Chapter 6. Design of 40 GHz Frequency Synthesizer for IEEE Standard 802.15.3c
6.5. Measurement and Discussion
6.5.3. Closed-loop Measurement
varied. The divider chain only works with the control voltage between 0 and 1.1 V.
As for the synthesizer’s phase locking range, it can be seen that the charge pump only provides a control voltage from 0.3 V to 1 V. That is the reason why the synthesizer’s operation range shrinks. The design of the charge pump circuit, as shown in Figure 6.26, is rechecked. The current mirrors M20-23, M11-12 in the charge pump were designed with the minimum channel width. The purpose of this choice is to reduce the parasitic capacitance, leading to a high-speed operation. However, when the control voltage of the VCO is close to 0 or to the supply voltage 1.2 V, a large voltage mismatch would occur at the drain of transistor M21 and M22. As a result, severe current mismatch is caused and the net current of the charge pump cannot raise or decrease the control voltage of the VCO. If the long channel transistors are chosen, the current mismatch would be suppressed and the charge pump circuit would operate even when the control voltage of the VCO approaches 0 or 1.2 V.
Figure 6.37 Frequency range of VCO, divider chain and frequency synthesizer
By toggling the modules of programmable dividers, 4 different LO frequencies have been synthesized successfully for the 4 channels of the IEEE standard 802.15.3c. Figure 6.38 shows the screenshots of the 4 synthesized LO
38 39 40 41 42 43 44 45
Frequency Range (GHz)
Tuning range of VCO
Locking range of 32:1 divider chain Operation range of synthesizer
carriers, at 38.88 GHz, 40.32GHz, 41.76 GHz and 43.2 GHz. The reference spurs of the 4 LO carriers are all smaller than -50 dBc. However, it can be seen that the reference spur is not located exactly at 90 MHz offset, which equals the reference frequency. The observed spur has a frequency band around 90 MHz. This phenomenon might be caused by the FM broadcasting signal which is around 95 MHz.
For mm-wave measurement, the FM signal could easily be coupled to circuits through voltage supply or substrate, eventually appearing at the output.
(a) (b)
(c) (d)
Figure 6.38 4 LO carriers output at (a) 38.88 GHz, (b) 40.32 GHz, (c) 41.76 GHz and (d) 43.2 GHz
PH A S E NO IS E
S ettings Res idual Nois e S pot Nois e [T 1 ]
Signal Freq: 38.880049 GHz Evaluation from 1 kHz to 10 MHz 100 kHz -61.72 dBc /Hz
Signal Level: -8.67 dBm Residual P M 47.634 ° 1 MHz -88.64 dBc /Hz
Signal Freq ∆: -83.69 kHz Residual FM 145.287 kHz 3 MHz -99.72 dBc /Hz
Signal Level ∆: -2.42 dBm RMS Jitter 3.4032 ps 10 MHz -111.23 dBc/Hz
P H Noise RF A tten 0 dB T op -40 dBc/Hz
10 kHz 100 kHz 1 MHz
1 kHz 10 MHz
-110 -100 -90 -80 -70 -60 IFOVL -50
1 CLRWR SMTH 1%
2 CLRWR
A
SGL
Frequency Offset
(a)
PH A S E NO IS E
S ettings Res idual Nois e S pot Nois e [T 1 ]
Signal Freq: 43.200014 GHz Evaluation from 1 kHz to 10 MHz 100 kHz -58.88 dBc /Hz
Signal Level: -9.93 dBm Residual P M 72.926 ° 1 MHz -88.27 dBc /Hz
Signal Freq ∆: 4.59 kHz Residual FM 155.255 kHz 3 MHz -100.57 dBc/Hz
Signal Level ∆: -0.98 dBm RMS Jitter 4.6892 ps 10 MHz -111.34 dBc/Hz
P H Noise RF A tten 0 dB T op -30 dBc/Hz
10 kHz 100 kHz 1 MHz
1 kHz 10 MHz
-110 -100 -90 -80 -70 -60 -50 -40
1 CLRWR SMTH 1%
2 CLRWR
A
SGL
Frequency Offset
(b)
Figure 6.39 Phase noise measurement with Phase Noise Unit at (a) 38.88 GHz and (b) 43.2 GHz
The phase noise performance is measured using the phase noise unit of the spectrum analyzer. The phase noise unit is a software, which could extend the capability of the spectrum analyzer by phase noise tests [106]. Figure 6.39 shows two
screenshots of the phase noise measurement, at the highest LO carrier 43.2 GHz and the lowest LO carrier 38.88 GHz. As we can see, the designed 40 GHz frequency synthesizer resulted in good phase noise performance at 1 MHz offset. At these two LO frequencies, close to -90 dBc/Hz phase noise has been observed at 1 MHz offset.
