Detector Log Video Amplifiers Overview Labtech has extensive experience in the design and manufacture of Detector Log Video Amplifiers (DLVAs). These devices are used extensively in applications requiring an output voltage related to the power of a received RF signal. These units are used extensively in direction finding and channelised receivers as well as phase array radar. In order to cope with a wide range of input signals a log amplifier is used to provide a linear voltage output per dBm of input power. Typically the input range of a DVLA will operate over 50dB or more with a base sensitivity less than -40dBm whilst providing linear conversion within ±1dB for all power levels, frequencies and temperatures. Where greater sensitivity and power levels are expected the Extended Range DLVA (ERDLVA) offers even greater performance. A feature of DLVAs is that the performance in intimately tied to the performance of the system in which they are to be integrated. Therefore, Labtech offers its extensive experience to design bespoke parts that meet specific requirement. The library of designs include: Multi-octave performance operating at frequencies up to 40GHz Dynamic ranges up to 80dB for ERDLVAs and 60dB for a DLVAs DC coupled and CW immune options Wide operating temperature range; -50°C to +100°C Small size and weight suitable for airborne applications Fast rise, settling and recovery times Labtech produces its DLVAs in class 10000 clean rooms and offers hermetic sealing and full environmental testing. Labtech Part Types The LMV005 is Labtech’s standard DLVA with a single detector diode offering a dynamic range of 45dB. Labtech’s extended range DLVA, LMV001 has two microwave detectors and a gain stage to achieve an impressive 80dB dynamic range. It also provides a buffered RF output to allow further processing of the RF signal. However, the majority of DLVA products are designed to meet specific requirements. Table 1 shows the specifications for some of the DLVAs in its product range. Page 1 of 7 Issue 1 12th June 2008 Table 1: DLVA Products Types Specifications Dynamic Range Frequency Min Frequency Max Logging range min Logging range max Frequency Flatness Log slope Log Linearity Slope accuracy TSS Temperature Stability Rise Time Settling time Recovery Time VSWR Absolute Max Input power DC Offset Gain Stage gain Number of detectors CW Immune LMV001 LMV005 LMV008 LMV009 LMV010 LMV011 LMV012 LMV014 Units 80 2 18 -70 10 ±2.0 50 ±1.00 ±2.5 -71 ±1.5 25 60 300 2:1 20 ±50.0 40 2 Yes 45 2 18 -40 5 ±1.0 50 ±2.5 -42 ±1.0 25 50 250 2:1 20 ±50.0 1 Yes 70 2 18 -55 15 ±2.0 50 ±2.0 -60 25 50 500 2:1 20 ±50.0 2 Yes 74 2 18 -61 7 ±1.75 70 ±1.25 -66 25 30 300 2:1 20 ±50.0 34-39 2 Yes 45 2 18 -40 5 ±1.5 50 ±0.75 ±1.00 -43 ±0.50 20 25 500 3:1 17 1 No 55 12 18 -40 15 ±1.5 50 ±0.50 ±1.00 -42 ±0.50 20 25 500 3:1 20 1 No 55 6 12 -40 15 ±1.5 50 ±0.50 ±1.00 -43 ±0.50 20 25 500 3:1 20 1 No 58 1.8 18.2 -42 17 ±1.5 50 ±0.75 -42 ±0.50 20 50 500 2.5:1 20 ±100.0 1 No dB GHz GHz dBm dBm dB mV/dB dB mV/dB dBm dB ns ns ns # dBm mV dB # - Note that since there are different ways of specifying DLVAs, not all parameters are applicable to all device types. Some key parameters to note are the dynamic range, log linearity, logging range, TSS (Tangential sensitivity) and frequency flatness. Typical DLVA Performance The logging range is the input power range over which the DLVA provides a voltage output proportional to the input power in dBm. For LMV11 for example, this is between a lower limit of -40dBm and an upper limit of +15dBm. The dynamic range is therefore 55dB. As an example, figure 1 shows a typical performance for LMV011. This plot shows the output voltage verses the input power over the full logging range for frequencies between 12 and 18GHz. The red frame represents the specification window. The plot shows the excellent linearity of output voltage over in excess of 300000:1 range of input powers, from 0.1uW to 31mW. It is useful to observe the performance in terms of the error over the logging