\) is the LNA equivalent noise temperature, \(S_{21}^{min}\) is the resonance depth and \(P_r\) the tone power at µMUX input. Assuming an LNA equivalent noise temperature of \(T_{n}\approx 4\) K, resonance depth of \(S_{21}^{min} \equiv -15\) dB and \(P_r\approx -75\) dBm as mentioned earlier, the minimum Single-Sideband (SSB) phase noise density at the multiplexer output is \({\mathscr {L}}(f)\approx\) -106 dBc/Hz. Therefore, a maximum degradation of 3 dB with respect to the contribution of the cryogenic LNA is expected due to the phase noise present in the probing tones.
Fig. 3SSB phase noise for selected tones at transmitter output (Tx). Green and black dashed lines are the up-conversion local oscillator and cryogenic low-noise amplifier phase noise profiles, respectively. The shaded green region represents the possible region for flux-ramp modulation (FRM) frequencies
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Later, once the spectral purity of the generated tones had been characterized, we evaluated the degradation of the tones due to the receiver path. A loop between the transmitter (Tx) and receiver (Rx) ports of the RF-mixing board was created through a \(\approx\) 10-m-long cable with around 15 dB attenuation, emulating the typical input&#;output attenuation of the cryogenic RF circuit at resonance [5, 22]. This is consistent with 15 dB of net attenuation resulting from the combination of 35 dB of cold attenuation, a typical LNA gain of 35 dB and &#;15 dB resonance depth. Considering that the tones were generated with random phases and the fact that in a real measurement both the RF components and the detector signals will lead to a pseudo-randomization of the phases, a PARP \(\approx\) 12 dB at the input of the ADCs was considered. Hence, the attenuation of the Rx path was adjusted to satisfy \(P_{tone}\approx -40\) dBFS for optimum ADC SFDR.
On the receiver side, the frequency comb was amplified, down-converted to base-band, and filtered by the RF-mixing board. Then, in the digital domain, the tones were channelized, down-converted, and filtered again. The IQ data streams of each channel were acquired, and the SSB phase noise density \({\mathscr {L}}(f)\) was calculated. Figure 4 shows the phase noise of the same six reference tones measured in the previous step, but after being processed by the receiving chain. A detailed analysis shows that the 1/f phase noise component was almost completely removed during down-conversion and sampling process, except at frequencies below 10 Hz. This is consistent with the fact that all oscillators and clocks are locked to the same frequency reference maintaining strong coherence between transmitter and receiver for frequencies below 10 kHz. Beyond our application, which is not sensitive to low-frequency noise, the noise below 10 Hz is being studied because of its importance for the readout of other types of detectors such as MKIDs [22]. In the case of frequencies above 1 MHz the roll-off on the noise profile is due to the combination of the channelizer and a 1,6-MHz Digital Down-Converter (DDC) low-pass filter, while the phase noise plateau above 5 MHz around &#;136 dBc/Hz is consistent with the theoretical predictions for quantization noise. Within the band of interest, the noise profiles are dominated by the white-phase noise component and several spurious signals. The black dashed line in Fig. 4 corresponds to the average white phase noise of &#;102 dBc/Hz and represents a degradation of less than 6 dB with respect to the noise level present in the injected tones. The white phase noise component is a combination of the phase noise present in the injected tones and the thermal noise added by the RF-mixing board, while the spurious signals are mostly inter-modulation products produced by the nonlinearities of the RF components in the receiver chain. Despite the intensity of the spurious signals, their impact can be reduced by narrowing the filtering stages and choosing the flux-ramp frequency carefully.
Fig. 4SSB phase noise for selected tones after channelization. The shaded green region represents the possible region for flux-ramp modulation (FRM) frequencies. The black dashed line represents the averaged noise level
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