The measurement results of the implemented 40 GHz frequency synthesizer are summarized in Table 6.13.
Table 6.13 Summary of measurement results VCO’s tuning range 38.2 – 44.2 GHz 32:1 divider chain’s locking
range 38.2 - 43.8 GHz
Synthesizer’s operation range 38.7 - 43.3 GHz
Output power (dBm) > -6 dBm
Phase noise @ 1MHz offset -89 dBc/Hz
Reference spur < -50 dBc
Power consumption 75 mW
In Table 6.14, the performance of the demonstrated 40 GHz frequency synthesizer is compared with the published works. As we can see, the designed frequency synthesizer achieves a wide frequency range from 38.7 GHz to 43.3 GHz.
It has an 11.2% frequency range, centered on 41 GHz. The output frequency range has successfully covered the desired 4 LO carriers for the 60 GHz high-data-rate WPAN application. As for the noise performance, the designed frequency synthesizer achieves -89 dBc/Hz phase noise at 1 MHz frequency offset, and reference spurs smaller than -50 dBc. These are comparable with the best results achieved so far. It is interesting to find that synthesizers with a large loop bandwidth all have poor phase noise performance. But the power consumption is a little high. The VCO’s buffer tree contributes most of the total power consumption. All in all, the performance of the 40 GHz frequency synthesizer compares well with most state-of-the-art versions.
Table 6.14 Performance comparisons of published mm-wave synthesizers
[107] [108] [101] [105] [109] [110] This
work Output
Freq.
(GHz)
39.1-41.6 (6.2%)
45.9-50.6 (9.8%)
35-41.8 (17.7%)
70-78 (10.8%)
58-60.4 (4.1%)
61-63 (3.2%)
38.7-43.3 (11.2%) Division
Ratio
512-2032 (Fra.)
1024 (PLL)
640-1240 (Integer)
1024-1984 (Integer)
256-258 (Integer)
1024 (PLL)
864-960 (Integer) LPF
Type
3rd-order off-chip
2nd-order on-chip
2nd-order off-chip
2nd-order on-chip
3rd-order on-chip
2nd-order on-chip
3rd-order off-chip Loop
BW 200 kHz 400 kHz 100 kHz 1 MHz N/A 1 MHz 100 kHz
Phase Noise (dBc/Hz)
-90 (1MHz)
-72 (1MHz)
-97 (1MHz)
-83 (1MHz)
-85 (1MHz)
-80 (1MHz)
-89 (1MHz) Spur
(dBc) -54 -40 -50 -49 -50 -49 -50
Ref.
Freq.
(MHz)
50 45.1 36 50 234.1 60 90
Supply Voltage (V)
1.2 1.5 1.2 1 1.2 1.2 1.2
DC power (mW)
64 57 80 65 80 78 75
Tech. 90 nm CMOS
130 nm CMOS
65 nm CMOS
65 nm CMOS
90 nm CMOS
90 nm CMOS
90 nm CMOS Area
(mm2)
1.54 (Inc. pad)
0.87 (Inc. pad)
1.1 (core)
0.16 (core)
0.95 (Inc. pad)
0.36 (core)
0.8 (Inc.pad)