Detector Log Video Amplifiers – An Overview

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.
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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.
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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.
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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
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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.
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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.
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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:a.frier@labtech.ltd.uk
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.
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Issue 1 12th June 2008