range, expressed in dB as shown in figure 2. In this representation, the output power in dB is normalized to the ideal characteristic so that the error at each power level is easily seen. The unit is well in specification over the entire logging range. Tangential Signal Sensitivity (TSS) is a measurement related to the noise figure and the bandwidth and is the input power required to produce an 8dB signal to noise ratio. It is used as an indication of sensitivity performance because of the difficulty in measuring the noise of a logarithmic amplifier at the detected video output. For the LMV011, TSS is typically at a signal level around -44dBm and a measured SNR is plotted with the specification defined at -42dBm for 8dB SNR in figure 3. Page 2 of 7 Issue 1 12th June 2008 LMV011: Output Voltage vs Input Power 3500 Output Voltage (mV) 3000 2500 2000 1500 1000 500 0 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 Input Pow er (dBm ) Figure 1. Accuracy of Log Slope of 50mV/dB Figure 4 shows the frequency performance of LMV011 over the 12 to 18GHz frequency range, with input powers between -45 and +17dBm as a parameter. This shows a remarkably uniform frequency response for this circuit in which the RF feeds the detector directly and sees a wide range of impedance variation as the power level is changed. DLVAs are typically designed to detect RF power pulses, often in the presence of other RF signals, pulsed or CW. CW immunity may therefore be important for some applications and Labtech provide a novel circuit configuration to achieve this, and are exemplified in the LMV001, LMV005, LMV008 and LMV009 products. It is straightforward to add this CW immunity circuit to new designs. In order to respond to pulse signals, the DLVA must provide a rapid rise and settling time to track the incoming signal, so that the peak signal power can be unambiguously determined, and a fast recovery time so that it is ready to respond to the next input pulse it receives. Page 3 of 7 Issue 1 12th June 2008 LMV011: Log Error 3 Log Error (dB) 2 1 0 -1 -2 -3 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 Input Power (dBm) Figure 2. Normalised Log Error from -40 to +15dBm LMV011: SNR vs Input Power 20 18 16 SNR (dB) 14 12 10 8 6 4 2 0 -46 -45 -44 -43 -42 -41 -40 -39 -38 Input Power (dBm) Figure 3. Signal to Noise Ratio showing TSS better than -42dBm Page 4 of 7 Issue 1 12th June 2008 LMV011: Log Error vs Frequency 3 Log Error (dB) 2 1 0 -1 -2 -3 12 13 14 15 16 17 18 Frequency (GHz) Figure 4. Frequency performance for LMV011 for power levels -40 to +15dBm Figure 5 shows the rise time and settling time for LMV010. The rise time is defined as the time taken to get from 10% to 90% of the output value. For the LMV010 this is typically significantly less than 10ns. The settling time is defined as the time from 10% of the final signal to the time that the signal is within the specified excursion from the final output. For the LMV010 this is 1.0dB corresponding to ±50mV. The recovery time is the time taken for the output to fall to within a specified level of the initial input, and be ready to respond to a following pulse. A typical fall time for LMV010 is shown in figure 6. Page 5 of 7 Issue 1 12th June 2008 Figure 5. Rise time, overshoot and settling time for LMV010 Figure 6. Recovery time for LMV010 is less than 300ns. Page 6 of 7 Issue 1 12th June 2008 For Further information please contact: Labtech Microwave 8 Vincent Avenue Crownhill Milton Keynes MK8 0AB Alistair Frier Business Development Manager Tel: +44 (0) 1908 267656 (Direct) Tel: +44 (0) 1908 261755 (Switchboard) Fax: +44 (0) 1908 261788 Email:[email protected] WWW.labtechmicrowave.com Disclaimer:Whilst Labtech Microwave makes every effort to ensure that information contained in this document is accurate and correct although errors and omissions can occur. The information should be used as a guide only and Labtech Microwave does not accept any responsibility for any use made of this information. Page 7 of 7 Issue 1 12th June 2008